SSH是一种网络协议，用于计算机之间的加密登录
Creating a Custom Rails Environment - RichOnRails.com - 0 views
SSH原理与运用（二）：远程操作与端口转发 - 阮一峰的网络日志 - 0 views
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SSH原理与运用 - 0 views
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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
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ssh -p 2222 user@host
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（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。
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不像https协议，SSH协议的公钥是没有证书中心（CA）公证的
Redesigning Evernote for iOS - Evernote Design - Medium - 0 views
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CertSimple | An nginx config for 2017 - 0 views
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HAProxy can't terminate a HTTP/2 connection itself.
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a server OS which includes OpenSSL 1.02 to have ALPN.
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a new nginx (anything newer than 1.9.5 supports HTTP/2)
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we like HTTPS/non-www since HTTPS is needed for current browsers and non-www is short.
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visit the Mozilla TLS Generator to get the latest cipher suites and TLS versions
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add the necessary headers for GeoIP and proper logging.
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HTML5 SSE simpler than websockets
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nginx -t
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Scan your site with SSL Labs scan
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MySQL :: MySQL 5.7 Reference Manual :: 19.2.1.2 Configuring an Instance for Group Repli... - 0 views
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store replication metadata in system tables instead of files
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collect the write set and encode it as a hash using the XXHASH64 hashing algorithm
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not start operations automatically when the server starts
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for incoming connections from other members in the group
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The server listens on this port for member-to-member connections. This port must not be used for user applications at all
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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.
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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
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does not need to list all members in the group
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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
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start the bootstrap member first, and let it create the group
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Creating a group and joining multiple members at the same time is not supported.
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must only be used on one server instance at any time
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Disable this option after the first server instance comes online
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MySQL :: MySQL 5.7 Reference Manual :: 19.1.1.2 Group Replication - 0 views
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The replication group is a set of servers that interact with each other through message passing.
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The communication layer provides a set of guarantees such as atomic message and total order message delivery.
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a multi-master update everywhere replication protocol
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a replication group is formed by multiple servers and each server in the group may execute transactions independently
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Read-only (RO) transactions need no coordination within the group and thus commit immediately
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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
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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.
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all servers receive the same set of transactions in the same order
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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
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Group Replication is a shared-nothing replication scheme where each server has its own entire copy of the data
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MySQL Group Replication protocol
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MySQL :: MySQL 5.7 Reference Manual :: 19.1 Group Replication Background - 0 views
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the component can be removed and the system should continue to operate as expected
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network partitioning
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split brain scenarios
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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
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MySQL Group Replication provides distributed state machine replication with strong coordination between servers.
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Servers coordinate themselves automatically when they are part of the same group
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The group can operate in a single-primary mode with automatic primary election, where only one server accepts updates at a time.
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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
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Deciding to commit or abort a transaction is done by each server individually, but all servers make the same decision
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group communication protocols
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the Paxos algorithm. It acts as the group communication systems engine.
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MySQL :: MySQL 5.7 Reference Manual :: 20.4 Getting Started with InnoDB Cluster - 0 views
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InnoDB cluster instances are created and managed through the MySQL Shell.
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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.
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Sandbox instance are only suitable for deploying and running on your local machine.
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A minimum of three instances are required to create an InnoDB cluster
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reverts to read-only mode
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MySQL Shell provides two scripting languages: JavaScript and Python.
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MySQL :: MySQL 5.7 Reference Manual :: 20.2 Introducing InnoDB Cluster - 0 views
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A group of MySQL servers can be configured to create a cluster using MySQL Shell
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The cluster of servers has a single master, called the primary, which acts as the read-write master.
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Multiple secondary servers are replicas of the master
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A client application is connected to the primary via MySQL Router
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MySQL Shell also requires Python 2.7 and above to run cluster provisioning scripts
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AdminAPI, which enables you to create and administer an InnoDB cluster, using either JavaScript or Python scripting
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Caches the metadata of the InnoDB cluster and performs high availability routing to the MySQL Server instances which make up the cluster
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Group Replication mechanism to allow data to be replicated from the primary to the secondaries in the cluster
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AdminAPI is available as of MySQL Shell 1.0.8.
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Understanding Nginx HTTP Proxying, Load Balancing, Buffering, and Caching | DigitalOcean - 0 views
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allow Nginx to pass requests off to backend http servers for further processing
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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
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explore buffering and caching to improve the performance of proxying operations for clients
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Nginx is built to handle many concurrent connections at the same time.
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provides you with flexibility in easily adding backend servers or taking them down as needed for maintenance
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Proxying in Nginx is accomplished by manipulating a request aimed at the Nginx server and passing it to other servers for the actual processing
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The servers that Nginx proxies requests to are known as upstream servers.
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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
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When a request matches a location with a proxy_pass directive inside, the request is forwarded to the URL given by the directive
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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
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The request coming from Nginx on behalf of a client will look different than a request coming directly from a client
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Nginx gets rid of any empty headers
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Nginx, by default, will consider any header that contains underscores as invalid. It will remove these from the proxied request
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The "Host" header is re-written to the value defined by the $proxy_host variable.
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The upstream should not expect this connection to be persistent
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Headers with empty values are completely removed from the passed request.
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if your backend application will be processing non-standard headers, you must make sure that they do not have underscores
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by default, this will be set to the value of $proxy_host, a variable that will contain the domain name or IP address and port taken directly from the proxy_pass definition
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This is selected by default as it is the only address Nginx can be sure the upstream server responds to
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(as it is pulled directly from the connection info)
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$http_host: Sets the "Host" header to the "Host" header from the client request.
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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.
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preference to: the host name from the request line itself
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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
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sets the "Host" header to the $host variable, which should contain information about the original host being requested
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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.
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The upstream directive must be set in the http context of your Nginx configuration.
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http context
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Once defined, this name will be available for use within proxy passes as if it were a regular domain name
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By default, this is just a simple round-robin selection process (each request will be routed to a different host in turn)
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Specifies that new connections should always be given to the backend that has the least number of active connections.
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distributes requests to different servers based on the client's IP address.
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mainly used with memcached proxying
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As for the hash method, you must provide the key to hash against
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Server Weight
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Nginx's buffering and caching capabilities
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Without buffers, data is sent from the proxied server and immediately begins to be transmitted to the client.
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With buffers, the Nginx proxy will temporarily store the backend's response and then feed this data to the client
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Nginx defaults to a buffering design
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can be set in the http, server, or location contexts.
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the sizing directives are configured per request, so increasing them beyond your need can affect your performance
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When buffering is "off" only the buffer defined by the proxy_buffer_size directive will be used
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A high availability (HA) setup is an infrastructure without a single point of failure, and your load balancers are a part of this configuration.
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multiple load balancers (one active and one or more passive) behind a static IP address that can be remapped from one server to another.
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Nginx also provides a way to cache content from backend servers
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The proxy_cache_path directive must be set in the http context.
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proxy_cache backcache;
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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
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any user-related data should not be cached
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For private content, you should set the Cache-Control header to "no-cache", "no-store", or "private" depending on the nature of the data
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Laptop USB Console Adapter - CV211, ATEN KVM Cables - 0 views
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" 'Turn your laptop into a mobile console in a few seconds.' The CV211 Laptop USB Console Adapter provides a direct Laptop-to-Computer connection for fast and easy remote desktop access with no software to install. High efficiency in a compact design, the CV211 offers bi-directional file transfers, hotkey macros, video recording and screenshots through a USB 2.0 and VGA composite cable."
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Rails Environment Variables · RailsApps - 1 views
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You can pass local configuration settings to an application using environment variables.
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Operating systems (Linux, Mac OS X, Windows) provide mechanisms to set local environment variables, as does Heroku and other deployment platforms.
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In general, you shouldn’t save email account credentials or private API keys to a shared git repository.
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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.
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It’s important to learn to use the Unix shell if you’re commited to improving your skills as a developer.
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The gem reads a config/application.yml file and sets environment variables before anything else is configured in the Rails application.
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make sure this file is listed in the .gitignore file so it isn’t checked into the git repository
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Rails provides a config.before_configuration
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YAML.load(File.open(env_file)).each do |key, value| ENV[key.to_s] = value end if File.exists?(env_file)
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Heroku is a popular choice for low cost, easily configured Rails application hosting.
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heroku config:add
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the dotenv Ruby gem
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Foreman is a tool for starting and configuring multiple processes in a complex application
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探索 Docker bridge 的正确姿势，亲测有效！ | DaoCloud - 1 views
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Docker bridge 和 Linux bridge 二者，初看如出一辙，再看又相去甚远
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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
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Linux bridge 像一台虚拟交换机
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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
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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
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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。
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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
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NATP 包含两种转换方式：SNAT 和 DNAT
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目的 NAT (Destination NAT，DNAT): 修改数据包的目的地址
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容器的 IP 与端口对外都是不可见的
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数据包的目的地址为宿主机的 ip 和端口
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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
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源 NAT (Source NAT，SNAT): 修改数据包的源地址
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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
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Docker 容器对外是不可见的
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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
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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）
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NAT 为网络地址转换（Network Address Translation）的缩写
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Rails Routing from the Outside In - Ruby on Rails Guides - 0 views
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Resource routing allows you to quickly declare all of the common routes for a given resourceful controller.
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Rails would dispatch that request to the destroy method on the photos controller with { id: '17' } in params.
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a resourceful route provides a mapping between HTTP verbs and URLs to controller actions.
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each action also maps to particular CRUD operations in a database
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resource :photo and resources :photos creates both singular and plural routes that map to the same controller (PhotosController).
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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.
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to only build routes with the minimal amount of information to uniquely identify the resource
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The shallow method of the DSL creates a scope inside of which every nesting is shallow
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These concerns can be used in resources to avoid code duplication and share behavior across routes
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add a member route, just add a member block into the resource block
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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].
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Singular Resources
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use a singular resource to map /profile (rather than /profile/:id) to the show action
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Passing a String to get will expect a controller#action format
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workaround
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organize groups of controllers under a namespace
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route /articles (without the prefix /admin) to Admin::ArticlesController
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route /admin/articles to ArticlesController (without the Admin:: module prefix)
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Nested routes allow you to capture this relationship in your routing.
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helpers take an instance of Magazine as the first parameter (magazine_ads_url(@magazine)).
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Resources should never be nested more than 1 level deep.
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via the :shallow option
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a balance between descriptive routes and deep nesting
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:shallow_path prefixes member paths with the specified parameter
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Routing Concerns allows you to declare common routes that can be reused inside other resources and routes
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Rails can also create paths and URLs from an array of parameters.
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use url_for with a set of objects
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In helpers like link_to, you can specify just the object in place of the full url_for call
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insert the action name as the first element of the array
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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.
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pass :on to a route, eliminating the block:
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Collection Routes
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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.
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simple routing makes it very easy to map legacy URLs to new Rails actions
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add an alternate new action using the :on shortcut
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When you set up a regular route, you supply a series of symbols that Rails maps to parts of an incoming HTTP request.
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:controller maps to the name of a controller in your application
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:action maps to the name of an action within that controller
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optional parameters, denoted by parentheses
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This route will also route the incoming request of /photos to PhotosController#index, since :action and :id are
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use a constraint on :controller that matches the namespace you require
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dynamic segments don't accept dots
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The params will also include any parameters from the query string
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:defaults option.
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set params[:format] to "jpg"
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cannot override defaults via query parameters
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specify a name for any route using the :as option
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create logout_path and logout_url as named helpers in your application.
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Inside the show action of UsersController, params[:username] will contain the username for the user.
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should use the get, post, put, patch and delete methods to constrain a route to a particular verb.
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use the match method with the :via option to match multiple verbs at once
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Routing both GET and POST requests to a single action has security implications
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'GET' in Rails won't check for CSRF token. You should never write to the database from 'GET' requests
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use the :constraints option to enforce a format for a dynamic segment
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constraints
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don't need to use anchors
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Request-Based Constraints
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the same name as the hash key and then compare the return value with the hash value.
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constraint values should match the corresponding Request object method return type
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blacklist
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redirect helper
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reuse dynamic segments from the match in the path to redirect
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this redirection is a 301 "Moved Permanently" redirect.
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root method
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put the root route at the top of the file
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The root route only routes GET requests to the action.
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root inside namespaces and scopes
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For namespaced controllers you can use the directory notation
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Only the directory notation is supported
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use the :constraints option to specify a required format on the implicit id
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specify a single constraint to apply to a number of routes by using the block
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non-resourceful routes
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:id parameter doesn't accept dots
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:as option lets you override the normal naming for the named route helpers
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use the :as option to prefix the named route helpers that Rails generates for a rout
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prevent name collisions
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prefix routes with a named parameter
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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
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:only option
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:except option
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generate only the routes that you actually need can cut down on memory use and speed up the routing process.
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alter path names
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http://localhost:3000/rails/info/routes
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rake routes
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setting the CONTROLLER environment variable
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Routes should be included in your testing strategy
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assert_generates assert_recognizes assert_routing
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Rails Database Best Practices - 0 views
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Databases are extremely feature rich and are really freakin fast when used properly
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create succinct helpers for accessing subsets of data that are relevant in specific situations
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Relations are chainable
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Return an ActiveRecord::Relation
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Filtering in Ruby is slower
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Please don't do this
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trigger the query and therefore, we lose our Relation
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leaving trivial ordering out of scopes all together.
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where
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where
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.merge() makes it easy to use scopes from other models that have been joined into the query, reducing potential duplication.
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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.
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first pure SQL, then ActiveRecord
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Databases can only do fast lookups for columns with indexes, otherwise it’s doing a sequential scan
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Add an index on every id column as well as any column that is used in a where clause.
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use a Query class to encapsulate the potentially gnarly query.
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subqueries
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this Query returns an ActiveRecord::Relation
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where
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where
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Single Responsibility Principle
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Avoid ad-hoc queries outside of Scopes and Query Objects
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encapsulate data access into scopes and Query objects
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An ad-hoc query embedded in a controller (or view, task, etc) is harder to test in isolation and cannot be reused
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to scopes and Query objects
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Every databases provides more datatypes than your ORM might have you believe
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Both Postgres and MySQL have full-text search capabilities
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