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Contents contributed and discussions participated by 張 旭

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張 旭

SSH原理与运用 - 0 views

www.ruanyifeng.com/...ssh_remote_login.html

linux ssh key security

shared by 張 旭 on 23 Mar 17 - No Cached
  • SSH是一种网络协议，用于计算机之间的加密登录
  • SSH只是一种协议，存在多种实现，既有商业实现，也有开源实现
  • ssh -p 2222 user@host
  • ...2 more annotations...
  • （1）远程主机收到用户的登录请求，把自己的公钥发给用户。（2）用户使用这个公钥，将登录密码加密后，发送回来。（3）远程主机用自己的私钥，解密登录密码，如果密码正确，就同意用户登录。
  • 不像https协议，SSH协议的公钥是没有证书中心（CA）公证的
張 旭

CertSimple | An nginx config for 2017 - 0 views

certsimple.com/...nx-http2-load-balancing-config

nginx web server performance

shared by 張 旭 on 19 Mar 17 - No Cached
  • HAProxy can't terminate a HTTP/2 connection itself.
  • a server OS which includes OpenSSL 1.02 to have ALPN.
  • a new nginx (anything newer than 1.9.5 supports HTTP/2)
  • ...6 more annotations...
  • we like HTTPS/non-www since HTTPS is needed for current browsers and non-www is short.
  • visit the Mozilla TLS Generator to get the latest cipher suites and TLS versions
  • add the necessary headers for GeoIP and proper logging.
  • HTML5 SSE simpler than websockets
  • nginx -t
  • Scan your site with SSL Labs scan
張 旭

MySQL :: MySQL 5.7 Reference Manual :: 19.2.1.2 Configuring an Instance for Group Repli... - 0 views

dev.mysql.com/...ion-configuring-instances.html

mysql database replication system

shared by 張 旭 on 19 Mar 17 - No Cached
  • store replication metadata in system tables instead of files
  • collect the write set and encode it as a hash using the XXHASH64 hashing algorithm
  • not start operations automatically when the server starts
  • ...10 more annotations...
  • for incoming connections from other members in the group
  • The server listens on this port for member-to-member connections. This port must not be used for user applications at all
  • The loose- prefix used for the group_replication variables above instructs the server to continue to start if the Group Replication plugin has not been loaded at the time the server is started.
  • For example, if each server instance is on a different machine use the IP and port of the machine, such as 10.0.0.1:33061. The recommended port for group_replication_local_address is 33061
  • does not need to list all members in the group
  • The server that starts the group does not make use of this option, since it is the initial server and as such, it is in charge of bootstrapping the group
  • start the bootstrap member first, and let it create the group
  • Creating a group and joining multiple members at the same time is not supported.
  • must only be used on one server instance at any time
  • Disable this option after the first server instance comes online
張 旭

MySQL :: MySQL 5.7 Reference Manual :: 19.1.1.2 Group Replication - 0 views

dev.mysql.com/...group-replication-summary.html

mysql HA system database replication

shared by 張 旭 on 19 Mar 17 - No Cached
  • The replication group is a set of servers that interact with each other through message passing.
  • The communication layer provides a set of guarantees such as atomic message and total order message delivery.
  • a multi-master update everywhere replication protocol
  • ...8 more annotations...
  • a replication group is formed by multiple servers and each server in the group may execute transactions independently
  • Read-only (RO) transactions need no coordination within the group and thus commit immediately
  • any RW transaction the group needs to decide whether it commits or not, thus the commit operation is not a unilateral decision from the originating server
  • when a transaction is ready to commit at the originating server, the server atomically broadcasts the write values (rows changed) and the correspondent write set (unique identifiers of the rows that were updated). Then a global total order is established for that transaction.
  • all servers receive the same set of transactions in the same order
  • The resolution procedure states that the transaction that was ordered first commits on all servers, whereas the transaction ordered second aborts, and thus is rolled back on the originating server and dropped by the other servers in the group. This is in fact a distributed first commit wins rule
  • Group Replication is a shared-nothing replication scheme where each server has its own entire copy of the data
  • MySQL Group Replication protocol
張 旭

MySQL :: MySQL 5.7 Reference Manual :: 19.1 Group Replication Background - 0 views

dev.mysql.com/...up-replication-background.html

mysql cluster HA system database replication

shared by 張 旭 on 19 Mar 17 - No Cached
  • the component can be removed and the system should continue to operate as expected
  • network partitioning
  • split brain scenarios
  • ...8 more annotations...
  • the ultimate challenge is to fuse the logic of the database and data replication with the logic of having several servers coordinated in a consistent and simple way
  • MySQL Group Replication provides distributed state machine replication with strong coordination between servers.
  • Servers coordinate themselves automatically when they are part of the same group
  • The group can operate in a single-primary mode with automatic primary election, where only one server accepts updates at a time.
  • For a transaction to commit, the majority of the group have to agree on the order of a given transaction in the global sequence of transactions
  • Deciding to commit or abort a transaction is done by each server individually, but all servers make the same decision
  • group communication protocols
  • the Paxos algorithm. It acts as the group communication systems engine.
張 旭

MySQL :: MySQL 5.7 Reference Manual :: 20.4 Getting Started with InnoDB Cluster - 0 views

dev.mysql.com/...b-cluster-getting-started.html

mysql cluster HA router database

shared by 張 旭 on 19 Mar 17 - No Cached
  • InnoDB cluster instances are created and managed through the MySQL Shell.
  • To create a new InnoDB cluster, the MySQL Shell must be connected to the MySQL Server instance. By default, this MySQL Server instance is the seed instance of the new InnoDB cluster and hold the initial data set.
  • Sandbox instance are only suitable for deploying and running on your local machine.
  • ...3 more annotations...
  • A minimum of three instances are required to create an InnoDB cluster
  • reverts to read-only mode
  • MySQL Shell provides two scripting languages: JavaScript and Python.
張 旭

MySQL :: MySQL 5.7 Reference Manual :: 20.2 Introducing InnoDB Cluster - 0 views

dev.mysql.com/...nodb-cluster-introduction.html

mysql cluster database HA

shared by 張 旭 on 19 Mar 17 - No Cached
  • A group of MySQL servers can be configured to create a cluster using MySQL Shell
  • The cluster of servers has a single master, called the primary, which acts as the read-write master.
  • Multiple secondary servers are replicas of the master
  • ...6 more annotations...
  • A client application is connected to the primary via MySQL Router
  • MySQL Shell also requires Python 2.7 and above to run cluster provisioning scripts
  • AdminAPI, which enables you to create and administer an InnoDB cluster, using either JavaScript or Python scripting
  • Caches the metadata of the InnoDB cluster and performs high availability routing to the MySQL Server instances which make up the cluster
  • Group Replication mechanism to allow data to be replicated from the primary to the secondaries in the cluster
  • AdminAPI is available as of MySQL Shell 1.0.8.
張 旭

Understanding Nginx HTTP Proxying, Load Balancing, Buffering, and Caching | DigitalOcean - 0 views

www.digitalocean.com/...alancing-buffering-and-caching

nginx proxy networking HA haproxy

shared by 張 旭 on 14 Mar 17 - No Cached
  • allow Nginx to pass requests off to backend http servers for further processing
  • Nginx is often set up as a reverse proxy solution to help scale out infrastructure or to pass requests to other servers that are not designed to handle large client loads
  • explore buffering and caching to improve the performance of proxying operations for clients
  • ...48 more annotations...
  • Nginx is built to handle many concurrent connections at the same time.
  • provides you with flexibility in easily adding backend servers or taking them down as needed for maintenance
  • Proxying in Nginx is accomplished by manipulating a request aimed at the Nginx server and passing it to other servers for the actual processing
  • The servers that Nginx proxies requests to are known as upstream servers.
  • Nginx can proxy requests to servers that communicate using the http(s), FastCGI, SCGI, and uwsgi, or memcached protocols through separate sets of directives for each type of proxy
  • When a request matches a location with a proxy_pass directive inside, the request is forwarded to the URL given by the directive
  • For example, when a request for /match/here/please is handled by this block, the request URI will be sent to the example.com server as http://example.com/match/here/please
  • The request coming from Nginx on behalf of a client will look different than a request coming directly from a client
  • Nginx gets rid of any empty headers
  • Nginx, by default, will consider any header that contains underscores as invalid. It will remove these from the proxied request
    • 張 旭
      張 旭 on 16 Mar 17
       
      這裡要注意一下，header 欄位名稱有設定底線的，要設定 Nginx 讓它可以通過。
  • The "Host" header is re-written to the value defined by the $proxy_host variable.
  • The upstream should not expect this connection to be persistent
  • Headers with empty values are completely removed from the passed request.
  • if your backend application will be processing non-standard headers, you must make sure that they do not have underscores
  • by default, this will be set to the value of $proxy_host, a variable that will contain the domain name or IP address and port taken directly from the proxy_pass definition
  • This is selected by default as it is the only address Nginx can be sure the upstream server responds to
  • (as it is pulled directly from the connection info)
  • $http_host: Sets the "Host" header to the "Host" header from the client request.
  • The headers sent by the client are always available in Nginx as variables. The variables will start with an $http_ prefix, followed by the header name in lowercase, with any dashes replaced by underscores.
  • preference to: the host name from the request line itself
  • set the "Host" header to the $host variable. It is the most flexible and will usually provide the proxied servers with a "Host" header filled in as accurately as possible
  • sets the "Host" header to the $host variable, which should contain information about the original host being requested
  • This variable takes the value of the original X-Forwarded-For header retrieved from the client and adds the Nginx server's IP address to the end.
  • The upstream directive must be set in the http context of your Nginx configuration.
  • http context
  • Once defined, this name will be available for use within proxy passes as if it were a regular domain name
  • By default, this is just a simple round-robin selection process (each request will be routed to a different host in turn)
  • Specifies that new connections should always be given to the backend that has the least number of active connections.
  • distributes requests to different servers based on the client's IP address.
  • mainly used with memcached proxying
  • As for the hash method, you must provide the key to hash against
  • Server Weight
  • Nginx's buffering and caching capabilities
  • Without buffers, data is sent from the proxied server and immediately begins to be transmitted to the client.
  • With buffers, the Nginx proxy will temporarily store the backend's response and then feed this data to the client
  • Nginx defaults to a buffering design
  • can be set in the http, server, or location contexts.
  • the sizing directives are configured per request, so increasing them beyond your need can affect your performance
  • When buffering is "off" only the buffer defined by the proxy_buffer_size directive will be used
  • A high availability (HA) setup is an infrastructure without a single point of failure, and your load balancers are a part of this configuration.
  • multiple load balancers (one active and one or more passive) behind a static IP address that can be remapped from one server to another.
  • Nginx also provides a way to cache content from backend servers
  • The proxy_cache_path directive must be set in the http context.
  • proxy_cache backcache;
    • 張 旭
      張 旭 on 16 Mar 17
       
      這裡的 backcache 是前文設定的 backcache 變數，看起來每個 location 都可以有自己的 cache 目錄。
  • The proxy_cache_bypass directive is set to the $http_cache_control variable. This will contain an indicator as to whether the client is explicitly requesting a fresh, non-cached version of the resource
  • any user-related data should not be cached
  • For private content, you should set the Cache-Control header to "no-cache", "no-store", or "private" depending on the nature of the data
張 旭

Rails Environment Variables · RailsApps - 1 views

railsapps.github.io/ils-environment-variables.html

rails environment system variable

shared by 張 旭 on 13 Mar 17 - No Cached
  • You can pass local configuration settings to an application using environment variables.
  • Operating systems (Linux, Mac OS X, Windows) provide mechanisms to set local environment variables, as does Heroku and other deployment platforms.
  • In general, you shouldn’t save email account credentials or private API keys to a shared git repository.
  • ...10 more annotations...
  • You could “hardcode” your Gmail username and password into the file but that would expose it to everyone who has access to your git repository.
  • It’s important to learn to use the Unix shell if you’re commited to improving your skills as a developer.
  • The gem reads a config/application.yml file and sets environment variables before anything else is configured in the Rails application.
  • make sure this file is listed in the .gitignore file so it isn’t checked into the git repository
  • Rails provides a config.before_configuration
  • YAML.load(File.open(env_file)).each do |key, value| ENV[key.to_s] = value end if File.exists?(env_file)
  • Heroku is a popular choice for low cost, easily configured Rails application hosting.
  • heroku config:add
  • the dotenv Ruby gem
  • Foreman is a tool for starting and configuring multiple processes in a complex application
張 旭

探索 Docker bridge 的正确姿势，亲测有效！ | DaoCloud - 1 views

blog.daocloud.io/docker-bridge

docker networking system

shared by 張 旭 on 10 Mar 17 - No Cached
  • Docker bridge 和 Linux bridge 二者，初看如出一辙，再看又相去甚远
  • Linux bridge 模式下，Linux Kernel 会创建出一个虚拟网桥 ，用以实现主机网络接口与虚拟网络接口间的通信
  • Linux bridge 像一台虚拟交换机
  • ...15 more annotations...
  • Docker Daemon 会创建出一个名为 docker0 的虚拟网桥 ，用来连接宿主机与容器，或者连接不同的容器
  • veth pair 技术的特性可以保证无论哪一个 veth 接收到网络报文，都会无条件地传输给另一方
  • 在桥接模式下，Docker Daemon 将 veth0 附加到 docker0 网桥上，保证宿主机的报文有能力发往 veth0。
  • 将 veth1 添加到 Docker 容器所属的网络命名空间[注释2]，保证宿主机的网络报文若发往 veth0 可以立即被 veth1 收到
  • NATP 包含两种转换方式：SNAT 和 DNAT
  • 目的 NAT (Destination NAT，DNAT): 修改数据包的目的地址
  • 容器的 IP 与端口对外都是不可见的
  • 数据包的目的地址为宿主机的 ip 和端口
  • 将数据包发送附加到 docker0 网桥上的 veth0 接口，veth0 接口再将数据包发送给容器内部的 veth1 接口，容器接收数据包并作出响应
  • 源 NAT (Source NAT，SNAT): 修改数据包的源地址
  • 宿主机上的 docker0 网桥发现数据包的目的地址为外界的 IP 和端口，便会将数据包转发给 eth0 ，并从 eth0 发出去。由于存在 SNAT 规则，会将数据包的源地址转换为宿主机的 ip 和端口
  • Docker 容器对外是不可见的
  • veth pair是用于不同network namespace间进行通信的方式，veth pair 将一个 network namespace 数据发往另一个 network namespace 的 veth
  • 网络命名空间是用于隔离网络资源（/proc/net、IP 地址、网卡、路由等）
  • NAT 为网络地址转换（Network Address Translation）的缩写
張 旭

Rails Database Best Practices - 0 views

blog.carbonfive.com/...rails-database-best-practices

rails database schema system

shared by 張 旭 on 01 Mar 17 - No Cached
  • Databases are extremely feature rich and are really freakin fast when used properly
  • create succinct helpers for accessing subsets of data that are relevant in specific situations
  • Relations are chainable
  • ...24 more annotations...
  • Return an ActiveRecord::Relation
  • Filtering in Ruby is slower
  • Please don't do this
  • trigger the query and therefore, we lose our Relation
  • leaving trivial ordering out of scopes all together.
  • where
  • where
  • .merge() makes it easy to use scopes from other models that have been joined into the query, reducing potential duplication.
  • ActiveRecord provides an easy API for doing many things with our database, but it also makes it pretty easy to do things inefficiently. The layer of abstraction hides what’s really happening.
  • first pure SQL, then ActiveRecord
  • Databases can only do fast lookups for columns with indexes, otherwise it’s doing a sequential scan
  • Add an index on every id column as well as any column that is used in a where clause.
  • use a Query class to encapsulate the potentially gnarly query.
  • subqueries
  • this Query returns an ActiveRecord::Relation
  • where
  • where
  • Single Responsibility Principle
  • Avoid ad-hoc queries outside of Scopes and Query Objects
  • encapsulate data access into scopes and Query objects
  • An ad-hoc query embedded in a controller (or view, task, etc) is harder to test in isolation and cannot be reused
  • to scopes and Query objects
    • 張 旭
      張 旭 on 01 Mar 17
       
      將查詢方式都封裝成 scope 或 query 物件。
  • Every databases provides more datatypes than your ORM might have you believe
  • Both Postgres and MySQL have full-text search capabilities
張 旭

ssl - How to get .pem file from .key and .crt files? - Stack Overflow - 0 views

stackoverflow.com/...em-file-from-key-and-crt-files

https security server nginx apache ssl key

shared by 張 旭 on 22 Feb 17 - No Cached
  • openssl rsa -in server.key -text > private.pem openssl x509 -inform PEM -in server.crt > public.pem
  • A pem file contains the certificate and the private key.
張 旭

certificate - What is a Pem file and how does it differ from other OpenSSL Generated Ke... - 0 views

serverfault.com/...her-openssl-generated-key-file

https security server apache nginx system

shared by 張 旭 on 22 Feb 17 - No Cached
  • Certificate Signing Request.
  • Some applications can generate these for submission to certificate-authorities
  • These get signed by the CA and a certificate is returned
  • ...15 more annotations...
  • The returned certificate is the public certificate (which includes the public key but not the private key), which itself can be in a couple of formats.
  • this is a container format that may include just the public certificate (such as with Apache installs, and CA certificate files /etc/ssl/certs), or may include an entire certificate chain including public key, private key, and root certificates
  • Privacy Enhanced Mail (PEM), a failed method for secure email but the container format it used lives on
  • This is a PEM formatted file containing just the private-key of a specific certificate and is merely a conventional name and not a standardized one.
  • The rights on these files are very important
  • /etc/ssl/private
  • OpenSSL can convert these to .pem
  • .cert .cer .crt A .pem (or rarely .der) formatted file with a different extension
  • there are four different ways to present certificates and their components
  • used preferentially by open-source software
  • It can have a variety of extensions (.pem, .key, .cer, .cert, more)
  • The parent format of PEM
  • a binary version of the base64-encoded PEM file.
  • PEM on it's own isn't a certificate, it's just a way of encoding data
  • X.509 certificates are one type of data that is commonly encoded using PEM.
張 旭

I am a puts debuggerer | Tenderlovemaking - 0 views

tenderlovemaking.com/...i-am-a-puts-debuggerer.html

ruby programming debug rails

shared by 張 旭 on 22 Feb 17 - No Cached
  • method(:render).source_location
  • method(:render).super_method.source_location
  • unbind the method from Kernel, rebind it to the request
  • ...9 more annotations...
  • The TracePoint allocated here will fire on every “call” event and the block will print out the method name and location of the call.
  • The -d flag will enable warnings and also print out every line where an exception was raised.
  • re-raised
  • RUBYOPT=-d bundle exec rake test
  • The RUBYOPT environment variable will get applied to every Ruby program that is executed in this shell, even sub shells executed by rake.
  • @sharing.freeze
  • can't modify frozen Hash
  • where the first mutation happened
  • I hit Ctrl-T (sorry, this only works on OS X, you’ll need to use kill on Linux
張 旭

从达标到卓越 -- API 设计之道 | Taobao FED | 淘宝前端团队 - 0 views

taobaofed.org/...index.html

api system development programming taobao

shared by 張 旭 on 21 Feb 17 - No Cached
  • 高级语言和自然语言（英语）其实相差无几，因此正确地使用（英语的）词法和语法是程序员最基本的素养。
  • 只要能够足够接近人类的日常语言和思维，并且不需要引发额外的大脑思考，那就是易用
  • 词法和语法
  • ...53 more annotations...
  • 语义
  • 版本控制
  • 正确地拼写一个单词是底线
  • 认真地注意 IDE 的 typo 提示（单词拼写错误提示）
  • state 是整个 Component 状态机中的某一个特定状态，既然描述为了状态机，那么状态和状态之间是互相切换的关系。所以对于初始状态，用 initial 来修饰。
  • props 是指 Element 的属性，要么是不存在某个属性值后来为它赋值，要么是存在属性的默认值后来将其覆盖。所以这种行为，default 是合理的修饰词。
  • 成对出现的词应该是：show & hide、open & close。
  • 成对出现的正反义词不可混用
  • 在复数的风格上保持一致，要么所有都是 -s，要么所有都是 -list。
  • 涉及到诸如字典（Dictionary）、表（Map）的时候，不要使用复数！
  • 「map」本身已经包含了这层意思，不需要再用复数去修饰它
  • 最好遵从惯例，使用名词组合 success 和 failure
  • 方法命名用动词
  • 属性命名用名词
  • 布尔值类型用形容词
  • 首字母缩写词的所有字母均大写。（如果某个语言环境有明确的业界惯例，则遵循惯例。）
  • 如果什么都没定，也没业界惯例，那么把单词写全了总是不会错的。
  • React 采用了 componentDidMount 这种过去时风格，而没有使用 componentMounted，从而跟 componentWillMount 形成对照组，方便记忆。
  • 尽量避免使用被动语态。因为被动语态看起来会比较绕，不够直观，因此我们要将被动语态的 API 转换为主动语态。
  • 无论是友好的参数设置，还是让人甜蜜蜜的语法糖，都体现了程序员的人文关怀。
  • 在文件（file）层面同样如此，一个文件只编写一个类，保证文件的职责单一（当然这对很多语言来说是天然的规则）。
  • 将混杂在一个大坨函数中的两件独立事情拆分出去，保证函数（function）级别的职责单一。
  • 现实中的 OOP 编程场景难免触及副作用。
  • 函数本身的运行稳定可预期
  • 函数的运行不对外部环境造成意料外的污染
  • SPM 是阿里通用的埋点统计方案
  • 对外部造成污染一般是两种途径：一是在函数体内部直接修改外部作用域的变量，甚至全局变量；二是通过修改实参间接影响到外部环境，如果实参是引用类型的数据结构。
  • 控制读写权限
  • 优化参数顺序。相关性越高的参数越要前置
  • 可省略的参数后置，以及 为可省略的参数设定缺省值
  • 将可省参数后置同样是最佳实践。
  • 重载（overload）
  • 如果入口参数无法进行有效区分，不要选择重载
  • 根本不明白某个 Boolean 标记位是用来干嘛的，这大大降低了用户的开发体验，以及代码可读性。
    • 張 旭
      張 旭 on 21 Feb 17
       
      我在 ADATA 的 message saver 犯了一樣的錯誤。
  • 同时支持单个和批量的处理，可以降低用户的认知负担。
  • 让 setter 型 API 始终返回 this。这是 jQuery 为我们带来的经典启示 —— 通过返回 this，来产生一种「链式调用（chaining）」的风格
  • 对异步操作都返回一个 Promise
  • 对于一些创造出来的、业务特色的词汇，如果不能用英语简明地翻译，就直接用拼音
  • 一致性可以最大程度降低信息熵
  • 打 log 要么都用中文，要么都用英文。
  • 所有的 setter 操作必须返回 this
  • 「大版本号」即「语义化版本命名」<major>.<minor>.<patch> 中的第一位 <major> 位
  • 接口的扩展方式有很多，比如：继承（extend）、组合（mixin）、装饰（decorate）
  • 在逻辑上确实存在派生关系，并且需要沿用基类行为同时自定义行为的，采用重量级的继承
  • 仅仅是扩充一些行为功能，但是逻辑上压根不存在父子关系的，使用组合
  • 装饰手法更多应用于给定一个接口，将其包装成多种适用于不同场景新接口的情况
  • $.fn.customMethod = function() {};
  • 合理的做法是新增一个 subType 字段
  • 抽象级别一般来说越高越好，将 API 设计成业务无关的，更通用，而且方便扩展
  • 利用多态性（Polymorphism）构建 Consistent APIs。
  • 作为 API 的开发者，一定要提供足够场景适用的 API，来引导我们的用户，不要让他们做出一些出人意料的「妙用」之举
  • 写代码，就像写作，而设计 API 好比列提纲。
  • Think about future, design with flexibility, but only implement for production.
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

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
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