Consul 是 HashiCorp 公司推出的开源工具，用于实现分布式系统的服务发现与配置。与其他分布式服务注册与发现的方案，Consul的方案更“一站式” ，内置了服务注册与发现框架

介绍

据说使用起来也较为简单。Consul使用Go语言编写，因此具有天然可移植性(支持Linux、windows和Mac OS X)；安装包仅包含一个可执行文件，方便部署，与Docker等轻量级容器可无缝配合。基于 Mozilla Public License 2.0 的协议进行开源. Consul 支持健康检查,并允许 HTTP 和 DNS 协议调用 API 存储键值对. 一致性协议采用 Raft 算法,用来保证服务的高可用. 使用 GOSSIP 协议管理成员和广播消息, 并且支持 ACL 访问控制.

Consul 四大特性

Service Discovery (服务发现)
Health Check (健康检查)
Multi Datacenter (多数据中心)
Key/Value Storage

Consul Glossary(术语)

Agent

Agent 是一个守护进程
运行在Consul集群的每个成员上
有Client 和 Server 两种模式
所有Agent都可以被调用DNS或者HTTP API,并负责检查和维护同步

Client

Client 将所有RPC请求转发至Server
Client 是相对无状态的
Client 唯一做的就是参与LAN Gossip Pool
Client 只消耗少量的资源和少量的网络带宽

Server

参与 Raft quorum(一致性判断)
响应RPC查询请求
维护集群的状态
转发查询到Leader 或远程数据中心

Datacenter

顾名思义其为数据中心, 如何定义数据中心呢? 需要以下三点

私有的
低延迟
高带宽
故: 可以简单的理解为同属一个内网环境, 如北京机房和香港机房就不一定满足以上三个条件

Consensus (一致性)

Consul 使用consensus protocol 来提供CAP(一致性,高可用,分区容错性)

Gossip

一种协议: 用来保证最终一致性 , 即: 无法保证在某个时刻, 所有节点状态一致, 但可以保证”最终”一致

LAN Gossip

Local Area Network Gossip, 位于同一个局域网或者数据中心的节点

WAN Gossip

Wide Area Network Gossip, 只用于Server之间, 分部在不同的数据中心或广域网

构架图

安装Consul

下载地址：https://www.consul.io/downloads.html

各种平台的都有下载：Mac OS X、FreeBSD、Linux、Solaris、Windows

我是在mac上使用，所以下了个mac版本的

下过来的zip，解压以后得到一个单独二级制文件，我把它直接放到了/usr/local/bin下

这样，在控制台中，我就直接能使用了，可以使用以下命令，来测试是否可运行

$ consul -v
Consul v1.0.3
Protocol 2 spoken by default, understands 2 to 3 (agent will automatically use protocol >2 when speaking to compatible agents)

以调试模式启动Consul

可以用下面的命令启动Consul的开发模式：

$ consul agent -dev
==> Starting Consul agent...
==> Consul agent running!
           Version: 'v1.0.3'
           Node ID: 'aef05660-c518-c124-f8bd-e2e8148b0fa2'
         Node name: 'zhangxiaodeMacBook-Pro.local'
        Datacenter: 'dc1' (Segment: '<all>')
            Server: true (Bootstrap: false)
       Client Addr: [127.0.0.1] (HTTP: 8500, HTTPS: -1, DNS: 8600)
      Cluster Addr: 127.0.0.1 (LAN: 8301, WAN: 8302)
           Encrypt: Gossip: false, TLS-Outgoing: false, TLS-Incoming: false

==> Log data will now stream in as it occurs:

    2018/02/03 15:37:32 [DEBUG] Using random ID "aef05660-c518-c124-f8bd-e2e8148b0fa2" as node ID
    2018/02/03 15:37:32 [INFO] raft: Initial configuration (index=1): [{Suffrage:Voter ID:aef05660-c518-c124-f8bd-e2e8148b0fa2 Address:127.0.0.1:8300}]
    2018/02/03 15:37:32 [INFO] raft: Node at 127.0.0.1:8300 [Follower] entering Follower state (Leader: "")
    2018/02/03 15:37:32 [INFO] serf: EventMemberJoin: zhangxiaodeMacBook-Pro.local.dc1 127.0.0.1
    2018/02/03 15:37:32 [INFO] serf: EventMemberJoin: zhangxiaodeMacBook-Pro.local 127.0.0.1
    2018/02/03 15:37:32 [INFO] consul: Handled member-join event for server "zhangxiaodeMacBook-Pro.local.dc1" in area "wan"
    2018/02/03 15:37:32 [INFO] consul: Adding LAN server zhangxiaodeMacBook-Pro.local (Addr: tcp/127.0.0.1:8300) (DC: dc1)
    2018/02/03 15:37:32 [INFO] agent: Started DNS server 127.0.0.1:8600 (udp)
    2018/02/03 15:37:32 [INFO] agent: Started DNS server 127.0.0.1:8600 (tcp)
    2018/02/03 15:37:32 [INFO] agent: Started HTTP server on 127.0.0.1:8500 (tcp)
    2018/02/03 15:37:32 [INFO] agent: started state syncer
    2018/02/03 15:37:32 [WARN] raft: Heartbeat timeout from "" reached, starting election
    2018/02/03 15:37:32 [INFO] raft: Node at 127.0.0.1:8300 [Candidate] entering Candidate state in term 2
    2018/02/03 15:37:32 [DEBUG] raft: Votes needed: 1
    2018/02/03 15:37:32 [DEBUG] raft: Vote granted from aef05660-c518-c124-f8bd-e2e8148b0fa2 in term 2. Tally: 1
    2018/02/03 15:37:32 [INFO] raft: Election won. Tally: 1
    2018/02/03 15:37:32 [INFO] raft: Node at 127.0.0.1:8300 [Leader] entering Leader state
    2018/02/03 15:37:32 [INFO] consul: cluster leadership acquired
    2018/02/03 15:37:32 [INFO] consul: New leader elected: zhangxiaodeMacBook-Pro.local
    2018/02/03 15:37:32 [DEBUG] consul: Skipping self join check for "zhangxiaodeMacBook-Pro.local" since the cluster is too small
    2018/02/03 15:37:32 [INFO] consul: member 'zhangxiaodeMacBook-Pro.local' joined, marking health alive
    2018/02/03 15:37:33 [DEBUG] Skipping remote check "serfHealth" since it is managed automatically
    2018/02/03 15:37:33 [INFO] agent: Synced node info
    2018/02/03 15:37:33 [DEBUG] agent: Node info in sync
    2018/02/03 15:37:33 [DEBUG] Skipping remote check "serfHealth" since it is managed automatically
    2018/02/03 15:37:33 [DEBUG] agent: Node info in sync
    2018/02/03 15:37:38 [DEBUG] http: Request GET /v1/event/list?wait=5s&index=1 (5.001249189s) from=127.0.0.1:54222

启动一个开发模式的consul非常简单
但是在生产环境，我想并没有这么简单，后面再深入了解下

现在访问下：http://localhost:8500 ，可以看到consul的ui界面

docker-compose 参考

version: "2"
services:
  app1:
    build: ./python_app/
    ports:
      - "8080:8080"
  app2:
    build: ./python_app/
    ports:
      - "8081:8080"
  consul1:
    image: "progrium/consul:latest"
    container_name: "consul1"
    hostname: "consul1"
    ports:
      - "8400:8400"
      - "8500:8500"
      - "8600:53"
    command: "-server -bootstrap-expect 3 -ui-dir /ui"
  consul2:
    image: "progrium/consul:latest"
    container_name: "consul2"
    hostname: "consul2"
    expose:
      - "8400"
      - "8500"
      - "8600"
    command: "-server -join consul1"
    depends_on:
      - consul1
  consul3:
    image: "progrium/consul:latest"
    container_name: "consul3"
    hostname: "consul3"
    expose:
      - "8400"
      - "8500"
      - "8600"
    command: "-server -join consul1"
    depends_on:
      - consul1

参考文章

《Install Consul》
《Spring Cloud构建微服务架构：服务注册与发现（Eureka、Consul）【Dalston版】》
《服务注册发现consul之一：spring cloud consul介绍及安装》
《Introduction to Consul》
《现有系统如何集成Consul服务发现》