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crazylion lee

minoca/os: Minoca operating system - 1 views

github.com/os

os opensource

shared by crazylion lee on 15 Nov 16 - No Cached
  • crazylion lee on 15 Nov 16
     
    "Minoca operating system"
張 旭

Getting Started with Rails - Ruby on Rails Guides - 0 views

guides.rubyonrails.org/getting_started.html

shared by 張 旭 on 22 Jan 14 - Cached
  • A controller's purpose is to receive specific requests for the application.
  • Routing decides which controller receives which requests
  • The view should just display that information
  • ...55 more annotations...
  • view templates are written in a language called ERB (Embedded Ruby) which is converted by the request cycle in Rails before being sent to the user.
  • Each action's purpose is to collect information to provide it to a view.
  • A view's purpose is to display this information in a human readable format.
  • routing file which holds entries in a special DSL (domain-specific language) that tells Rails how to connect incoming requests to controllers and actions.
  • You can create, read, update and destroy items for a resource and these operations are referred to as CRUD operations
  • A controller is simply a class that is defined to inherit from ApplicationController.
  • If not found, then it will attempt to load a template called application/new. It looks for one here because the PostsController inherits from ApplicationController
  • :formats specifies the format of template to be served in response. The default format is :html, and so Rails is looking for an HTML template.
  • :handlers, is telling us what template handlers could be used to render our template.
  • When you call form_for, you pass it an identifying object for this form. In this case, it's the symbol :post. This tells the form_for helper what this form is for.
  • that the action attribute for the form is pointing at /posts/new
  • When a form is submitted, the fields of the form are sent to Rails as parameters.
  • parameters can then be referenced inside the controller actions, typically to perform a particular task
  • params method is the object which represents the parameters (or fields) coming in from the form.
  • Active Record is smart enough to automatically map column names to model attributes,
  • Rails uses rake commands to run migrations, and it's possible to undo a migration after it's been applied to your database
  • every Rails model can be initialized with its respective attributes, which are automatically mapped to the respective database columns.
  • migration creates a method named change which will be called when you run this migration.
  • The action defined in this method is also reversible, which means Rails knows how to reverse the change made by this migration, in case you want to reverse it later
  • Migration filenames include a timestamp to ensure that they're processed in the order that they were created.
  • @post.save returns a boolean indicating whether the model was saved or not.
  • prevents an attacker from setting the model's attributes by manipulating the hash passed to the model.
  • If you want to link to an action in the same controller, you don't need to specify the :controller option, as Rails will use the current controller by default.
  • inherits from ActiveRecord::Base
  • Active Record supplies a great deal of functionality to your Rails models for free, including basic database CRUD (Create, Read, Update, Destroy) operations, data validation, as well as sophisticated search support and the ability to relate multiple models to one another.
  • Rails includes methods to help you validate the data that you send to models
  • Rails can validate a variety of conditions in a model, including the presence or uniqueness of columns, their format, and the existence of associated objects.
  • redirect_to will tell the browser to issue another request.
  • rendering is done within the same request as the form submission
  • Each request for a comment has to keep track of the post to which the comment is attached, thus the initial call to the find method of the Post model to get the post in question.
  • pluralize is a rails helper that takes a number and a string as its arguments. If the number is greater than one, the string will be automatically pluralized.
  • The render method is used so that the @post object is passed back to the new template when it is rendered.
  • The method: :patch option tells Rails that we want this form to be submitted via the PATCH HTTP method which is the HTTP method you're expected to use to update resources according to the REST protocol.
  • it accepts a hash containing the attributes that you want to update.
  • field_with_errors. You can define a css rule to make them standout
  • belongs_to :post, which sets up an Active Record association
  • creates comments as a nested resource within posts
  • call destroy on Active Record objects when you want to delete them from the database.
  • Rails allows you to use the dependent option of an association to achieve this.
  • store all external data as UTF-8
  • you're better off ensuring that all external data is UTF-8
  • use UTF-8 as the internal storage of your database
  • Rails defaults to converting data from your database into UTF-8 at the boundary.
  • :patch
  • By default forms built with the form_for helper are sent via POST
  • The :method and :'data-confirm' options are used as HTML5 attributes so that when the link is clicked, Rails will first show a confirm dialog to the user, and then submit the link with method delete. This is done via the JavaScript file jquery_ujs which is automatically included into your application's layout (app/views/layouts/application.html.erb) when you generated the application.
  • Without this file, the confirmation dialog box wouldn't appear.
  • just defines the partial template we want to render
  • As the render method iterates over the @post.comments collection, it assigns each comment to
  • a local variable named the same as the partial
  • use the authentication system
  • require and permit
  • the method is often made private to make sure it can't be called outside its intended context.
  • standard CRUD actions in each controller in the following order: index, show, new, edit, create, update and destroy.
  • must be placed before any private or protected method in the controller in order to work
張 旭

Active Record Basics - Ruby on Rails Guides - 0 views

guides.rubyonrails.org/active_record_basics.html

ruby rails programming development framework model database object

shared by 張 旭 on 22 Jan 14 - No Cached
  • the model - which is the layer of the system responsible for representing business data and logic.
  • Active Record facilitates the creation and use of business objects whose data requires persistent storage to a database
  • Database Table - Plural with underscores separating words
  • ...33 more annotations...
  • objects carry both persistent data and behavior which operates on that data
  • Object-Relational Mapping, commonly referred to as its abbreviation ORM, is a technique that connects the rich objects of an application to tables in a relational database management system
  • Represent associations between these models
  • Validate models before they get persisted to the database
  • The idea is that if you configure your applications in the very same way most of the times then this should be the default way.
  • Rails will pluralize your class names to find the respective database table.
  • use the ActiveRecord::Base.table_name= method to specify the table name
  • Model Class - Singular with the first letter of each word capitalized
  • Foreign keys - These fields should be named following the pattern singularized_table_name_id
  • Primary keys - By default, Active Record will use an integer column named id as the table's primary key
  • created_at
  • updated_at
  • (table_name)_count - Used to cache the number of belonging objects on associations.
  • Object Relational Mapping
  • Single Table Inheritance (STI)
  • rake db:rollback
  • ActiveRecord::Base.primary_key=
  • CRUD is an acronym for the four verbs we use to operate on data: Create, Read, Update and Delete.
  • new method will return a new object
  • create will return the object and save it to the database.
  • Using the new method, an object can be instantiated without being saved
  • user.save will commit the record to the database
  • update_all class method
  • an Active Record object can be destroyed which removes it from the database
  • Validation is a very important issue to consider when persisting to database, so the methods create, save and update take it into account when running: they return false when validation fails and they didn't actually perform any operation on database.
  • a bang counterpart
  • Active Record callbacks allow you to attach code to certain events in the life-cycle of your models
  • Rails keeps track of which files have been committed to the database and provides rollback features
  • rake db:migrate
  • class_name.yml
  • Convention over Configuration
    • 張 旭
      張 旭 on 12 Apr 16
       
      Model 是單數，Table 是複數。想象一下，處理 Object 的時候是逐一處理，但是存放的地方是放了一堆 Objects。
    • 張 旭
      張 旭 on 12 Apr 16
       
      外鍵是單數的形式，這也很好理解：因為關聯到的是一個外部的 Object
張 旭

What is DevOps? | Atlassian - 0 views

www.atlassian.com/devops

devops system

shared by 張 旭 on 13 Nov 18 - No Cached
  • DevOps is a set of practices that automates the processes between software development and IT teams, in order that they can build, test, and release software faster and more reliably.
  • increased trust, faster software releases, ability to solve critical issues quickly, and better manage unplanned work.
  • bringing together the best of software development and IT operations.
  • ...39 more annotations...
  • DevOps is a culture, a movement, a philosophy.
  • a firm handshake between development and operations
  • DevOps isn’t magic, and transformations don’t happen overnight.
  • Infrastructure as code
  • Culture is the #1 success factor in DevOps.
  • Building a culture of shared responsibility, transparency and faster feedback is the foundation of every high performing DevOps team.
  •  'not our problem' mentality
  • DevOps is that change in mindset of looking at the development process holistically and breaking down the barrier between Dev and Ops.
  • Speed is everything.
  • Lack of automated test and review cycles block the release to production and poor incident response time kills velocity and team confidence
  • Open communication helps Dev and Ops teams swarm on issues, fix incidents, and unblock the release pipeline faster.
  • Unplanned work is a reality that every team faces–a reality that most often impacts team productivity.
  • “cross-functional collaboration.”
  • All the tooling and automation in the world are useless if they aren’t accompanied by a genuine desire on the part of development and IT/Ops professionals to work together.
  • DevOps doesn’t solve tooling problems. It solves human problems.
  • Forming project- or product-oriented teams to replace function-based teams is a step in the right direction.
  • sharing a common goal and having a plan to reach it together
  • join sprint planning sessions, daily stand-ups, and sprint demos.
  • DevOps culture across every department
  • open channels of communication, and talk regularly
  • DevOps isn’t one team’s job. It’s everyone’s job.
  • automation eliminates repetitive manual work, yields repeatable processes, and creates reliable systems.
  • Build, test, deploy, and provisioning automation
  • continuous delivery: the practice of running each code change through a gauntlet of automated tests, often facilitated by cloud-based infrastructure, then packaging up successful builds and promoting them up toward production using automated deploys.
  • automated deploys alert IT/Ops to server “drift” between environments, which reduces or eliminates surprises when it’s time to release.
  • “configuration as code.”
  • when DevOps uses automated deploys to send thoroughly tested code to identically provisioned environments, “Works on my machine!” becomes irrelevant.
  • A DevOps mindset sees opportunities for continuous improvement everywhere.
  • regular retrospectives
  • A/B testing
  • failure is inevitable. So you might as well set up your team to absorb it, recover, and learn from it (some call this “being anti-fragile”).
  • Postmortems focus on where processes fell down and how to strengthen them – not on which team member f'ed up the code.
  • Our engineers are responsible for QA, writing, and running their own tests to get the software out to customers.
  • How long did it take to go from development to deployment? 
  • How long does it take to recover after a system failure?
  • service level agreements (SLAs)
  • Devops isn't any single person's job. It's everyone's job.
  • DevOps is big on the idea that the same people who build an application should be involved in shipping and running it.
  • developers and operators pair with each other in each phase of the application’s lifecycle.
張 旭

Introduction - Packer by HashiCorp - 0 views

www.packer.io/index.html

vmware system packer devops virtualization

shared by 張 旭 on 03 Apr 19 - No Cached
  • A machine image is a single static unit that contains a pre-configured operating system and installed software which is used to quickly create new running machines.
  • 張 旭 on 03 Apr 19
     
    "A machine image is a single static unit that contains a pre-configured operating system and installed software which is used to quickly create new running machines."
張 旭

Helm | - 0 views

helm.sh/using_helm

kubernetes helm system

shared by 張 旭 on 17 Jul 19 - No Cached
  • Helm will figure out where to install Tiller by reading your Kubernetes configuration file (usually $HOME/.kube/config). This is the same file that kubectl uses.
  • kubectl cluster-info
  • Role-Based Access Control (RBAC) enabled
  • ...133 more annotations...
  • initialize the local CLI
  • install Tiller into your Kubernetes cluster
  • helm install
  • helm init --upgrade
  • By default, when Tiller is installed, it does not have authentication enabled.
  • helm repo update
  • Without a max history set the history is kept indefinitely, leaving a large number of records for helm and tiller to maintain.
  • helm init --upgrade
  • Whenever you install a chart, a new release is created.
  • one chart can be installed multiple times into the same cluster. And each can be independently managed and upgraded.
  • helm list function will show you a list of all deployed releases.
  • helm delete
  • helm status
  • you can audit a cluster’s history, and even undelete a release (with helm rollback).
  • the Helm server (Tiller).
  • The Helm client (helm)
  • brew install kubernetes-helm
  • Tiller, the server portion of Helm, typically runs inside of your Kubernetes cluster.
  • it can also be run locally, and configured to talk to a remote Kubernetes cluster.
  • Role-Based Access Control - RBAC for short
  • create a service account for Tiller with the right roles and permissions to access resources.
  • run Tiller in an RBAC-enabled Kubernetes cluster.
  • run kubectl get pods --namespace kube-system and see Tiller running.
  • helm inspect
  • Helm will look for Tiller in the kube-system namespace unless --tiller-namespace or TILLER_NAMESPACE is set.
  • For development, it is sometimes easier to work on Tiller locally, and configure it to connect to a remote Kubernetes cluster.
  • even when running locally, Tiller will store release configuration in ConfigMaps inside of Kubernetes.
  • helm version should show you both the client and server version.
  • Tiller stores its data in Kubernetes ConfigMaps, you can safely delete and re-install Tiller without worrying about losing any data.
  • helm reset
  • The --node-selectors flag allows us to specify the node labels required for scheduling the Tiller pod.
  • --override allows you to specify properties of Tiller’s deployment manifest.
  • helm init --override manipulates the specified properties of the final manifest (there is no “values” file).
  • The --output flag allows us skip the installation of Tiller’s deployment manifest and simply output the deployment manifest to stdout in either JSON or YAML format.
  • By default, tiller stores release information in ConfigMaps in the namespace where it is running.
  • switch from the default backend to the secrets backend, you’ll have to do the migration for this on your own.
  • a beta SQL storage backend that stores release information in an SQL database (only postgres has been tested so far).
  • Once you have the Helm Client and Tiller successfully installed, you can move on to using Helm to manage charts.
  • Helm requires that kubelet have access to a copy of the socat program to proxy connections to the Tiller API.
  • A Release is an instance of a chart running in a Kubernetes cluster. One chart can often be installed many times into the same cluster.
  • helm init --client-only
  • helm init --dry-run --debug
  • A panic in Tiller is almost always the result of a failure to negotiate with the Kubernetes API server
  • Tiller and Helm have to negotiate a common version to make sure that they can safely communicate without breaking API assumptions
  • helm delete --purge
  • Helm stores some files in $HELM_HOME, which is located by default in ~/.helm
  • A Chart is a Helm package. It contains all of the resource definitions necessary to run an application, tool, or service inside of a Kubernetes cluster.
  • it like the Kubernetes equivalent of a Homebrew formula, an Apt dpkg, or a Yum RPM file.
  • A Repository is the place where charts can be collected and shared.
  • Set the $HELM_HOME environment variable
  • each time it is installed, a new release is created.
  • Helm installs charts into Kubernetes, creating a new release for each installation. And to find new charts, you can search Helm chart repositories.
  • chart repository is named stable by default
  • helm search shows you all of the available charts
  • helm inspect
  • To install a new package, use the helm install command. At its simplest, it takes only one argument: The name of the chart.
  • If you want to use your own release name, simply use the --name flag on helm install
  • additional configuration steps you can or should take.
  • Helm does not wait until all of the resources are running before it exits. Many charts require Docker images that are over 600M in size, and may take a long time to install into the cluster.
  • helm status
  • helm inspect values
  • helm inspect values stable/mariadb
  • override any of these settings in a YAML formatted file, and then pass that file during installation.
  • helm install -f config.yaml stable/mariadb
  • --values (or -f): Specify a YAML file with overrides.
  • --set (and its variants --set-string and --set-file): Specify overrides on the command line.
  • Values that have been --set can be cleared by running helm upgrade with --reset-values specified.
  • Chart designers are encouraged to consider the --set usage when designing the format of a values.yaml file.
  • --set-file key=filepath is another variant of --set. It reads the file and use its content as a value.
  • inject a multi-line text into values without dealing with indentation in YAML.
  • An unpacked chart directory
  • When a new version of a chart is released, or when you want to change the configuration of your release, you can use the helm upgrade command.
  • Kubernetes charts can be large and complex, Helm tries to perform the least invasive upgrade.
  • It will only update things that have changed since the last release
  • $ helm upgrade -f panda.yaml happy-panda stable/mariadb
  • deployment
  • If both are used, --set values are merged into --values with higher precedence.
  • The helm get command is a useful tool for looking at a release in the cluster.
  • helm rollback
  • A release version is an incremental revision. Every time an install, upgrade, or rollback happens, the revision number is incremented by 1.
  • helm history
  • a release name cannot be re-used.
  • you can rollback a deleted resource, and have it re-activate.
  • helm repo list
  • helm repo add
  • helm repo update
  • The Chart Development Guide explains how to develop your own charts.
  • helm create
  • helm lint
  • helm package
  • Charts that are archived can be loaded into chart repositories.
  • chart repository server
  • Tiller can be installed into any namespace.
  • Limiting Tiller to only be able to install into specific namespaces and/or resource types is controlled by Kubernetes RBAC roles and rolebindings
  • Release names are unique PER TILLER INSTANCE
  • Charts should only contain resources that exist in a single namespace.
  • not recommended to have multiple Tillers configured to manage resources in the same namespace.
  • a client-side Helm plugin. A plugin is a tool that can be accessed through the helm CLI, but which is not part of the built-in Helm codebase.
  • Helm plugins are add-on tools that integrate seamlessly with Helm. They provide a way to extend the core feature set of Helm, but without requiring every new feature to be written in Go and added to the core tool.
  • Helm plugins live in $(helm home)/plugins
  • The Helm plugin model is partially modeled on Git’s plugin model
  • helm referred to as the porcelain layer, with plugins being the plumbing.
  • helm plugin install https://github.com/technosophos/helm-template
  • command is the command that this plugin will execute when it is called.
  • Environment variables are interpolated before the plugin is executed.
  • The command itself is not executed in a shell. So you can’t oneline a shell script.
  • Helm is able to fetch Charts using HTTP/S
  • Variables like KUBECONFIG are set for the plugin if they are set in the outer environment.
  • In Kubernetes, granting a role to an application-specific service account is a best practice to ensure that your application is operating in the scope that you have specified.
  • restrict Tiller’s capabilities to install resources to certain namespaces, or to grant a Helm client running access to a Tiller instance.
  • Service account with cluster-admin role
  • The cluster-admin role is created by default in a Kubernetes cluster
  • Deploy Tiller in a namespace, restricted to deploying resources only in that namespace
  • Deploy Tiller in a namespace, restricted to deploying resources in another namespace
  • When running a Helm client in a pod, in order for the Helm client to talk to a Tiller instance, it will need certain privileges to be granted.
  • SSL Between Helm and Tiller
  • The Tiller authentication model uses client-side SSL certificates.
  • creating an internal CA, and using both the cryptographic and identity functions of SSL.
  • Helm is a powerful and flexible package-management and operations tool for Kubernetes.
  • default installation applies no security configurations
  • with a cluster that is well-secured in a private network with no data-sharing or no other users or teams.
  • With great power comes great responsibility.
  • Choose the Best Practices you should apply to your helm installation
  • Role-based access control, or RBAC
  • Tiller’s gRPC endpoint and its usage by Helm
  • Kubernetes employ a role-based access control (or RBAC) system (as do modern operating systems) to help mitigate the damage that can be done if credentials are misused or bugs exist.
  • In the default installation the gRPC endpoint that Tiller offers is available inside the cluster (not external to the cluster) without authentication configuration applied.
  • Tiller stores its release information in ConfigMaps. We suggest changing the default to Secrets.
  • release information
  • charts
  • charts are a kind of package that not only installs containers you may or may not have validated yourself, but it may also install into more than one namespace.
  • As with all shared software, in a controlled or shared environment you must validate all software you install yourself before you install it.
  • Helm’s provenance tools to ensure the provenance and integrity of charts
  • 張 旭 on 17 Jul 19
     
    "Helm will figure out where to install Tiller by reading your Kubernetes configuration file (usually $HOME/.kube/config). This is the same file that kubectl uses."
張 旭

What exactly was the point of [ "x$var" = "xval" ]? - Vidar's Blog - 0 views

www.vidarholen.net/...blog

shell programming code

shared by 張 旭 on 21 Apr 21 - No Cached
  • x-hack
  • test "x$arg" = "x-f"
  • the utility used a simple recursive descent parser without backtracking, which gave unary operators precedence over binary operators and ignored trailing arguments.
  • ...3 more annotations...
  • The x-hack is effective because no unary operators can start with x.
  • the x-hack could be used to work around certain bugs all the way up until 2015, seven years after StackOverflow wrote it off as an archaic relic of the past!
  • The Dash issue of [ "(" = ")" ] was originally reported in a form that affected both Bash 3.2.48 and Dash 0.5.4 in 2008. You can still see this on macOS bash today
  • 張 旭 on 21 Apr 21
     
    "x$var"
張 旭

Kubernetes Deployments: The Ultimate Guide - Semaphore - 1 views

semaphoreci.com/...kubernetes-deployment

docker kubernetes devops system

shared by 張 旭 on 21 Oct 19 - No Cached
  • Continuous integration gives you confidence in your code. To extend that confidence to the release process, your deployment operations need to come with a safety belt.
  • these Kubernetes objects ensure that you can progressively deploy, roll back and scale your applications without downtime.
  • A pod is just a group of containers (it can be a group of one container) that run on the same machine, and share a few things together.
  • ...34 more annotations...
  • the containers within a pod can communicate with each other over localhost
  • From a network perspective, all the processes in these containers are local.
  • we can never create a standalone container: the closest we can do is create a pod, with a single container in it.
  • Kubernetes is a declarative system (by opposition to imperative systems).
  • All we can do, is describe what we want to have, and wait for Kubernetes to take action to reconcile what we have, with what we want to have.
  • In other words, we can say, “I would like a 40-feet long blue container with yellow doors“, and Kubernetes will find such a container for us. If it doesn’t exist, it will build it; if there is already one but it’s green with red doors, it will paint it for us; if there is already a container of the right size and color, Kubernetes will do nothing, since what we have already matches what we want.
  • The specification of a replica set looks very much like the specification of a pod, except that it carries a number, indicating how many replicas
  • What happens if we change that definition? Suddenly, there are zero pods matching the new specification.
  • the creation of new pods could happen in a more gradual manner.
  • the specification for a deployment looks very much like the one for a replica set: it features a pod specification, and a number of replicas.
  • Deployments, however, don’t create or delete pods directly.
  • When we update a deployment and adjust the number of replicas, it passes that update down to the replica set.
  • When we update the pod specification, the deployment creates a new replica set with the updated pod specification. That replica set has an initial size of zero. Then, the size of that replica set is progressively increased, while decreasing the size of the other replica set.
  • we are going to fade in (turn up the volume) on the new replica set, while we fade out (turn down the volume) on the old one.
  • During the whole process, requests are sent to pods of both the old and new replica sets, without any downtime for our users.
  • A readiness probe is a test that we add to a container specification.
  • Kubernetes supports three ways of implementing readiness probes:Running a command inside a container;Making an HTTP(S) request against a container; orOpening a TCP socket against a container.
  • When we roll out a new version, Kubernetes will wait for the new pod to mark itself as “ready” before moving on to the next one.
  • If there is no readiness probe, then the container is considered as ready, as long as it could be started.
  • MaxSurge indicates how many extra pods we are willing to run during a rolling update, while MaxUnavailable indicates how many pods we can lose during the rolling update.
  • Setting MaxUnavailable to 0 means, “do not shutdown any old pod before a new one is up and ready to serve traffic“.
  • Setting MaxSurge to 100% means, “immediately start all the new pods“, implying that we have enough spare capacity on our cluster, and that we want to go as fast as possible.
  • kubectl rollout undo deployment web
  • the replica set doesn’t look at the pods’ specifications, but only at their labels.
  • A replica set contains a selector, which is a logical expression that “selects” (just like a SELECT query in SQL) a number of pods.
  • it is absolutely possible to manually create pods with these labels, but running a different image (or with different settings), and fool our replica set.
  • Selectors are also used by services, which act as the load balancers for Kubernetes traffic, internal and external.
  • internal IP address (denoted by the name ClusterIP)
  • during a rollout, the deployment doesn’t reconfigure or inform the load balancer that pods are started and stopped. It happens automatically through the selector of the service associated to the load balancer.
  • a pod is added as a valid endpoint for a service only if all its containers pass their readiness check. In other words, a pod starts receiving traffic only once it’s actually ready for it.
  • In blue/green deployment, we want to instantly switch over all the traffic from the old version to the new, instead of doing it progressively
  • We can achieve blue/green deployment by creating multiple deployments (in the Kubernetes sense), and then switching from one to another by changing the selector of our service
  • kubectl label pods -l app=blue,version=v1.5 status=enabled
  • kubectl label pods -l app=blue,version=v1.4 status-
  • 張 旭 on 21 Oct 19
     
    "Continuous integration gives you confidence in your code. To extend that confidence to the release process, your deployment operations need to come with a safety belt."
張 旭

Connection and Privileges Needed - 0 views

www.percona.com/...privileges.html

mysql database backup percona xtradb

shared by 張 旭 on 02 Dec 19 - No Cached
  • Percona XtraBackup needs to be able to connect to the database server and perform operations on the server and the datadir when creating a backup, when preparing in some scenarios and when restoring it.
  • When xtrabackup is used, there are two actors involved: the user invoking the program - a system user - and the user performing action in the database server - a database user.
  • these are different users in different places, even though they may have the same username.
  • ...1 more annotation...
  • Once connected to the server, in order to perform a backup you will need READ and EXECUTE permissions at a filesystem level in the server’s datadir.
  • 張 旭 on 02 Dec 19
     
    "Percona XtraBackup needs to be able to connect to the database server and perform operations on the server and the datadir when creating a backup, when preparing in some scenarios and when restoring it. "
張 旭

The Backup Cycle - Full Backups - 0 views

www.percona.com/...full_backup.html

database mysql backup percona xtradb

shared by 張 旭 on 02 Dec 19 - No Cached
  • xtrabackup will not overwrite existing files, it will fail with operating system error 17, file exists.
  • Log copying thread checks the transactional log every second to see if there were any new log records written that need to be copied, but there is a chance that the log copying thread might not be able to keep up with the amount of writes that go to the transactional logs, and will hit an error when the log records are overwritten before they could be read.
  • It is safe to cancel at any time, because xtrabackup does not modify the database.
  • ...15 more annotations...
  • need to prepare it in order to restore it.
  • Data files are not point-in-time consistent until they are prepared, because they were copied at different times as the program ran, and they might have been changed while this was happening.
  • You can run the prepare operation on any machine; it does not need to be on the originating server or the server to which you intend to restore.
  • you simply run xtrabackup with the --prepare option and tell it which directory to prepare,
  • All following prepares will not change the already prepared data files
  • It is not recommended to interrupt xtrabackup process while preparing backup
  • Backup validity is not guaranteed if prepare process was interrupted.
  • If you intend the backup to be the basis for further incremental backups, you should use the --apply-log-only option when preparing the backup, or you will not be able to apply incremental backups to it.
  • Backup needs to be prepared before it can be restored.
  • xtrabackup --copy-back --target-dir=/data/backups/
  • The datadir must be empty before restoring the backup.
  • MySQL server needs to be shut down before restore is performed.
  • You cannot restore to a datadir of a running mysqld instance (except when importing a partial backup).
  • rsync -avrP /data/backup/ /var/lib/mysql/
  • chown -R mysql:mysql /var/lib/mysql
張 旭

Supported DDL operations for a CDC Replication Engine for Db2 Database - IBM Documentation - 1 views

www.ibm.com/...11.4.0

database sql

shared by 張 旭 on 03 Feb 23 - No Cached
  • SQL statements are divided into two categories: Data Definition Language (DDL) and Data Manipulation Language (DML).
  • DDL operations on a table may affect dependent objects such as constraints and Indexes.
  • 張 旭 on 03 Feb 23
     
    "DDL statements are used to describe a database, to define its structure, to create its objects and to create the table's sub-objects."
張 旭

architecture - Difference between a "coroutine" and a "thread"? - Stack Overflow - 0 views

stackoverflow.com/...tween-a-coroutine-and-a-thread

programming

shared by 張 旭 on 09 Jun 22 - No Cached
  • Co stands for cooperation. A co routine is asked to (or better expected to) willingly suspend its execution to give other co-routines a chance to execute too. So a co-routine is about sharing CPU resources (willingly) so others can use the same resource as oneself is using.
  • A thread on the other hand does not need to suspend its execution. Being suspended is completely transparent to the thread and the thread is forced by underlying hardware to suspend itself.
  • co-routines can not be concurrently executed and race conditions can not occur.
  • ...8 more annotations...
  • Concurrency is the separation of tasks to provide interleaved execution.
  • Parallelism is the simultaneous execution of multiple pieces of work in order to increase speed.
  • With threads, the operating system switches running threads preemptively according to its scheduler, which is an algorithm in the operating system kernel.
  • With coroutines, the programmer and programming language determine when to switch coroutines
  • In contrast to threads, which are pre-emptively scheduled by the operating system, coroutine switches are cooperative, meaning the programmer (and possibly the programming language and its runtime) controls when a switch will happen.
  • preemption
  • Coroutines are a form of sequential processing: only one is executing at any given time
  • Threads are (at least conceptually) a form of concurrent processing: multiple threads may be executing at any given time.
  • 張 旭 on 09 Jun 22
     
    "Co stands for cooperation. A co routine is asked to (or better expected to) willingly suspend its execution to give other co-routines a chance to execute too. So a co-routine is about sharing CPU resources (willingly) so others can use the same resource as oneself is using."
crazylion lee

BearSSL - 0 views

bearssl.org

openssl ssl tls

shared by crazylion lee on 11 Nov 16 - No Cached
  • crazylion lee on 11 Nov 16
     
    "BearSSL is an implementation of the SSL/TLS protocol (RFC 5246) written in C. It aims at offering the following features: Be correct and secure. In particular, insecure protocol versions and choices of algorithms are not supported, by design; cryptographic algorithm implementations are constant-time by default. Be small, both in RAM and code footprint. For instance, a minimal server implementation may fit in about 20 kilobytes of compiled code and 25 kilobytes of RAM. Be highly portable. BearSSL targets not only "big" operating systems like Linux and Windows, but also small embedded systems and even special contexts like bootstrap code. Be feature-rich and extensible. SSL/TLS has many defined cipher suites and extensions; BearSSL should implement most of them, and allow extra algorithm implementations to be added afterwards, possibly from third parties."
crazylion lee

Hammerspoon - 0 views

www.hammerspoon.org

automation lua osx mac

shared by crazylion lee on 24 Nov 16 - No Cached
  • crazylion lee on 24 Nov 16
     
    "This is a tool for powerful automation of OS X. At its core, Hammerspoon is just a bridge between the operating system and a Lua scripting engine. What gives Hammerspoon its power is a set of extensions that expose specific pieces of system functionality, to the user."
張 旭

Active Record Associations - Ruby on Rails Guides - 0 views

guides.rubyonrails.org/association_basics.html

rails database ruby relation

shared by 張 旭 on 12 Apr 16 - Cached
  • With Active Record associations, we can streamline these - and other - operations by declaratively telling Rails that there is a connection between the two models.
  • belongs_to has_one has_many has_many :through has_one :through has_and_belongs_to_many
  • an association is a connection between two Active Record models
  • ...195 more annotations...
  • Associations are implemented using macro-style calls, so that you can declaratively add features to your models
  • A belongs_to association sets up a one-to-one connection with another model, such that each instance of the declaring model "belongs to" one instance of the other model.
  • belongs_to associations must use the singular term.
  • belongs_to
  • A has_one association also sets up a one-to-one connection with another model, but with somewhat different semantics (and consequences).
  • This association indicates that each instance of a model contains or possesses one instance of another model
  • belongs_to
  • A has_many association indicates a one-to-many connection with another model.
  • This association indicates that each instance of the model has zero or more instances of another model.
  • belongs_to
  • A has_many :through association is often used to set up a many-to-many connection with another model
  • This association indicates that the declaring model can be matched with zero or more instances of another model by proceeding through a third model.
  • through:
  • through:
  • The collection of join models can be managed via the API
  • new join models are created for newly associated objects, and if some are gone their rows are deleted.
  • The has_many :through association is also useful for setting up "shortcuts" through nested has_many associations
  • A has_one :through association sets up a one-to-one connection with another model. This association indicates that the declaring model can be matched with one instance of another model by proceeding through a third model.
  • A has_and_belongs_to_many association creates a direct many-to-many connection with another model, with no intervening model.
  • id: false
  • The has_one relationship says that one of something is yours
  • using t.references :supplier instead.
  • declare a many-to-many relationship is to use has_many :through. This makes the association indirectly, through a join model
  • set up a has_many :through relationship if you need to work with the relationship model as an independent entity
  • set up a has_and_belongs_to_many relationship (though you'll need to remember to create the joining table in the database).
  • use has_many :through if you need validations, callbacks, or extra attributes on the join model
  • With polymorphic associations, a model can belong to more than one other model, on a single association.
  • belongs_to :imageable, polymorphic: true
  • a polymorphic belongs_to declaration as setting up an interface that any other model can use.
    • 張 旭
      張 旭 on 13 Apr 16
       
      _id 記錄的是不同類型的外連鍵 id；_type 記錄的是不同類型的表格名稱。
  • In designing a data model, you will sometimes find a model that should have a relation to itself
  • add a references column to the model itself
  • Controlling caching Avoiding name collisions Updating the schema Controlling association scope Bi-directional associations
  • All of the association methods are built around caching, which keeps the result of the most recent query available for further operations.
  • it is a bad idea to give an association a name that is already used for an instance method of ActiveRecord::Base. The association method would override the base method and break things.
  • You are responsible for maintaining your database schema to match your associations.
  • belongs_to associations you need to create foreign keys
  • has_and_belongs_to_many associations you need to create the appropriate join table
  • If you create an association some time after you build the underlying model, you need to remember to create an add_column migration to provide the necessary foreign key.
  • Active Record creates the name by using the lexical order of the class names
  • So a join between customer and order models will give the default join table name of "customers_orders" because "c" outranks "o" in lexical ordering.
  • For example, one would expect the tables "paper_boxes" and "papers" to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes", but it in fact generates a join table name of "paper_boxes_papers" (because the underscore '' is lexicographically _less than 's' in common encodings).
  • id: false
  • pass id: false to create_table because that table does not represent a model
  • By default, associations look for objects only within the current module's scope.
  • will work fine, because both the Supplier and the Account class are defined within the same scope.
  • To associate a model with a model in a different namespace, you must specify the complete class name in your association declaration:
  • class_name
  • class_name
  • Active Record provides the :inverse_of option
    • 張 旭
      張 旭 on 13 Apr 16
       
      意思是說第一次比較兩者的 first_name 是相同的；但透過 c 實體修改 first_name 之後，再次比較就不相同了，因為兩個是記憶體裡面兩個不同的物件。
  • preventing inconsistencies and making your application more efficient
  • Every association will attempt to automatically find the inverse association and set the :inverse_of option heuristically (based on the association name)
  • In database terms, this association says that this class contains the foreign key.
  • In all of these methods, association is replaced with the symbol passed as the first argument to belongs_to.
  • (force_reload = false)
  • The association method returns the associated object, if any. If no associated object is found, it returns nil.
  • the cached version will be returned.
  • The association= method assigns an associated object to this object.
  • Behind the scenes, this means extracting the primary key from the associate object and setting this object's foreign key to the same value.
  • The build_association method returns a new object of the associated type
  • but the associated object will not yet be saved.
  • The create_association method returns a new object of the associated type
  • once it passes all of the validations specified on the associated model, the associated object will be saved
  • raises ActiveRecord::RecordInvalid if the record is invalid.
  • dependent
  • counter_cache
  • :autosave :class_name :counter_cache :dependent :foreign_key :inverse_of :polymorphic :touch :validate
  • finding the number of belonging objects more efficient.
  • Although the :counter_cache option is specified on the model that includes the belongs_to declaration, the actual column must be added to the associated model.
  • add a column named orders_count to the Customer model.
  • :destroy, when the object is destroyed, destroy will be called on its associated objects.
  • deleted directly from the database without calling their destroy method.
  • Rails will not create foreign key columns for you
  • The :inverse_of option specifies the name of the has_many or has_one association that is the inverse of this association
  • set the :touch option to :true, then the updated_at or updated_on timestamp on the associated object will be set to the current time whenever this object is saved or destroyed
  • specify a particular timestamp attribute to update
  • If you set the :validate option to true, then associated objects will be validated whenever you save this object
  • By default, this is false: associated objects will not be validated when this object is saved.
  • where includes readonly select
  • make your code somewhat more efficient
  • no need to use includes for immediate associations
  • will be read-only when retrieved via the association
  • The select method lets you override the SQL SELECT clause that is used to retrieve data about the associated object
  • using the association.nil?
  • Assigning an object to a belongs_to association does not automatically save the object. It does not save the associated object either.
  • In database terms, this association says that the other class contains the foreign key.
  • the cached version will be returned.
  • :as :autosave :class_name :dependent :foreign_key :inverse_of :primary_key :source :source_type :through :validate
  • Setting the :as option indicates that this is a polymorphic association
  • :nullify causes the foreign key to be set to NULL. Callbacks are not executed.
  • It's necessary not to set or leave :nullify option for those associations that have NOT NULL database constraints.
  • The :source_type option specifies the source association type for a has_one :through association that proceeds through a polymorphic association.
  • The :source option specifies the source association name for a has_one :through association.
  • The :through option specifies a join model through which to perform the query
  • more efficient by including representatives in the association from suppliers to accounts
  • When you assign an object to a has_one association, that object is automatically saved (in order to update its foreign key).
  • If either of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.
  • If the parent object (the one declaring the has_one association) is unsaved (that is, new_record? returns true) then the child objects are not saved.
  • If you want to assign an object to a has_one association without saving the object, use the association.build method
  • collection(force_reload = false) collection<<(object, ...) collection.delete(object, ...) collection.destroy(object, ...) collection=(objects) collection_singular_ids collection_singular_ids=(ids) collection.clear collection.empty? collection.size collection.find(...) collection.where(...) collection.exists?(...) collection.build(attributes = {}, ...) collection.create(attributes = {}) collection.create!(attributes = {})
  • In all of these methods, collection is replaced with the symbol passed as the first argument to has_many, and collection_singular is replaced with the singularized version of that symbol.
  • The collection<< method adds one or more objects to the collection by setting their foreign keys to the primary key of the calling model
  • The collection.delete method removes one or more objects from the collection by setting their foreign keys to NULL.
  • objects will be destroyed if they're associated with dependent: :destroy, and deleted if they're associated with dependent: :delete_all
  • The collection.destroy method removes one or more objects from the collection by running destroy on each object.
  • The collection_singular_ids method returns an array of the ids of the objects in the collection.
  • The collection_singular_ids= method makes the collection contain only the objects identified by the supplied primary key values, by adding and deleting as appropriate
  • The default strategy for has_many :through associations is delete_all, and for has_many associations is to set the foreign keys to NULL.
  • The collection.clear method removes all objects from the collection according to the strategy specified by the dependent option
  • uses the same syntax and options as ActiveRecord::Base.find
  • The collection.where method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed.
  • The collection.build method returns one or more new objects of the associated type. These objects will be instantiated from the passed attributes, and the link through their foreign key will be created, but the associated objects will not yet be saved.
  • The collection.create method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through its foreign key will be created, and, once it passes all of the validations specified on the associated model, the associated object will be saved.
  • :as :autosave :class_name :dependent :foreign_key :inverse_of :primary_key :source :source_type :through :validate
  • :delete_all causes all the associated objects to be deleted directly from the database (so callbacks will not execute)
  • :nullify causes the foreign keys to be set to NULL. Callbacks are not executed.
  • where includes readonly select
  • :conditions :through :polymorphic :foreign_key
  • By convention, Rails assumes that the column used to hold the primary key of the association is id. You can override this and explicitly specify the primary key with the :primary_key option.
  • The :source option specifies the source association name for a has_many :through association.
  • You only need to use this option if the name of the source association cannot be automatically inferred from the association name.
  • The :source_type option specifies the source association type for a has_many :through association that proceeds through a polymorphic association.
  • The :through option specifies a join model through which to perform the query.
  • has_many :through associations provide a way to implement many-to-many relationships,
  • By default, this is true: associated objects will be validated when this object is saved.
  • where extending group includes limit offset order readonly select uniq
  • If you use a hash-style where option, then record creation via this association will be automatically scoped using the hash
  • The extending method specifies a named module to extend the association proxy.
  • Association extensions
  • The group method supplies an attribute name to group the result set by, using a GROUP BY clause in the finder SQL.
  • has_many :line_items, -> { group 'orders.id' },                        through: :orders
  • more efficient by including line items in the association from customers to orders
  • The limit method lets you restrict the total number of objects that will be fetched through an association.
  • The offset method lets you specify the starting offset for fetching objects via an association
  • The order method dictates the order in which associated objects will be received (in the syntax used by an SQL ORDER BY clause).
  • Use the distinct method to keep the collection free of duplicates.
  • mostly useful together with the :through option
  • -> { distinct }
  • .all.inspect
  • If you want to make sure that, upon insertion, all of the records in the persisted association are distinct (so that you can be sure that when you inspect the association that you will never find duplicate records), you should add a unique index on the table itself
  • unique: true
  • Do not attempt to use include? to enforce distinctness in an association.
  • multiple users could be attempting this at the same time
  • checking for uniqueness using something like include? is subject to race conditions
  • When you assign an object to a has_many association, that object is automatically saved (in order to update its foreign key).
  • If any of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.
  • If the parent object (the one declaring the has_many association) is unsaved (that is, new_record? returns true) then the child objects are not saved when they are added
  • All unsaved members of the association will automatically be saved when the parent is saved.
  • assign an object to a has_many association without saving the object, use the collection.build method
  • collection(force_reload = false) collection<<(object, ...) collection.delete(object, ...) collection.destroy(object, ...) collection=(objects) collection_singular_ids collection_singular_ids=(ids) collection.clear collection.empty? collection.size collection.find(...) collection.where(...) collection.exists?(...) collection.build(attributes = {}) collection.create(attributes = {}) collection.create!(attributes = {})
  • If the join table for a has_and_belongs_to_many association has additional columns beyond the two foreign keys, these columns will be added as attributes to records retrieved via that association.
  • Records returned with additional attributes will always be read-only
  • If you require this sort of complex behavior on the table that joins two models in a many-to-many relationship, you should use a has_many :through association instead of has_and_belongs_to_many.
  • aliased as collection.concat and collection.push.
  • The collection.delete method removes one or more objects from the collection by deleting records in the join table
  • not destroy the objects
  • The collection.destroy method removes one or more objects from the collection by running destroy on each record in the join table, including running callbacks.
  • not destroy the objects.
  • The collection.clear method removes every object from the collection by deleting the rows from the joining table.
  • not destroy the associated objects.
  • The collection.find method finds objects within the collection. It uses the same syntax and options as ActiveRecord::Base.find.
  • The collection.where method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed.
  • The collection.exists? method checks whether an object meeting the supplied conditions exists in the collection.
  • The collection.build method returns a new object of the associated type.
  • the associated object will not yet be saved.
  • the associated object will be saved.
  • The collection.create method returns a new object of the associated type.
  • it passes all of the validations specified on the associated model
  • :association_foreign_key :autosave :class_name :foreign_key :join_table :validate
  • The :foreign_key and :association_foreign_key options are useful when setting up a many-to-many self-join.
  • Rails assumes that the column in the join table used to hold the foreign key pointing to the other model is the name of that model with the suffix _id added.
  • If you set the :autosave option to true, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object.
  • By convention, Rails assumes that the column in the join table used to hold the foreign key pointing to this model is the name of this model with the suffix _id added.
  • By default, this is true: associated objects will be validated when this object is saved.
  • where extending group includes limit offset order readonly select uniq
  • set conditions via a hash
  • In this case, using @parts.assemblies.create or @parts.assemblies.build will create orders where the factory column has the value "Seattle"
  • If you use a hash-style where, then record creation via this association will be automatically scoped using the hash
  • using a GROUP BY clause in the finder SQL.
  • Use the uniq method to remove duplicates from the collection.
  • assign an object to a has_and_belongs_to_many association, that object is automatically saved (in order to update the join table).
  • If any of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.
  • If the parent object (the one declaring the has_and_belongs_to_many association) is unsaved (that is, new_record? returns true) then the child objects are not saved when they are added.
  • If you want to assign an object to a has_and_belongs_to_many association without saving the object, use the collection.build method.
  • Normal callbacks hook into the life cycle of Active Record objects, allowing you to work with those objects at various points
  • define association callbacks by adding options to the association declaration
  • Rails passes the object being added or removed to the callback.
  • stack callbacks on a single event by passing them as an array
  • If a before_add callback throws an exception, the object does not get added to the collection.
  • if a before_remove callback throws an exception, the object does not get removed from the collection
  • extend these objects through anonymous modules, adding new finders, creators, or other methods.
  • order_number
  • use a named extension module
  • proxy_association.owner returns the object that the association is a part of.
crazylion lee

Homepage | Celery: Distributed Task Queue - 0 views

www.celeryproject.org

python queue job background message

shared by crazylion lee on 04 Dec 16 - Cached
  • crazylion lee on 04 Dec 16
     
    "Celery is an asynchronous task queue/job queue based on distributed message passing. It is focused on real-time operation, but supports scheduling as well. The execution units, called tasks, are executed concurrently on a single or more worker servers using multiprocessing, Eventlet, or gevent. Tasks can execute asynchronously (in the background) or synchronously (wait until ready)."
crazylion lee

YubiKey 4 and YubiKey 4 Nano | U2F, OTP, PIV | Yubico - 0 views

www.yubico.com/...yubikey4

key lock hardware

shared by crazylion lee on 26 Apr 16 - No Cached
  • crazylion lee on 26 Apr 16
     
    "The YubiKey 4 is the strong authentication bullseye the industry has been aiming at for years, enabling one single key to secure an unlimited number of applications. Yubico's 4th generation YubiKey is built on high-performance secure elements. It includes the same range of one-time password and public key authentication protocols as in the YubiKey NEO, excluding NFC, but with stronger public/private keys, faster crypto operations and the world's first touch-to-sign feature. With the YubiKey 4 platform, we have further improved our manufacturing and ordering process, enabling customers to order exactly what functions they want in 500+ unit volumes, with no secrets stored at Yubico or shared with a third-party organization. The best part? An organization can securely customize 1,000 YubiKeys in less than 10 minutes. For customers who require NFC, the YubiKey NEO is our full-featured key with both contact (USB) and contactless (NFC, MIFARE) communications."
crazylion lee

Supervisor: A Process Control System - supervisor 3.1a1-dev documentation - 1 views

supervisord.org

monitoring sysadmin python linux unix supervisor

shared by crazylion lee on 13 Feb 14 - Cached
  • crazylion lee on 13 Feb 14
     
    Supervisor is a client/server system that allows its users to monitor and control a number of processes on UNIX-like operating systems. It shares some of the same goals of programs like launchd, daemontools, and runit. Unlike some of these programs, it is not meant to be run as a substitute for init as "process id 1". Instead it is meant to be used to control processes related to a project or a customer, and is meant to start like any other program at boot time.
crazylion lee

Tails - Privacy for anyone anywhere - 1 views

tails.boum.org/index.en.html

privacy linux security distribution

shared by crazylion lee on 21 Nov 15 - No Cached
  • crazylion lee on 21 Nov 15
     
    "Tails is a live operating system, that you can start on almost any computer from a DVD, USB stick, or SD card. It aims at preserving your privacy and anonymity, and helps you to: "
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