关于Consul(https://www.consul.io)是一个分布式，高可用,支持多数据中心的服务发现和配置共享的服务软件,由 HashiCorp 公司用 Go 语言开发, 基于 Mozilla Public License 2.0 的协议进行开源。 在Consul的文档上，Consul 支持Service Discovery, Health Checking, Key/Value Store, Multi DataCenter。运用Consul,可以在系统中build复杂的应用和服务的发现等。本文不是Consul的学习重点，关于更多Consul的学习，可参考：http://blog.csdn.net/column/details/consul.html

阅读本博客的前提是对Consul中数据中心，节点，服务，健康检查等名词，一些基本的consul命令，Consul UI的使用有一定的了解。

Ocelot对Consul支持是天生集成，在OcelotGateway项目中configuration.json配置就可以开启consul+ocelot的使用，这套组合可以实现什么功能呢？

服务注册，服务发现，API网关(ocelot固有，不作说明)，负载均衡，限流，熔错告警，弹性和瞬态故障处理

一、服务治理：服务注册，服务发现

服务注册和服务发现都是Consul自有的功能，可以通过Consul的http api完成注册或发现，我写了个NuGet库ConsulSharp(https://github.com/axzxs2001/ConsulSharp)，可以在.net core下完成服务的注册和发现，建议服务注册做到一个统一的管理平台里，为了测试方便，可以在Consul的配置文里先配置服务，每次Consul启动时，自动注册；关于服务发现，Ocelot自动可以完成，只需要在OcelotGateway项目中configuration.json进行配置就可以，接下来我们看看怎么配置。

首先下载Consul: https://www.consul.io/downloads.html，本项目是windows下进行测试

再下载Consul配置文件(这个配置文件是适合本例Demo的，可根据具体给你个况调整)https://github.com/axzxs2001/Asp.NetCoreExperiment/tree/master/Asp.NetCoreExperiment/ConsulOcelot/consul

conf文件夹：consul存放配置文件

dist文件夹：consul UI，一个小的consul信息展示门户

data文件夹：consul启动后存放consul的生成的数据和文件，在运行consul前可以清空此文件夹

Consul的配置文件如下：

{"encrypt": "7TnJPB4lKtjEcCWWjN6jSA==","services": [{"id": "API001","name": "API001","tags": [ "API001" ],"address": "192.168.1.99","port": 5001,"checks": [{"id": "API001_Check","name": "API001_Check","http": "http://192.168.1.99:5001/health","interval": "10s","tls_skip_verify": false,"method": "GET","timeout": "1s"}]},{"id": "API002","name": "API002","tags": [ "API002" ],"address": "192.168.1.99","port": 5002,"checks": [{"id": "API002_Check","name": "API002_Check","http": "http://192.168.1.99:5002/health","interval": "10s","tls_skip_verify": false,"method": "GET","timeout": "1s"}]}]}

两个服务API001和API002，跟着两个健康检查API001_Check和API002_Check

基于consul服务的配置，现在创建三个asp.net core web api项目

OcelotGateway，网关项目，端口5000；API001业务API项目，端口5001；业务API项目，API002端口5002，代码参见https://github.com/axzxs2001/Asp.NetCoreExperiment/tree/master/Asp.NetCoreExperiment/ConsulOcelot

OcelotGateway实现引入Ocelot网关，API001,API002实现健康检查的两个get请求。

测试服务注册和发现：

1、 启动consul

consul agent -server -datacenter=dc1 -bootstrap -data-dir ./data -config-file ./conf -ui-dir ./dist -node=n1 -bind 本机IP -client=0.0.0.0

再启动一个consul，查看状态，命令：consul operator raft list-peers

结果：

Node  ID                                    Address            State   Voter  RaftProtocol

n1    dad74de2-173d-1c1e-add0-975a243b59eb  192.168.1.99:8300  leader  true   3

用Consul UI查看

services:

nodes:

可以看到API001和API002服务，并且健康检查都是正常的。

2、 配置Ocelot网关

configuration.json文件如下(关于ocelot配置文件，详见http://ocelot.readthedocs.io/en/latest/features/configuration.html)：

{"ReRoutes": [{"DownstreamPathTemplate": "/api/values","DownstreamScheme": "http","DownstreamHostAndPorts": [{"Host": "localhost","Port": 5001}],"UpstreamPathTemplate": "/api001/values","UpstreamHttpMethod": [ "Get" ],"ServiceName": "API001","LoadBalancer": "RoundRobin","UseServiceDiscovery": true,"ReRouteIsCaseSensitive": false,"QoSOptions": {"ExceptionsAllowedBeforeBreaking": 3,"DurationOfBreak": 10,"TimeoutValue": 5000},"HttpHandlerOptions": {"AllowAutoRedirect": false,"UseCookieContainer": false,"UseTracing": false},"AuthenticationOptions": {"AuthenticationProviderKey": "","AllowedScopes": []},"RateLimitOptions": {"ClientWhitelist": [ "admin" ],"EnableRateLimiting": true,"Period": "1m","PeriodTimespan": 15,"Limit": 5}},{"DownstreamPathTemplate": "/notice","DownstreamScheme": "http","DownstreamHostAndPorts": [{"Host": "localhost","Port": 5001}],"UpstreamPathTemplate": "/notice","UpstreamHttpMethod": [ "Post" ],     "ReRouteIsCaseSensitive": false,"QoSOptions": {"ExceptionsAllowedBeforeBreaking": 3,"DurationOfBreak": 10,"TimeoutValue": 5000},"HttpHandlerOptions": {"AllowAutoRedirect": false,"UseCookieContainer": false,"UseTracing": false},"AuthenticationOptions": {"AuthenticationProviderKey": "","AllowedScopes": []}   },{"DownstreamPathTemplate": "/api/values","DownstreamScheme": "http","DownstreamHostAndPorts": [{"Host": "localhost","Port": 5002}],"UpstreamPathTemplate": "/API002/values","UpstreamHttpMethod": [ "Get" ],"QoSOptions": {"ExceptionsAllowedBeforeBreaking": 3,"DurationOfBreak": 10,"TimeoutValue": 5000},"ServiceName": "API002","LoadBalancer": "RoundRobin","UseServiceDiscovery": true,"HttpHandlerOptions": {"AllowAutoRedirect": false,"UseCookieContainer": false},"AuthenticationOptions": {"AuthenticationProviderKey": "","AllowedScopes": []},"RateLimitOptions": {"ClientWhitelist": [ "user" ],"EnableRateLimiting": true,"Period": "1m","PeriodTimespan": 15,"Limit": 5}}],"GlobalConfiguration": {"ServiceDiscoveryProvider": {"Host": "localhost","Port": 8500},"RateLimitOptions": {"ClientIdHeader": "client_id","QuotaExceededMessage": "Too Many Requests!!!","DisableRateLimitHeaders": false}}}

启动OcelotGateway，API001，API002项目，通过http://localhost:5000/api001/values，和http://localhost:5000/api002/values访问；因为Ocelot配置了Consul的服务治理，所以可以通过配置的服务名称和GlobalConfiguratin的Consul http api接口查找到对应服务的地址，进行访问，这些都是Ocelot帮我们做，这点很容易证明，可以修改Consul配置文件中服务的address为错误IP，就会发现通过5000端口访问不成功。

二、负载均衡

负载均衡需要启动多个API001和API002，才能进行测试，所以发布API001和API002项目，并复制到一个与192.168.1.99在一个局域网的电脑中，同时把Consul和它的配置，UI文件也复制到这台电脑上，网关项目OcelotGateway不需要，假设另外一台电脑为192.168.1.126

首先修改Consul的配置文件如下

{"encrypt": "7TnJPB4lKtjEcCWWjN6jSA==","services": [{"id": "API001","name": "API001","tags": [ "API001" ],"address": "192.168.1.126","port": 5001,"checks": [{"id": "API001_Check","name": "API001_Check","http": "http://192.168.1.126:5001/health","interval": "10s","tls_skip_verify": false,"method": "GET","timeout": "1s"}]},{"id": "API002","name": "API002","tags": [ "API002" ],"address": "192.168.1.126","port": 5002,"checks": [{"id": "API002_Check","name": "API002_Check","http": "http://192.168.1.126:5002/health","interval": "10s","tls_skip_verify": false,"method": "GET","timeout": "1s"}]}]}

在192.168.1.126下启动API001，API002项目

启动consul

consul agent -server -datacenter=dc1 -data-dir ./data -config-file ./conf -ui-dir ./dist -node=n2 -bind 192.168.1.126

同样，在192.168.1.126下用Consul UI查看各服务是否正常

在192.168.1.99下，把192.168.1.126加到集群中，命令如下

consul join 192.168.1.126

注意，consul集群中，consul配置文件中的encrypt，一定要相同，否则无法放加入同一个集群

用consul operator raft list-peers查看状态，会发现n1,n2在一个集群中了

Node  ID                                    Address             State     Voter  RaftProtocol

n1    dad74de2-173d-1c1e-add0-975a243b59eb  192.168.1.99:8300   leader    true   3

n2    efe954ce-9840-5c66-fa80-b9022167d782  192.168.1.126:8300  follower  true   3

些时在浏览器中多次访问view-source:http://localhost:5000/api001/values或view-source:http://localhost:5000/api002/values，会发现返回的内容是交替出现的，因为只有两个相同的API在集群中，这样就实现了负载均衡。

三、限流

限流是通过configuration.json配置完成的，具体值详见http://ocelot.readthedocs.io/en/latest/features/ratelimiting.html

每个要限流Route中

    "RateLimitOptions": {"ClientWhitelist": [ "admin" ],"EnableRateLimiting": true,"Period": "1m","PeriodTimespan": 15,"Limit": 5}

GlobalConfiguration中"RateLimitOptions": {"ClientIdHeader": "client_id","QuotaExceededMessage": "too more request","DisableRateLimitHeaders": false}

需要说明的是如果配置ClientWithelist白名单，需要在访问api的客户端添加一个Header项目，key为client_id，值为admin，此客户端就不受限流控制

为了测试限流创建 TestClient控制台程序进行测试，交果如下图，在一分钟内，用adminclinet访问API001超过五次也可以，访问API002，只能五次

四、熔错告警

熔断保护在Consul中和Ocelot中都有实现，意义当一个服务不正常时，首先不影响正常使用(因为服务作了集群，可以把请求转到别的服务器上)，二是发生问题，应该用所告警。Ocelot负载均衡可以自动发现服务出问题(Consul有健检查)，并停止对异常服务请求；告警是通过Consul配置文件实现的，关于watches参看https://www.consul.io/docs/agent/watches.html

{"watches": [{"type": "checks","handler_type": "http","state": "critical","http_handler_config": {"path": "http://192.168.1.99:5000/notice","method": "POST","timeout": "10s","header": { "Authorization": [ "token" ] }}}]}

在consul启动时，会加载conf下的所有json文件，因为是json内容是watches节点，consul会作特定处理。

同时http://192.168.1.99:5000/notice映射的http://localhost:5001/notice中作了一个发邮件的操作，把发生异常的服务信息发送给对应邮箱，这里注意，测试时，不要关了API001测试，因为发邮件的功能在这个项目里，可以关掉API002测试，真实环境中，这块肯定是独立项目处理，并且采用集群的，效果如下：

关掉192.168.1.99下的API2，作业报警邮件会提示准确的检查错误和服务名称。

五、弹性和瞬态故障处理

弹性和瞬态故障处理，是Ocelot内置的功能，在网关转发每个请求时，会用Polly(https://github.com/App-vNext/Polly)处理，设置详见http://ocelot.readthedocs.io/en/latest/features/qualityofservice.html，开发上不作任何处理。