Java中间件-Zuul（Java中间件是什么意思）

一、zuul简介

1、作用

zuul使用一系列的filter实现以下功能

认证和安全 - 对每一个resource进行身份认证

追踪和监控 - 实时观察后端微服务的TPS、响应时间，失败数量等准确的信息

日志 - 记录所有请求的访问日志数据，可以为日志分析和查询提供统一支持

动态路由 - 动态的将request路由到后端的服务上去

压力测试 - 逐渐的增加访问集群的压力，来测试集群的性能

限流 - allocating capacity for each type of request and dropping requests that go over the limit

静态响应 - 直接在网关返回一些响应，而不是通过内部的服务返回响应

2、组件：

zuul-core ：library which contains the core functionality of compiling and executing Filters

zuul-netflix ：library which adds other NetflixOSS components to Zuul - using Ribbon for routing requests, for example.

3、例子：

zuul-simple-webapp ：webapp which shows a simple example of how to build an application with zuul-core

zuul-netflix-webapp ：webapp which packages zuul-core and zuul-netflix together into an easy to use package

github地址：https://github.com/Netflix/zuul/

二、zuul filter

1、关键元素

Type ：most often defines the stage during the routing flow when the Filter will be applied (although it can be any custom string)

值可以是：pre、route、post、error、custom

Execution Order : filter执行的顺序(applied within the Type, defines the order of execution across multiple Filters)

Criteria ：filter执行的条件(the conditions required in order for the Filter to be executed)

Action : filter执行的动作(the action to be executed if the Criteria is met)

注意点：

filters之间不会直接进行通讯交流，他们通过一个RequestContext共享一个state

该RequestContext对于每一个request都是唯一的

filter当前使用groovy来写的，也可以使用java

The source code for each Filter is written to a specified set of directories on the Zuul server that are periodically polled for changes

zuul可以动态的read, compile, and run these Filters

被更新后的filter会被从disk读取到内存，并动态编译到正在运行的server中，之后可以用于其后的每一个请求(Updated filters are read from disk, dynamically compiled into the running server, and are invoked by Zuul for each subsequent request)

2、filter type(与一个典型的request的生命周期相关的filter type)

PRE Filters

执行时机： before routing to the origin.

这类filter可能做的事

request authentication

choosing origin servers(选机器)

logging debug info.

限流

ROUTING Filters

这类filter可能做的事：真正的向service的一台server(这台server是pre filter选出来的)发请求，handle routing the request to an origin，This is where the origin HTTP request is built and sent using Apache HttpClient or Netflix Ribbon.

POST Filters

执行时机：after the request has been routed to the origin

这类filter可能做的事

adding standard HTTP headers to the response

gathering statistics and metrics

streaming the response from the origin to the client

ERROR Filters

执行时机：其他三个阶段任一阶段发生错误时执行(when an error occurs during one of the other phases)

CUSTOM Filters

沿着默认的filter流，zuul允许我们创建一些自定义的Filter type，并且准确的执行他们。

例如：我们自定义一个STATIC type的filter，用于从zuul直接产生响应，而不是从后边的services(we have a custom STATIC type that generates a response within Zuul instead of forwarding the request to an origin)

三、zuul request lifecycle(filter流)

说明：对应(二)的filter type来看

四、zuul核心架构

zuul的核心就是：filter、filter流与核心架构。