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張 旭

Rails Routing from the Outside In - Ruby on Rails Guides - 0 views

guides.rubyonrails.org/routing.html

rails router path url namespace

shared by 張 旭 on 09 Mar 14 - Cached
  • Resource routing allows you to quickly declare all of the common routes for a given resourceful controller.
  • Rails would dispatch that request to the destroy method on the photos controller with { id: '17' } in params.
  • a resourceful route provides a mapping between HTTP verbs and URLs to controller actions.
  • ...86 more annotations...
  • each action also maps to particular CRUD operations in a database
  • resource :photo and resources :photos creates both singular and plural routes that map to the same controller (PhotosController).
  • One way to avoid deep nesting (as recommended above) is to generate the collection actions scoped under the parent, so as to get a sense of the hierarchy, but to not nest the member actions.
  • to only build routes with the minimal amount of information to uniquely identify the resource
  • The shallow method of the DSL creates a scope inside of which every nesting is shallow
  • These concerns can be used in resources to avoid code duplication and share behavior across routes
  • add a member route, just add a member block into the resource block
  • You can leave out the :on option, this will create the same member route except that the resource id value will be available in params[:photo_id] instead of params[:id].
  • Singular Resources
  • use a singular resource to map /profile (rather than /profile/:id) to the show action
  • Passing a String to get will expect a controller#action format
  • workaround
  • organize groups of controllers under a namespace
  • route /articles (without the prefix /admin) to Admin::ArticlesController
  • route /admin/articles to ArticlesController (without the Admin:: module prefix)
  • Nested routes allow you to capture this relationship in your routing.
  • helpers take an instance of Magazine as the first parameter (magazine_ads_url(@magazine)).
  • Resources should never be nested more than 1 level deep.
  • via the :shallow option
  • a balance between descriptive routes and deep nesting
  • :shallow_path prefixes member paths with the specified parameter
  • Routing Concerns allows you to declare common routes that can be reused inside other resources and routes
  • Rails can also create paths and URLs from an array of parameters.
  • use url_for with a set of objects
  • In helpers like link_to, you can specify just the object in place of the full url_for call
  • insert the action name as the first element of the array
  • This will recognize /photos/1/preview with GET, and route to the preview action of PhotosController, with the resource id value passed in params[:id]. It will also create the preview_photo_url and preview_photo_path helpers.
  • pass :on to a route, eliminating the block:
  • Collection Routes
  • This will enable Rails to recognize paths such as /photos/search with GET, and route to the search action of PhotosController. It will also create the search_photos_url and search_photos_path route helpers.
  • simple routing makes it very easy to map legacy URLs to new Rails actions
  • add an alternate new action using the :on shortcut
  • When you set up a regular route, you supply a series of symbols that Rails maps to parts of an incoming HTTP request.
  • :controller maps to the name of a controller in your application
  • :action maps to the name of an action within that controller
  • optional parameters, denoted by parentheses
  • This route will also route the incoming request of /photos to PhotosController#index, since :action and :id are
  • use a constraint on :controller that matches the namespace you require
  • dynamic segments don't accept dots
  • The params will also include any parameters from the query string
  • :defaults option.
  • set params[:format] to "jpg"
  • cannot override defaults via query parameters
  • specify a name for any route using the :as option
  • create logout_path and logout_url as named helpers in your application.
  • Inside the show action of UsersController, params[:username] will contain the username for the user.
  • should use the get, post, put, patch and delete methods to constrain a route to a particular verb.
  • use the match method with the :via option to match multiple verbs at once
  • Routing both GET and POST requests to a single action has security implications
  • 'GET' in Rails won't check for CSRF token. You should never write to the database from 'GET' requests
  • use the :constraints option to enforce a format for a dynamic segment
  • constraints
  • don't need to use anchors
  • Request-Based Constraints
  • the same name as the hash key and then compare the return value with the hash value.
  • constraint values should match the corresponding Request object method return type
    • 張 旭
      張 旭 on 11 Apr 16
       
      應該就是檢查來源的 request， 如果是某個特定的 request 來訪問的，就通過。
  • blacklist
    • 張 旭
      張 旭 on 11 Apr 16
       
      這裡有點複雜 ...
  • redirect helper
  • reuse dynamic segments from the match in the path to redirect
  • this redirection is a 301 "Moved Permanently" redirect.
  • root method
  • put the root route at the top of the file
  • The root route only routes GET requests to the action.
  • root inside namespaces and scopes
  • For namespaced controllers you can use the directory notation
  • Only the directory notation is supported
  • use the :constraints option to specify a required format on the implicit id
  • specify a single constraint to apply to a number of routes by using the block
  • non-resourceful routes
  • :id parameter doesn't accept dots
  • :as option lets you override the normal naming for the named route helpers
  • use the :as option to prefix the named route helpers that Rails generates for a rout
  • prevent name collisions
  • prefix routes with a named parameter
  • This will provide you with URLs such as /bob/articles/1 and will allow you to reference the username part of the path as params[:username] in controllers, helpers and views
  • :only option
  • :except option
  • generate only the routes that you actually need can cut down on memory use and speed up the routing process.
  • alter path names
  • http://localhost:3000/rails/info/routes
  • rake routes
  • setting the CONTROLLER environment variable
  • Routes should be included in your testing strategy
  • assert_generates assert_recognizes assert_routing
張 旭

mqtt - 0 views

mosquitto.org/mqtt-7.html

mqtt server queue message system

shared by 張 旭 on 15 Feb 17 - No Cached
  • MQTT is a lightweight publish/subscribe messaging protocol. It is useful for use with low power sensors
  • The MQTT protocol is based on the principle of publishing messages and subscribing to topics, or "pub/sub".
  • Multiple clients connect to a broker and subscribe to topics that they are interested in
  • ...22 more annotations...
  • Many clients may subscribe to the same topics
  • The broker and MQTT act as a simple, common interface for everything to connect to
  • Messages in MQTT are published on topics
  • no need to configure a topic, publishing on it is enough
  • Topics are treated as a hierarchy, using a slash (/) as a separator.
  • Clients can receive messages by creating subscriptions
  • A subscription may be to an explicit topic
  • Two wildcards are available, + or #.
  • # can be used as a wildcard for all remaining levels of hierarchy
  • + can be used as a wildcard for a single level of hierarchy
  • Zero length topic levels are valid, which can lead to some slightly non-obvious behaviour.
  • The QoS defines how hard the broker/client will try to ensure that a message is received.
  • Messages may be sent at any QoS level, and clients may attempt to subscribe to topics at any QoS level
  • the client chooses the maximum QoS it will receive
  • if a client is subscribed with QoS 2 and a message is published on QoS 0, the client will receive it on QoS 0.
  • 1: The broker/client will deliver the message at least once, with confirmation required.
  • All messages may be set to be retained.
  • the broker will keep the message even after sending it to all current subscribers
  • useful as a "last known good" mechanism
  • If clean session is set to false, then the connection is treated as durable
  • when the client disconnects, any subscriptions it has will remain and any subsequent QoS 1 or 2 messages will be stored until it connects again in the future
  • If clean session is true, then all subscriptions will be removed for the client when it disconnects
張 旭

Containers Vs. Config Management - 0 views

blog.containership.io/config-management-e64cbb744a94

docker devops deploy config ansible puppet system

shared by 張 旭 on 16 Feb 17 - No Cached
  • With configuration management systems, you write code that describes how you want some component of your systems to be installed and configured, and when you execute the code on your server, it should end up in the desired state.
  • building a hosting platform that is capable of a lot of things that system administrators used to do manually
  • build modules on deployment via bundler or npm or similar, it can be incredibly slow to run, taking minutes or longer in some cases
  • ...10 more annotations...
  • pulling from git is slow.
  • deploying with configuration management tools is a pain in the ass and error prone.
  • Support for containers has existed in the Linux kernel since version 2.6.24 when cgroup support was added
  • All of the logic that used to live in your cookbooks/playbooks/manifests/etc now lives in a Dockerfile that resides directly in the repository for the application it is designed to build
  • All of the dependencies of the application are bundled with the container which means no need to build on the fly on every server during deployment.
  • Containers bring standardization which allows for systems like centralized logging, monitoring, and metrics to easily snap into place no matter what is running in the container.
  • Dockerfiles do not give you the same level of control over configuration as your application transitions between environments, like dev, staging, and production.
  • You may even need to have different Dockerfile’s for each environment in certain cases.
  • configuration management systems now have hooks for docker integration.
  • Config management will only be used to install Docker, an orchestration system, configure PAM/SSH auth, and tune OS sysctl values.
  • 張 旭 on 16 Feb 17
     
    "With configuration management systems, you write code that describes how you want some component of your systems to be installed and configured, and when you execute the code on your server, it should end up in the desired state."
張 旭

Probably Done Before: Visualizing Docker Containers and Images - 0 views

merrigrove.blogspot.tw/...ker-containers-and-images.html

docker technology system

shared by 張 旭 on 07 Apr 17 - No Cached
  •  In my opinion, understanding how a technology works under the hood is the best way to achieve learning speed and to build confidence that you are using the tool in the correct way.
  • union view
    • 張 旭
      張 旭 on 07 Apr 17
       
      把多層 image layer 串接起來，看上去就像是在讀一個 image 檔案而已。
  • The top-level layer may be read by a union-ing file system (AUFS on my docker implementation) to present a single cohesive view of all the changes as one read-only file system
  • ...36 more annotations...
  • it is nearly the same thing as an image, except that the top layer is read-write
  • A container is defined only as a read-write layer atop an image (of read-only layers itself).  It does not have to be running.
  • a running container
    • 張 旭
      張 旭 on 07 Apr 17
       
      之前一直搞錯了！不是 run 起來的才會叫 container，只要有 read-write layer 就是了！
  • the the isolated process-space and processes within
  • A running container is defined as a read-write "union view" and
  • kernel-level technologies like cgroups, namespaces
  • The processes within this process-space may change, delete or create files within the "union view" file that will be captured in the read-write layer
  • there is no longer a running container
    • 張 旭
      張 旭 on 07 Apr 17
       
      這行指令執行結束之後，running container 就停掉了，但是該 container 還在！
  • each layer contains a pointer to a parent layer using the Id
  • The 'docker create' command adds a read-write layer to the top stack based on the image id.  It does not run this container.
  • The command 'docker start' creates a process space around the union view of the container's layers.
  • can only be one process space per container.
  • the docker run command starts with an image, creates a container, and starts the container
  • 'git pull' (which is a combination of 'git fetch' and 'git merge')
  • 'docker ps' lists out the inventory of running containers on your system
  • 'docker ps -a' where the 'a' is short for 'all' lists out all the containers on your system, whether stopped or running.
  • Only those images that have containers attached to them or that have been pulled are considered top-level.
  • 'docker stop' issues a SIGTERM to a running container which politely stops all the processes in that process-space.
  • results is a normal, but non-running, container
  • 'docker kill' issues a non-polite SIGKILL command to all the processes in a running container.
  • 'docker stop' and 'docker kill' which send actual UNIX signals to a running process
  • 'docker pause' uses a special cgroups feature to freeze/pause a running process-space
  • 'docker rm' removes the read-write layer that defines a container from your host system
  • It effectively deletes files
  • 'docker rmi' removes the read-layer that defines a "union view" of an image.
  • 'docker commit' takes a container's top-level read-write layer and burns it into a read-only layer.
  • turns a container (whether running or stopped) into an immutable image
  • uses the FROM directive in the Dockerfile file as the starting image and iteratively 1) runs (create and start) 2) modifies and 3) commits.
  • At each step in the iteration a new layer is created.
  • 'docker exec' command runs on a running container and executes a process in that running container's process space
  • 'docker inspect' fetches the metadata that has been associated with the top-layer of the container or image
  • 'docker save' creates a single tar file that can be used to import on a different host system
  • only be run on an image
  • 'docker export' command creates a tar file of the contents of the "union view" and flattens it for consumption for non-Docker usages
  • This command removes the metadata and the layers.  This command can only be run on containers.
  • 'docker history' command takes an image-id and recursively prints out the read-only layers
張 旭

How to write excellent Dockerfiles - 0 views

rock-it.pl/to-write-excellent-dockerfiles

docker server system

shared by 張 旭 on 10 Apr 17 - No Cached
  • minimize image size, build time and number of layers.
  • maximize build cache usage
  • Container should do one thing
    • 張 旭
      張 旭 on 10 Apr 17
       
      這個有待商榷，在 baseimage 的 blog 介紹中有詳細的討論。
  • ...25 more annotations...
  • Use COPY and RUN commands in proper order
  • Merge multiple RUN commands into one
  • alpine versions should be enough
  • Use exec inside entrypoint script
  • Prefer COPY over ADD
  • Specify default environment variables, ports and volumes inside Dockerfile
  • problems with zombie processes
  • prepare separate Docker image for each component, and use Docker Compose to easily start multiple containers at the same time
  • Layers are cached and reused
  • Layers are immutable
  • They both makes you cry
  • rely on our base image updates
  • make a cleanup
  • alpine is a very tiny linux distribution, just about 4 MB in size.
  • Your disk will love you :)
  • WORKDIR command changes default directory, where we run our RUN / CMD / ENTRYPOINT commands.
  • CMD is a default command run after creating container without other command specified.
  • put your command inside array
  • entrypoint adds complexity
  • Entrypoint is a script, that will be run instead of command, and receive command as arguments
  • Without it, we would not be able to stop our application grecefully (SIGTERM is swallowed by bash script).
  • Use "exec" inside entrypoint script
  • ADD has some logic for downloading remote files and extracting archives.
  • stick with COPY.
  • ADD
    • 張 旭
      張 旭 on 10 Apr 17
       
      不是說要用 COPY 嗎？
張 旭

javascript - How do I "think in AngularJS" if I have a jQuery background? - Stack Overflow - 0 views

stackoverflow.com/...-if-i-have-a-jquery-background

jquery javascript angular programming architecture development google angularjs web

shared by 張 旭 on 02 Oct 13 - No Cached
  • in AngularJS, we have a separate model layer that we can manage in any way we want, completely independently from the view.
  • keep your concerns separate
  • do DOM manipulation and augment your view with directives
  • ...34 more annotations...
  • DI means that you can declare components very freely and then from any other component, just ask for an instance of it and it will be granted
  • do test-driven development iteratively in AngularJS!
  • only do DOM manipulation in a directive
  • with ngClass we can dynamically update the class;
  • ngBind allows two-way data binding;
  • ngShow and ngHide programmatically show or hide an element;
  • The less DOM manipulation, the easier directives are to test, the easier they are to style, the easier they are to change in the future, and the more re-usable and distributable they are.
  • still wrong.
  • Before doing DOM manipulation anywhere in your application, ask yourself if you really need to.
  • a few things wrong with this
  • jQuery was never necessary
  • use angular.element and our component will still work when dropped into a project that doesn't have jQuery.
  • just use angular.element
  • the element that is passed to the link function would already be a jQuery element!
  • directives aren't just collections of jQuery-like functions
  • Directives are actually extensions of HTML
  • If HTML doesn't do something you need it to do, you write a directive to do it for you, and then use it just as if it was part of HTML.
  • think how the team would accomplish it to fit right in with ngClick, ngClass, et al.
  • Don't even use jQuery. Don't even include it.
  • ry to think about how to do it within the confines the AngularJS.
  • In jQuery, selectors are used to find DOM elements and then bind/register event handlers to them.
  • Views are (declarative) HTML that contain AngularJS directives
  • Directives set up the event handlers behind the scenes for us and give us dynamic databinding.
  • Views are tied to models (via scopes). Views are a projection of the model
  • In AngularJS, think about models, rather than jQuery-selected DOM elements that hold your data.
  • AngularJS uses controllers and directives (each of which can have their own controller, and/or compile and linking functions) to remove behavior from the view/structure (HTML). Angular also has services and filters to help separate/organize your application.
  • Think about your models
  • Think about how you want to present your models -- your views.
  • using the necessary directives to get dynamic databinding.
  • Attach a controller to each view (using ng-view and routing, or ng-controller)
  • Make controllers as thin as possible.
  • You can do a lot with jQuery without knowing about how JavaScript prototypal inheritance works.
  • jQuery is a library
  • AngularJS is a beautiful client-side framework
張 旭

The Flatiron School | Why You Don't Need Has_and_belongs_to_many... - 0 views

blog.flatironschool.com/...t-need-has-and-belongs-to-many

rails model database

shared by 張 旭 on 14 Dec 14 - No Cached
  • When creating associations between models, you almost never know how this relationship will blossom as your application grows.
  • setup a solid has_many :through relationship with an associated join table, you provide yourself with a huge amount of flexibility down the road.
  • A has_many :through association is used to setup a many to many relationship with another model
  • ...2 more annotations...
  • This relationship now allows for extending the association within the join table.
  • You should use has_many :through if you need validations, callbacks, or extra attributes on the join model
張 旭

Embracing REST with mind, body and soul « Plataformatec Blog - 0 views

blog.plataformatec.com.br/...g-rest-with-mind-body-and-soul

rails REST MVC controller

shared by 張 旭 on 30 Dec 14 - No Cached
  • gain with respond_with introduction is more obvious if you compare index, new and show actions
    • 張 旭
      張 旭 on 30 Dec 14
       
      看起來 respond_with 會根據 request 型態自動回覆對應型態的 response
  • you can define supported formats at the class level and tell in the instance the resource to be represented by those formats.
  • when a request comes, for example with format xml, it will first search for a template at users/index.xml. If the template is not available, it tries to render the resource given (in this case, @users) by calling :to_xml on it
  • ...6 more annotations...
  • how to render our resources depending on the format AND HTTP verb
  • By default, ActionController::Responder holds all formats behavior in a method called to_format.
  • Suddenly we realized that respond_with is useful just for GET requests
  • it renders the resource based on the HTTP verb and whether it has errors or not
  • Your controller code just have to send the resource using respond_with(@resource) and respond_with will call ActionController::Responder which will know what to do.
    • 張 旭
      張 旭 on 30 Dec 14
       
      簡單說，就是只要寫 respond_with 就好了，其它都不用管了。Responder 會幫你判斷 HTTP 的動作。
  • Anything that responds to :call can be a responder, so you can create your custom classes or even give procs, fibers and so on.
crazylion lee

Keepalived for Linux - 0 views

www.keepalived.org

clustering HA failover keepalived

shared by crazylion lee on 15 Aug 14 - Cached
  • crazylion lee on 15 Aug 14
     
    Keepalived is a routing software written in C. The main goal of this project is to provide simple and robust facilities for loadbalancing and high-availability to Linux system and Linux based infrastructures. Loadbalancing framework relies on well-known and widely used Linux Virtual Server (IPVS) kernel module providing Layer4 loadbalancing. Keepalived implements a set of checkers to dynamically and adaptively maintain and manage loadbalanced server pool according their health. On the other hand high-availability is achieved by VRRP protocol. VRRP is a fundamental brick for router failover. In addition, Keepalived implements a set of hooks to the VRRP finite state machine providing low-level and high-speed protocol interactions. Keepalived frameworks can be used independently or all together to provide resilient infrastructures.
張 旭

单表60亿记录等大数据场景的MySQL优化和运维之道 - 快课网 - 0 views

www.cricode.com/3981.html

mysql system performance HA database

shared by 張 旭 on 18 Nov 15 - No Cached
  • 存储引擎使用InnoDB
  • 变长字符串尽量使用varchar varbinary
  • 不在数据库中存储图片、文件等
  • ...34 more annotations...
  • 库名、表名、字段名、索引名使用小写字母，以下划线分割 ，需要见名知意
  • 所有字段均定义为NOT NULL ，除非你真的想存Null
  • 使用TIMESTAMP存储时间
  • 使用DECIMAL存储精确浮点数，用float有的时候会有问题
  • 单个索引字段数不超过5，单表索引数量不超过5，索引设计遵循B+ Tree索引最左前缀匹配原则
  • 建立的索引能覆盖80%主要的查询，不求全，解决问题的主要矛盾
  • 避免冗余索引
  • 索引这个东西是一把双刃剑，在加速读的同时也引入了很多额外的写入和锁，降低写入能力
  • 字段定义为varchar，但传入的值是个int，就会导致全表扫描，要求程序端要做好类型检查
  • 避免使用大表的JOIN，MySQL优化器对join优化策略过于简单
  • UPDATE、DELETE语句不使用LIMIT ，容易造成主从不一致
  • 高危操作检查，Drop前做好数据备份
  • 日志分析，主要是指的MySQL慢日志和错误日志
  • Percona公司根据Facebook OSC思路，用perl重写了一版，就是我们现在用得很多的pt-online-schema-change，软件本身非常成熟，支持目前主流版本
  • 原生主从同步肯定存在着性能和安全性问题
  • Sharding is very complex, so itʼs best not to shard until itʼs obvious that you will actually need to!
  • 有中间层控制拆分逻辑最好，否则拆分过细管理成本会很高
  • 全量binlog备份
  • xtrabackup热备
  • 采用分布式文件系统存储备份
  • 基于库级别的复制，所以如果你只有一个库，使用这个意义不大
  • 半同步复制，从5.5开始支持
  • 半同步通过从库返回ACK这种方式确认从库收到数据
  • Secondsbehindmaster来判断延时不可靠，在网络抖动或者一些特殊参数配置情况下，会造成这个值是0但其实延时很大了。通过heartbeat表插入时间戳这种机制判断延时是更靠谱的
  • Binlog格式，建议都采用row格式，数据一致性更好
  • 成熟开源事务存储引擎，支持ACID，支持事务四个隔离级别，更好的数据安全性，高性能高并发，MVCC，细粒度锁，支持O_DIRECT
  • 数据安全性至关重要，InnoDB完胜
  • 主流使用TokuDB主要是看中了它的高压缩比
  • TokuDB在测试过程中写入稳定性是非常好的
  • 单表容量在InnoDB下1TB+，使用Tokudb的lzma压缩到80GB
  • 独立写程序好一些，与程序解耦方便后期维护
  • 追踪字段值变化可以通过分析row格式binlog好一些
  • 解决了单表过大恢复时间问题，也支持online DDL
  • 物理备份采用xtrabackup热备方案比较好
張 旭

Flynn: first preview release | Hacker News - 0 views

news.ycombinator.com/item

docker consul system service discovery dns

shared by 張 旭 on 25 Nov 15 - No Cached
  • Etcd and Zookeeper provide essentially the same functionality. They are both a strongly consistent key/value stores that support notifications to clients of changes. These two projects are limited to service discovery
  • So lets say you had a client application that would talk to a node application that could be on any number of servers. What you could do is hard code that list into your application and randomly select one, in order to "fake" load balancing. However every time a machine went up or down you would have to update that list.
  • What Consul provides is you just tell your app to connect to "mynodeapp.consul" and then consul will give you the proper address of one of your node apps.
  • ...9 more annotations...
  • Consul and Skydock are both applications that build on top of a tool like Zookeeper and Etcd.
  • What a developer ideally wants to do is just push code and not have to worry about what servers are running what, and worry about failover and the like
  • What Flynn provides (if I get it), is a diy Heroku like platform
  • Another project that I believe may be similar to Flynn is Apache Mesos.
  • a self hosted Heroku
  • Google Omega is Google's answer to Apache Mesos
  • Omega would need a service like Raft to understand what services are currently available
  • Raft is a consensus algorithm for keeping a set of distributed state machines in a consistent state.
  • I want to use Docker, but it has no easy way to say "take this file that contains instructions and make everything". You can write Dockerfiles, but you can only use one part of the stack in them, otherwise you run into trouble.
  • 張 旭 on 25 Nov 15
     
    " So lets say you had a client application that would talk to a node application that could be on any number of servers. What you could do is hard code that list into your application and randomly select one, in order to "fake" load balancing. However every time a machine went up or down you would have to update that list. What Consul provides is you just tell your app to connect to "mynodeapp.consul" and then consul will give you the proper address of one of your node apps."
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

Docker ARG, ENV and .env - a Complete Guide · vsupalov.com - 1 views

vsupalov.com/docker-arg-env-variable-guide

docker development system server environment

shared by 張 旭 on 10 Dec 18 - No Cached
  • understand and use Docker build-time variables, environment variables and docker-compose templating the right way.
  • ARG is only available during the build of a Docker image (RUN etc), not after the image is created and containers are started from it (ENTRYPOINT, CMD).
  • ENV values are available to containers, but also RUN-style commands during the Docker build starting with the line where they are introduced.
  • ...20 more annotations...
  • set an environment variable in an intermediate container using bash (RUN export VARI=5 && …) it will not persist in the next command.
  • An env_file, is a convenient way to pass many environment variables to a single command in one batch.
  • not be confused with a .env file
  • the dot in front of env - .env, not an “env_file”.
  • If you have a file named .env in your project, it’s only used to put values into the docker-compose.yml file which is in the same folder. Those are used with Docker Compose and Docker Stack.
  • Just type docker-compose config. This way you’ll see how the docker-compose.yml file content looks after the substitution step has been performed without running anything else.
  • ARG are also known as build-time variables. They are only available from the moment they are ‘announced’ in the Dockerfile with an ARG instruction up to the moment when the image is built.
  • Running containers can’t access values of ARG variables.
  • ENV variables are also available during the build, as soon as you introduce them with an ENV instruction. However, unlike ARG, they are also accessible by containers started from the final image.
  • ENV values can be overridden when starting a container,
  • If you don’t provide a value to expected ARG variables which don’t have a default, you’ll get an error message.
  • args block
  • You can use ARG to set the default values of ENV vars.
  • dynamic on-build env values
  • 2. Pass environment variable values from your host
  • 1. Provide values one by one
  • 3. Take values from a file (env_file)
  • for each RUN statement, a new container is launched from an intermediate image.
  • An image is saved by the end of the command, but environment variables do not persist that way.
  • The precedence is, from stronger to less-strong: stuff the containerized application sets, values from single environment entries, values from the env_file(s) and finally Dockerfile defaults.
張 旭

Choosing an Executor Type - CircleCI - 0 views

circleci.com/...executor-types

circle CI

shared by 張 旭 on 14 Nov 18 - No Cached
  • Containers are an instance of the Docker Image you specify and the first image listed in your configuration is the primary container image in which all steps run.
  • In this example, all steps run in the container created by the first image listed under the build job
  • If you experience increases in your run times due to installing additional tools during execution, it is best practice to use the Building Custom Docker Images Documentation to create a custom image with tools that are pre-loaded in the container to meet the job requirements.
  • ...9 more annotations...
  • The machine option runs your jobs in a dedicated, ephemeral VM
  • Using the machine executor gives your application full access to OS resources and provides you with full control over the job environment.
  • Using machine may require additional fees in a future pricing update.
  • Using the macos executor allows you to run your job in a macOS environment on a VM.
  • In a multi-image configuration job, all steps are executed in the container created by the first image listed.
  • All containers run in a common network and every exposed port will be available on localhost from a primary container.
  • If you want to work with private images/registries, please refer to Using Private Images.
  • Docker also has built-in image caching and enables you to build, run, and publish Docker images via Remote Docker.
  • if you require low-level access to the network or need to mount external volumes consider using machine
張 旭

Orbs, Jobs, Steps, and Workflows - CircleCI - 0 views

circleci.com/...jobs-steps

circle CI

shared by 張 旭 on 14 Nov 18 - No Cached
  • Orbs are packages of config that you either import by name or configure inline to simplify your config, share, and reuse config within and across projects.
  • Jobs are a collection of Steps.
  • All of the steps in the job are executed in a single unit which consumes a CircleCI container from your plan while it’s running.
  • ...11 more annotations...
  • Workspaces persist data between jobs in a single Workflow.
  • Caching persists data between the same job in different Workflow builds.
  • Artifacts persist data after a Workflow has finished.
  • run using the machine executor which enables reuse of recently used machine executor runs,
  • docker executor which can compose Docker containers to run your tests and any services they require
  • macos executor
  • Steps are a collection of executable commands which are run during a job
  • In addition to the run: key, keys for save_cache:, restore_cache:, deploy:, store_artifacts:, store_test_results: and add_ssh_keys are nested under Steps.
  • checkout: key is required to checkout your code
  • run: enables addition of arbitrary, multi-line shell command scripting
  • orchestrating job runs with parallel, sequential, and manual approval workflows.
張 旭

Internet Gateways - Amazon Virtual Private Cloud - 0 views

docs.aws.amazon.com/...VPC_Internet_Gateway.html

aws networking system

shared by 張 旭 on 10 Jul 18 - No Cached
  • to provide a target in your VPC route tables for internet-routable traffic
  • to perform network address translation (NAT) for instances that have been assigned public IPv4 addresses
  • Ensure that instances in your subnet have a globally unique IP address (public IPv4 address, Elastic IP address, or IPv6 address)
  • ...10 more annotations...
  • To use an internet gateway, your subnet's route table must contain a route that directs internet-bound traffic to the internet gateway.
  • If your subnet is associated with a route table that has a route to an internet gateway, it's known as a public subnet.
  • To enable communication over the internet for IPv4, your instance must have a public IPv4 address or an Elastic IP address that's associated with a private IPv4 address on your instance.
  • Your instance is only aware of the private (internal) IP address space defined within the VPC and subnet
  • internet gateway logically provides the one-to-one NAT on behalf of your instance
  • To enable communication over the internet for IPv6, your VPC and subnet must have an associated IPv6 CIDR block, and your instance must be assigned an IPv6 address from the range of the subnet.
  • When you create a subnet, we automatically associate it with the main route table for the VPC.
  • the main route table doesn't contain a route to an internet gateway
  • Each instance that you launch into a VPC is automatically associated with its default security group.
  • a default security group allow no inbound traffic from the internet and allow all outbound traffic to the internet.
張 旭

Use swarm mode routing mesh | Docker Documentation - 0 views

docs.docker.com/...ingress

docker swarm cluster system server HA networking

shared by 張 旭 on 16 Jun 17 - No Cached
  • Docker Engine swarm mode makes it easy to publish ports for services to make them available to resources outside the swarm.
  • All nodes participate in an ingress routing mesh.
  • routing mesh enables each node in the swarm to accept connections on published ports for any service running in the swarm, even if there’s no task running on the node.
  • ...6 more annotations...
  • Port 7946 TCP/UDP for container network discovery
  • Port 4789 UDP for the container ingress network.
  • When you access port 8080 on any node, the swarm load balancer routes your request to an active container.
  • The routing mesh listens on the published port for any IP address assigned to the node.
  • publish a port for an existing service
  • To use an external load balancer without the routing mesh, set --endpoint-mode to dnsrr instead of the default value of vip
張 旭

VPCs and Subnets - Amazon Virtual Private Cloud - 0 views

docs.aws.amazon.com/...VPC_Subnets.html

aws networking amazon cloud

shared by 張 旭 on 31 Jul 18 - No Cached
  • you must specify a range of IPv4 addresses for the VPC in the form of a Classless Inter-Domain Routing (CIDR) block
  • A VPC spans all the Availability Zones in the region
  • add one or more subnets in each Availability Zone.
  • ...19 more annotations...
  • Each subnet must reside entirely within one Availability Zone and cannot span zones.
  • Availability Zones are distinct locations that are engineered to be isolated from failures in other Availability Zones
  • If a subnet's traffic is routed to an internet gateway, the subnet is known as a public subnet.
  • If a subnet doesn't have a route to the internet gateway, the subnet is known as a private subnet.
  • If a subnet doesn't have a route to the internet gateway, but has its traffic routed to a virtual private gateway for a VPN connection, the subnet is known as a VPN-only subnet.
  • By default, all VPCs and subnets must have IPv4 CIDR blocks—you can't change this behavior.
  • The allowed block size is between a /16 netmask (65,536 IP addresses) and /28 netmask (16 IP addresses).
  • The first four IP addresses and the last IP address in each subnet CIDR block are not available for you to use
  • The allowed block size is between a /28 netmask and /16 netmask
  • The CIDR block must not overlap with any existing CIDR block that's associated with the VPC.
  • Each subnet must be associated with a route table
  • Every subnet that you create is automatically associated with the main route table for the VPC
  • Security groups control inbound and outbound traffic for your instances
  • network ACLs control inbound and outbound traffic for your subnets
  • each subnet must be associated with a network ACL
  • You can create a flow log on your VPC or subnet to capture the traffic that flows to and from the network interfaces in your VPC or subnet.
  • A VPC peering connection enables you to route traffic between the VPCs using private IP addresses
  • you cannot create a VPC peering connection between VPCs that have overlapping CIDR blocks
  • recommend that you create a VPC with a CIDR range large enough for expected future growth, but not one that overlaps with current or expected future subnets anywhere in your corporate or home network, or that overlaps with current or future VPCs
張 旭

Best practices for writing Dockerfiles | Docker Documentation - 0 views

docs.docker.com/...dockerfile_best-practices

docker system

shared by 張 旭 on 28 Sep 18 - No Cached
  • building efficient images
  • Docker builds images automatically by reading the instructions from a Dockerfile -- a text file that contains all commands, in order, needed to build a given image.
  • A Docker image consists of read-only layers each of which represents a Dockerfile instruction.
  • ...47 more annotations...
  • The layers are stacked and each one is a delta of the changes from the previous layer
  • When you run an image and generate a container, you add a new writable layer (the “container layer”) on top of the underlying layers.
  • By “ephemeral,” we mean that the container can be stopped and destroyed, then rebuilt and replaced with an absolute minimum set up and configuration.
  • Inadvertently including files that are not necessary for building an image results in a larger build context and larger image size.
  • To exclude files not relevant to the build (without restructuring your source repository) use a .dockerignore file. This file supports exclusion patterns similar to .gitignore files.
  • minimize image layers by leveraging build cache.
  • if your build contains several layers, you can order them from the less frequently changed (to ensure the build cache is reusable) to the more frequently changed
  • avoid installing extra or unnecessary packages just because they might be “nice to have.”
  • Each container should have only one concern.
  • Decoupling applications into multiple containers makes it easier to scale horizontally and reuse containers
  • Limiting each container to one process is a good rule of thumb, but it is not a hard and fast rule.
  • Use your best judgment to keep containers as clean and modular as possible.
  • do multi-stage builds and only copy the artifacts you need into the final image. This allows you to include tools and debug information in your intermediate build stages without increasing the size of the final image.
  • avoid duplication of packages and make the list much easier to update.
  • When building an image, Docker steps through the instructions in your Dockerfile, executing each in the order specified.
  • the next instruction is compared against all child images derived from that base image to see if one of them was built using the exact same instruction. If not, the cache is invalidated.
  • simply comparing the instruction in the Dockerfile with one of the child images is sufficient.
  • For the ADD and COPY instructions, the contents of the file(s) in the image are examined and a checksum is calculated for each file.
  • If anything has changed in the file(s), such as the contents and metadata, then the cache is invalidated.
  • cache checking does not look at the files in the container to determine a cache match.
  • In that case just the command string itself is used to find a match.
    • 張 旭
      張 旭 on 28 Sep 18
       
      RUN apt-get 這樣的指令，直接比對指令內容的意思。
  • Whenever possible, use current official repositories as the basis for your images.
  • Using RUN apt-get update && apt-get install -y ensures your Dockerfile installs the latest package versions with no further coding or manual intervention.
  • cache busting
  • Docker executes these commands using the /bin/sh -c interpreter, which only evaluates the exit code of the last operation in the pipe to determine success.
  • set -o pipefail && to ensure that an unexpected error prevents the build from inadvertently succeeding.
  • The CMD instruction should be used to run the software contained by your image, along with any arguments.
  • CMD should almost always be used in the form of CMD [“executable”, “param1”, “param2”…]
  • CMD should rarely be used in the manner of CMD [“param”, “param”] in conjunction with ENTRYPOINT
  • The ENV instruction is also useful for providing required environment variables specific to services you wish to containerize,
  • Each ENV line creates a new intermediate layer, just like RUN commands
  • COPY is preferred
  • COPY only supports the basic copying of local files into the container
  • the best use for ADD is local tar file auto-extraction into the image, as in ADD rootfs.tar.xz /
  • If you have multiple Dockerfile steps that use different files from your context, COPY them individually, rather than all at once.
  • using ADD to fetch packages from remote URLs is strongly discouraged; you should use curl or wget instead
  • The best use for ENTRYPOINT is to set the image’s main command, allowing that image to be run as though it was that command (and then use CMD as the default flags).
  • the image name can double as a reference to the binary as shown in the command
  • The VOLUME instruction should be used to expose any database storage area, configuration storage, or files/folders created by your docker container.
  • use VOLUME for any mutable and/or user-serviceable parts of your image
  • If you absolutely need functionality similar to sudo, such as initializing the daemon as root but running it as non-root), consider using “gosu”.
  • always use absolute paths for your WORKDIR
  • An ONBUILD command executes after the current Dockerfile build completes.
  • Think of the ONBUILD command as an instruction the parent Dockerfile gives to the child Dockerfile
  • A Docker build executes ONBUILD commands before any command in a child Dockerfile.
  • Be careful when putting ADD or COPY in ONBUILD. The “onbuild” image fails catastrophically if the new build’s context is missing the resource being added.
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