基于Consul的数据库高可用架构

Posted 2020-10-31 hch的随笔成功的秘诀在于恒心—迪斯雷利

tags:

篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了基于Consul的数据库高可用架构相关的知识，希望对你有一定的参考价值。

几个月没有更新博客了，已经长草了，特意来除草。本次主要分享如何利用consul来实现redis以及mysql的高可用。以前的公司mysql是单机单实例，高可用MHA加vip就能搞定，新公司mysql是单机多实例，那么显然这个方案不适用，后来也实现了故障切换调用dns api来修改域名记录，但是还是没有利用consul来实现高可用方便，后面会说明优势。redis单机多实例最正常不过了，那么redis单机多实例高可用也不太好做，当然也可以利用sentinel来实现，当failover以后调用脚本调用dns api修改域名解析也是可以的。也不是那么的优雅，有人会说怎么不用codis，redis cluster，这些方案固然好，但不适合我们，这些方案不够灵活，不能很好的处理热点数据的问题。那么consul是什么呢，接下慢慢说：

consul是HashiCorp公司（曾经开发过vgrant）推出的一款开源工具，基于go语言开发，轻量级，用于实现分布式系统的服务发现与配置。与其他类似产品相比，提供更“一站式”的解决方案。 consul内置有KV存储，服务注册/发现，健康检查， HTTP+DNS API， Web UI等多种功能。官网： https://www.consul.io/其他同类服务发现与配置的主流开源产品有:zookeeper和ETCD。

consul的优势：

1. 支持多数据中心，内外网的服务采用不同的端口进行监听。多数据中心集群可以避免单数据中心的单点故障, zookeeper和 etcd 均不提供多数据中心功能的支持

2. 支持健康检查. etcd 不提供此功能.

3. 支持 http 和 dns 协议接口. zookeeper 的集成较为复杂,etcd 只支持 http 协议. 有DNS功能，支持REST API

4. 官方提供web管理界面, etcd 无此功能.

5. 部署简单，运维友好，无依赖， go的二进制程序copy过来就能用了，一个程序搞定，可以结合ansible来推送。

Consul和其他服务发现工具的对比表：

Consul 架构和角色

1. Consul Cluster由部署和运行了Consul Agent的节点组成。在Cluster中有两种角色:Server和 Client。
2. Server和Client的角色和Consul Cluster上运行的应用服务无关, 是基于Consul层面的一种角色划分.
3. Consul Server: 用于维护Consul Cluster的状态信息，实现数据一致性，响应RPC请求。官方建议是: 至少要运行3个或者3个以上的Consul Server。多个server之中需要选举一个leader, 这个选举过程Consul基于Raft协议实现. 多个Server节点上的Consul数据信息保持强一致性。在局域网内与本地客户端通讯，通过广域网与其他数据中心通讯。Consul Client: 只维护自身的状态, 并将HTTP和DNS接口请求转发给服务端。
4. Consul 支持多数据中心，多个数据中心要求每个数据中心都要安装一组Consul cluster，多个数据中心间基于gossip protocol协议来通讯，使用Raft算法实现一致性

基础知识就介绍这么多了，更加详细的可以参考官网。下面我们来搭建一下consul，以及如何利用consul实现redis以及mysql的高可用。

测试环境（生产环境consul server部署3个或者5个）：

consul server：192.168.0.10

consul client：192.168.0.20，192.168.0.30，192.168.0.40

consul的安装非常容易，从https://www.consul.io/downloads.html这里下载以后，解压即可使用，就是一个二进制文件，其他的都没有了。我这里使用的是0.92版本。文件下载以后解压放到/usr/local/bin。就可以使用了。不依赖任何东西。上面的4台服务器都安装。

4台机器都创建目录，分别是放配置文件，以及存放数据的。以及存放redis，mysql的健康检查脚本

mkdir /etc/consul.d/ -p && mkdir /data/consul/ -p

mkidr /data/consul/shell -p

然后把相关配置参数写入配置文件，其实也可以不用写，直接跟在命令后面就行，那样不方便管理。
consul server（192.168.0.10）配置文件（具体参数的意思请查询官网或者文章给的参考链接）：

[root@db-server-yayun-01 ~]# cat /etc/consul.d/server.json 
{
  "data_dir": "/data/consul",
  "datacenter": "dc1",
  "log_level": "INFO",
  "server": true,
  "bootstrap_expect": 1,
  "bind_addr": "192.168.0.10",
  "client_addr": "192.168.0.10",
  "ui":true
}
[root@db-server-yayun-01 ~]#

consul client（192.168.0.20,192.168.0.30,192.168.0.40）

[root@db-server-yayun-02 ~]# cat /etc/consul.d/client.json 
{
  "data_dir": "/data/consul",
  "enable_script_checks": true,
  "bind_addr": "192.168.0.20",
  "retry_join": ["192.168.0.10"],
  "retry_interval": "30s",
  "rejoin_after_leave": true,
  "start_join": ["192.168.0.10"]
}
[root@db-server-yayun-02 ~]#

3台服务器的配置文件差异不大，唯一有区别的就是bind_addr地方，自行修改为你自己服务器的ip。我测试环境是虚拟机，有多快网卡，所以必须指定，否则可以绑定0.0.0.0。
下面我们先启动consul server：

nohup consul agent -config-dir=/etc/consul.d > /data/consul/consul.log &

查看日志：

[root@db-server-yayun-01 consul]# cat consul.log 
==> WARNING: BootstrapExpect Mode is specified as 1; this is the same as Bootstrap mode.
==> WARNING: Bootstrap mode enabled! Do not enable unless necessary
==> Starting Consul agent...
==> Consul agent running!
           Version: \'v0.9.2\'
           Node ID: \'5e612623-ec5b-386c-19be-d38876a9a46f\'
         Node name: \'db-server-yayun-01\'
        Datacenter: \'dc1\'
            Server: true (bootstrap: true)
       Client Addr: 192.168.0.10 (HTTP: 8500, HTTPS: -1, DNS: 8600)
      Cluster Addr: 192.168.0.10 (LAN: 8301, WAN: 8302)
    Gossip encrypt: false, RPC-TLS: false, TLS-Incoming: false

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

    2017/12/09 09:49:53 [INFO] raft: Initial configuration (index=1): [{Suffrage:Voter ID:192.168.0.10:8300 Address:192.168.0.10:8300}]
    2017/12/09 09:49:53 [INFO] raft: Node at 192.168.0.10:8300 [Follower] entering Follower state (Leader: "")
    2017/12/09 09:49:53 [INFO] serf: EventMemberJoin: db-server-yayun-01.dc1 192.168.0.10
    2017/12/09 09:49:53 [INFO] serf: EventMemberJoin: db-server-yayun-01 192.168.0.10
    2017/12/09 09:49:53 [INFO] agent: Started DNS server 192.168.0.10:8600 (udp)
    2017/12/09 09:49:53 [INFO] consul: Adding LAN server db-server-yayun-01 (Addr: tcp/192.168.0.10:8300) (DC: dc1)
    2017/12/09 09:49:53 [INFO] consul: Handled member-join event for server "db-server-yayun-01.dc1" in area "wan"
    2017/12/09 09:49:53 [INFO] agent: Started DNS server 192.168.0.10:8600 (tcp)
    2017/12/09 09:49:53 [INFO] agent: Started HTTP server on 192.168.0.10:8500
    2017/12/09 09:50:00 [ERR] agent: failed to sync remote state: No cluster leader
    2017/12/09 09:50:00 [WARN] raft: Heartbeat timeout from "" reached, starting election
    2017/12/09 09:50:00 [INFO] raft: Node at 192.168.0.10:8300 [Candidate] entering Candidate state in term 2
    2017/12/09 09:50:00 [INFO] raft: Election won. Tally: 1
    2017/12/09 09:50:00 [INFO] raft: Node at 192.168.0.10:8300 [Leader] entering Leader state
    2017/12/09 09:50:00 [INFO] consul: cluster leadership acquired
    2017/12/09 09:50:00 [INFO] consul: New leader elected: db-server-yayun-01
    2017/12/09 09:50:00 [INFO] consul: member \'db-server-yayun-01\' joined, marking health alive
    2017/12/09 09:50:03 [INFO] agent: Synced node info

可以从日志中看到(HTTP: 8500, HTTPS: -1, DNS: 8600)，http端口默认8500，在reload以及web ui会用到，dns端口是8600，在使用dns解析的时候会用到。还可以看到这台机器就是leader，consul: New leader elected: db-server-yayun-01。因为只有一台机器。所以生产环境一定要3个或者5个server。

下面启动3台client，3台client启动命令是一样的。然后查看其中一台client的日志：

nohup consul agent -config-dir=/etc/consul.d > /data/consul/consul.log &

[root@db-server-yayun-02 consul]# cat /data/consul/consul.log 
==> Starting Consul agent...
==> Joining cluster...
    Join completed. Synced with 1 initial agents
==> Consul agent running!
           Version: \'v0.9.2\'
           Node ID: \'0ec901ab-6c66-2461-95e6-50a77a28ed72\'
         Node name: \'db-server-yayun-02\'
        Datacenter: \'dc1\'
            Server: false (bootstrap: false)
       Client Addr: 127.0.0.1 (HTTP: 8500, HTTPS: -1, DNS: 8600)
      Cluster Addr: 192.168.0.20 (LAN: 8301, WAN: 8302)
    Gossip encrypt: false, RPC-TLS: false, TLS-Incoming: false

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

    2017/12/09 10:06:10 [INFO] serf: EventMemberJoin: db-server-yayun-02 192.168.0.20
    2017/12/09 10:06:10 [INFO] agent: Started DNS server 127.0.0.1:8600 (udp)
    2017/12/09 10:06:10 [INFO] agent: Started DNS server 127.0.0.1:8600 (tcp)
    2017/12/09 10:06:10 [INFO] agent: Started HTTP server on 127.0.0.1:8500
    2017/12/09 10:06:10 [INFO] agent: (LAN) joining: [192.168.0.10]
    2017/12/09 10:06:10 [INFO] agent: Retry join is supported for: aws azure gce softlayer
    2017/12/09 10:06:10 [INFO] agent: Joining cluster...
    2017/12/09 10:06:10 [INFO] agent: (LAN) joining: [192.168.0.10]
    2017/12/09 10:06:10 [INFO] serf: EventMemberJoin: db-server-yayun-01 192.168.0.10
    2017/12/09 10:06:10 [INFO] agent: (LAN) joined: 1 Err: <nil>
    2017/12/09 10:06:10 [INFO] consul: adding server db-server-yayun-01 (Addr: tcp/192.168.0.10:8300) (DC: dc1)
    2017/12/09 10:06:10 [INFO] agent: (LAN) joined: 1 Err: <nil>
    2017/12/09 10:06:10 [INFO] agent: Join completed. Synced with 1 initial agents
    2017/12/09 10:06:10 [INFO] agent: Synced node info

可以看到提示agent: Join completed. Synced with 1 initial agents，以及Server: false (bootstrap: false)。这也是client和server的区别。
我们继续执行命令看一下集群：

[root@db-server-yayun-02 ~]# consul members
Node                Address            Status  Type    Build  Protocol  DC
db-server-yayun-01  192.168.0.10:8301  alive   server  0.9.2  2         dc1
db-server-yayun-02  192.168.0.20:8301  alive   client  0.9.2  2         dc1
db-server-yayun-03  192.168.0.30:8301  alive   client  0.9.2  2         dc1
db-server-yayun-04  192.168.0.40:8301  alive   client  0.9.2  2         dc1
[root@db-server-yayun-02 ~]#

[root@db-server-yayun-02 ~]# consul operator raft list-peers
Node                ID                 Address            State   Voter  RaftProtocol
db-server-yayun-01  192.168.0.10:8300  192.168.0.10:8300  leader  true   2
[root@db-server-yayun-02 ~]#

我们看看web ui，consul自带的ui，非常轻便。访问：http://192.168.0.10:8500/ui/

到这来consul集群就搭建完成了，是不是很简单。对就是这么简单，但是从上面可以看到，client节点并没有注册服务，显示0 services。这也就是接下来需要讲解的。那么到底如何实现redis及mysql的高可用呢？正式开始：

Consul 使用场景一（redis sentinel）
(1)Redis 哨兵架构下,服务器部署了哨兵,但业务部门没有在app 层面,使用jedis 哨兵驱动来自动发现Redis master,而使用直连IP master。当master挂掉，其他redis节点担当新master后，应用需要手工修改配置，指向新master。
(2)Redis 客户端驱动,还没有读写分离的配置，若想slave的读负载均衡，暂时没好的办法。我们程序都是支持读写分离，所以没影响
(3)Consul 可以满足以上需求，配置两个DNS服务，一个是master的服务，利用consul自身的服务健康检查和探测功能，自动发现新的master。然后定义一个slave的服务，基于DNS本身，能够对slave角色的redis IP做轮询。

架构图如下：

同样也可以对mysql做高可用，mha和sentinel的角色一样，架构图如下：

下面就说说redis高可用的实现过程，mysql的我就不说了，mysql用到的健康检查脚本我会贴出来。思路都是一样的。

Consul 服务定义（Redis）

上面已经搭建好了consul集群，server是192.168.0.10 client是20到40. 那么20我们就拿来当redis master，30,40拿来当redis slave。下面定义服务（20,30,40都要存在）：

20,30,40的配置文件如下，除了address要修改为对应的服务器地址，其他一样。

[root@db-server-yayun-02 consul.d]# pwd
/etc/consul.d
[root@db-server-yayun-02 consul.d]# ll
total 12
-rw-r--r--. 1 root root 221 Dec  9 09:44 client.json
-rw-r--r--. 1 root root 319 Dec  9 10:48 r-6029-redis-test.json
-rw-r--r--. 1 root root 321 Dec  9 10:48 w-6029-redis-test.json
[root@db-server-yayun-02 consul.d]#

master的服务定义配置文件：

[root@db-server-yayun-02 consul.d]# cat w-6029-redis-test.json 
{
  "services": [
    {
      "name": "w-6029-redis-test",
      "tags": [
        "master-test-6029"
      ],
      "address": "192.168.0.20",
      "port": 6029,
      "checks": [
        {
          "script": "/data/consul/shell/check_redis_master.sh 6029 ",
          "interval": "15s"
        }
      ]
    }
  ]
}

[root@db-server-yayun-02 consul.d]#

slave的服务定义配置文件：

[root@db-server-yayun-02 consul.d]# cat r-6029-redis-test.json 
{
  "services": [
    {
      "name": "r-6029-redis-test",
      "tags": [
        "slave-test-6029"
      ],
      "address": "192.168.0.20",
      "port": 6029,
      "checks": [
        {
          "script": "/data/consul/shell/check_redis_slave.sh 6029 ",
          "interval": "15s"
        }
      ]
    }
  ]
}

[root@db-server-yayun-02 consul.d]#

每个agent都注册后，对应有两个域名:
w-6029-redis-test.service.consul （对应唯一一个master IP）
r-6029-redis-test.service.consul (对应两个slave IP，客户端请求时，随机分配一个）

其中"script": "/data/consul/shell/check_redis_slave.sh 6029 "代表对redis 6029端口进行健康检查，关于更多健康检查请查看官网介绍。

[root@db-server-yayun-03 shell]# pwd
/data/consul/shell
[root@db-server-yayun-03 shell]# ll
total 16
-rwxr-xr-x. 1 root root  480 Dec  9 10:56 check_mysql_master.sh
-rwxr-xr-x. 1 root root 3004 Dec  9 10:55 check_mysql_slave.sh
-rwxr-xr-x. 1 root root  254 Dec  9 10:51 check_redis_master.sh
-rwxr-xr-x. 1 root root  379 Dec  9 10:51 check_redis_slave.sh
[root@db-server-yayun-03 shell]#

/data/consul/shell目录下面有4个脚本，是对redis和mysql进行健康检查用的。脚本比较简单，大概就是如果只有一个master，那么读写都在master，如果有slave可用，那么读会在slave进行。如果slave复制不正常，或者复制延时，那么slave服务将不会注册。

[root@db-server-yayun-03 shell]# cat check_redis_master.sh 
#!/bin/bash
myport=$1
auth=$2
if [ ! -n "$auth" ]
then
auth=\'\\"\\"\'
fi
comm="/usr/local/bin/redis-cli -p $myport -a $auth "
role=`echo \'INFO Replication\'|$comm |grep -Ec \'role:master\'`
echo \'INFO Replication\'|$comm

if [ $role -ne 1 ]
then
    exit 2
fi

[root@db-server-yayun-03 shell]#

[root@db-server-yayun-03 shell]# cat check_redis_slave.sh 
#!/bin/bash
myport=$1
auth=$2
if [ ! -n "$auth" ]
then
auth=\'\\"\\"\'
fi
comm="/usr/local/bin/redis-cli -p $myport -a $auth "
role=`echo \'INFO Replication\'|$comm |grep -Ec \'^role:slave|^master_link_status:up\'`
single=`echo \'INFO Replication\'|$comm |grep -Ec \'^role:master|^connected_slaves:0\'`
echo \'INFO Replication\'|$comm

if [ $role -ne 2 -a $single -ne 2  ]
then
    exit 2
fi

[root@db-server-yayun-03 shell]#

[root@db-server-yayun-02 shell]# cat check_mysql_master.sh 
#!/bin/bash
port=$1
user="root"
passwod="123"

comm="/usr/local/mysql/bin/mysql -u$user -h 127.0.0.1 -P $port -p$passwod"
slave_info=`$comm -e "show slave status" |wc -l`
value=`$comm -Nse "select 1"`

# 判断是不是从库
if [ $slave_info -ne 0 ]
then
   echo "MySQL $port  Instance is Slave........"
   $comm -e "show slave status\\G" | egrep -w "Master_Host|Master_User|Master_Port|Master_Log_File|Read_Master_Log_Pos|Relay_Log_File|Relay_Log_Pos|Relay_Master_Log_File|Slave_IO_Running|Slave_SQL_Running|Exec_Master_Log_Pos|Relay_Log_Space|Seconds_Behind_Master"
   exit 2
fi


# 判断mysql是否存活
if [ -z $value ]
then
   exit 2
fi

echo "MySQL $port  Instance is Master........"
$comm -e "select * from information_schema.PROCESSLIST where user=\'repl\' and COMMAND like \'%Dump%\'"
[root@db-server-yayun-02 shell]#

[root@db-server-yayun-02 shell]# cat check_mysql_slave.sh 
#!/bin/bash
port=$1
user="root"
passwod="123"
repl_check_user="root"
repl_check_pwd="123"

master_comm="/usr/local/mysql/bin/mysql -u$user -h 127.0.0.1 -P $port -p$passwod"
slave_comm="/usr/local/mysql/bin/mysql -u$repl_check_user  -P $port -p$repl_check_pwd"

# 判断mysql是否存活
value=`$master_comm -Nse "select 1"`
if [ -z $value ]
then
   echo "MySQL Server is Down....."
   exit 2
fi

get_slave_count=0
is_slave_role=0
slave_mode_repl_delay=0
master_mode_repl_delay=0
master_mode_repl_dead=0
slave_mode_repl_status=0
max_delay=120

get_slave_hosts=`$master_comm -Nse "select substring_index(HOST,\':\',1) from information_schema.PROCESSLIST where user=\'repl\' and COMMAND like \'%Binlog Dump%\';" `
get_slave_count=`$master_comm -Nse "select count(1) from information_schema.PROCESSLIST where user=\'repl\' and COMMAND like \'%Binlog Dump%\';" `
is_slave_role=`$master_comm -e "show slave status\\G"|grep -Ewc "Slave_SQL_Running|Slave_IO_Running"`


### 单点模式(如果 get_slave_count=0 and is_slave_role=0)
function single_mode
{
if [ $get_slave_count -eq 0 -a $is_slave_role -eq 0 ]
then
    echo "MySQL $port  Instance is Single Master........"
    exit 0 
fi
}

### 从节点模式(如果 get_slave_count=0 and is_slave_role=2 ) 
function slave_mode
{
#如果是从节点,必须满足不延迟,
if [  $is_slave_role -ge 2 ]
then
        echo "MySQL $port  Instance is Slave........"
        $master_comm -e "show slave status\\G" | egrep -w "Master_Host|Master_User|Master_Port|Master_Log_File|Read_Master_Log_Pos|Relay_Log_File|Relay_Log_Pos|Relay_Master_Log_File|Slave_IO_Running|Slave_SQL_Running|Exec_Master_Log_Pos|Relay_Log_Space|Seconds_Behind_Master"
        slave_mode_repl_delay=`$master_comm -e "show slave status\\G" | grep -w "Seconds_Behind_Master" | awk \'{print $NF}\'`
        slave_mode_repl_status=`$master_comm -e "show slave status\\G"|grep -Ec "Slave_IO_Running: Yes|Slave_SQL_Running: Yes"`
if [ X"$slave_mode_repl_delay" == X"NULL" ]
then
        slave_mode_repl_delay=99999
fi
        if [ $slave_mode_repl_delay != "NULL" -a $slave_mode_repl_delay -lt $max_delay -a $slave_mode_repl_status -ge 2 ] 
        then
             exit 0
        fi
fi
} 

function master_mode
{
###如果是主节点，必须满足从节点为延迟或复制错误。才可读
if [ $get_slave_count -gt 0 -a $is_slave_role -eq  0 ]
then
    echo "MySQL $port  Instance is Master........"
    $master_comm -e "select * from information_schema.PROCESSLIST where user=\'repl\' and COMMAND like \'%Dump%\'"
    for my_slave in $get_slave_hosts
do 
master_mode_repl_delay=`$slave_comm -h $my_slave -e "show slave status\\G" | grep -w "Seconds_Behind_Master" | awk \'{print $NF}\' `
master_mode_repl_thread=`$slave_comm -h $my_slave -e "show slave status\\G"|grep -Ec "Slave_IO_Running: Yes|Slave_SQL_Running: Yes"`
if [ X"$master_mode_repl_delay" == X"NULL" ]
then
     master_mode_repl_delay=99999
fi

if [ $master_mode_repl_delay -lt $max_delay -a $master_mode_repl_thread -ge 2 ]
then
    exit 2
fi
done 
exit 0
fi
} 

single_mode
slave_mode
master_mode
exit 2
[root@db-server-yayun-02 shell]#

"name": "r-6029-redis-test",这个就是域名了，默认后缀是servers.consul，consul可以利用domain参数修改。配置文件生成以后安装redis，搭建主从复制（省略）。主从复制完成以后就可以重新reload consul了。redis info信息：

127.0.0.1:6029> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.0.40,port=6029,state=online,offset=6786,lag=0
slave1:ip=192.168.0.30,port=6029,state=online,offset=6786,lag=1
master_repl_offset:6786
repl_backlog_active:1
repl_backlog_size:67108864
repl_backlog_first_byte_offset:2
repl_backlog_histlen:6785
127.0.0.1:6029>

reload consul（3台client，也就是20-40）：

[root@db-server-yayun-02 ~]# consul reload
Configuration reload triggered
[root@db-server-yayun-02 ~]#

在其中一台服务器查看consul日志（20）：

[root@db-server-yayun-02 consul]# tail -f consul.log 
    2017/12/09 10:09:59 [INFO] serf: EventMemberJoin: db-server-yayun-04 192.168.0.40
    2017/12/09 11:14:55 [INFO] Caught signal:  hangup
    2017/12/09 11:14:55 [INFO] Reloading configuration...
    2017/12/09 11:14:55 [INFO] agent: Synced service \'r-6029-redis-test\'
    2017/12/09 11:14:55 [INFO] agent: Synced service \'w-6029-redis-test\'
    2017/12/09 11:14:55 [INFO] agent: Synced check \'service:w-6029-redis-test\'
    2017/12/09 11:15:00 [WARN] agent: Check \'service:r-6029-redis-test\' is now critical
    2017/12/09 11:15:15 [WARN] agent: Check \'service:r-6029-redis-test\' is now critical
    2017/12/09 11:15:30 [WARN] agent: Check \'service:r-6029-redis-test\' is now critical
    2017/12/09 11:15:45 [WARN] agent: Check \'service:r-6029-redis-test\' is now critical

可以看到r-6029-redis-test，w-6029-redis-test服务都已经注册，但是只有w-6029-redis-test注册成功，也就是写的，因为服务器20上面的redis是master，slave的服务当然无法注册成功。我们通过web ui看看。

可以看到3个client节点每个节点都已经注册了2个服务。还可以看到我们自定义的输出：

下面我们使用dns来解析看看，是否是我们想要的。我们注册两个服务。r-6029-redis-test，w-6029-redis-test，那么就是就产生了2个域名，分别是r-6029-redis-test.service.consul和w-6029-redis-test.service.consul。我们使用dig来看看：

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 r-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 r-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34508
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;r-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
r-6029-redis-test.service.consul. 0 IN  A       192.168.0.30
r-6029-redis-test.service.consul. 0 IN  A       192.168.0.40

;; Query time: 1 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:26:38 2017
;; MSG SIZE  rcvd: 82

[root@db-server-yayun-02 ~]#

我们可以看到读的域名r-6029-redis-test.service.consul解析到了两台服务器。那么我们就能够对从库进行负载均衡了。那么写的域名呢？

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 w-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 w-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7451
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;w-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
w-6029-redis-test.service.consul. 0 IN  A       192.168.0.20

;; Query time: 1 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:27:59 2017
;; MSG SIZE  rcvd: 66

[root@db-server-yayun-02 ~]#

和我们预料的没错，解析在了20上面。那么我们如果关闭其中一个从库会是怎样的？

[root@db-server-yayun-03 ~]# ifconfig eth1 | grep -oP \'(?<=inet addr:)\\S+\'         
192.168.0.30
[root@db-server-yayun-03 ~]# pgrep -fl redis-server | awk \'{print $1}\' | xargs kill
[root@db-server-yayun-03 ~]#

127.0.0.1:6029> info replication
# Replication
role:master
connected_slaves:1
slave0:ip=192.168.0.40,port=6029,state=online,offset=8200,lag=0
master_repl_offset:8200
repl_backlog_active:1
repl_backlog_size:67108864
repl_backlog_first_byte_offset:2
repl_backlog_histlen:8199
127.0.0.1:6029>

可以看到只有一个从了，我们再次dig 读域名看看：

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 r-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 r-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41984
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;r-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
r-6029-redis-test.service.consul. 0 IN  A       192.168.0.40

;; Query time: 8 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:32:46 2017
;; MSG SIZE  rcvd: 66

[root@db-server-yayun-02 ~]#

可以看到踢掉了另外一台机器。如果我再次关闭40这个从呢？

[root@db-server-yayun-04 shell]# ifconfig eth1 | grep -oP \'(?<=inet addr:)\\S+\' 
192.168.0.40
[root@db-server-yayun-04 shell]# pgrep -fl redis-server | awk \'{print $1}\' | xargs kill
[root@db-server-yayun-04 shell]#

那么我们的redis就没有可用从库了，那么读写都将在master上面。

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 r-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 r-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 58564
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;r-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
r-6029-redis-test.service.consul. 0 IN  A       192.168.0.20

;; Query time: 4 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:35:11 2017
;; MSG SIZE  rcvd: 66

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 w-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 w-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56965
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;w-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
w-6029-redis-test.service.consul. 0 IN  A       192.168.0.20

;; Query time: 5 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:35:16 2017
;; MSG SIZE  rcvd: 66

[root@db-server-yayun-02 ~]#

这里测试的就差不多了，下面结合sentinel来实现高可用。我会恢复刚才的环境。也就是20是master，30,40是slave。10是sentinel。生产环境sentinel也要部署3个或5个。我的10上面已经有sentinel，端口是36029，我直接添加对20的6029监控。

127.0.0.1:36029> sentinel monitor my-test-6029 192.168.0.20 6029 1
OK
127.0.0.1:36029>

127.0.0.1:36029> info Sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
master0:name=my-test-6029,status=ok,address=192.168.0.20:6029,slaves=2,sentinels=1
127.0.0.1:36029>

再次看看读写域名是否正常了，我已经恢复环境：

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 w-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 w-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62669
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;w-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
w-6029-redis-test.service.consul. 0 IN  A       192.168.0.20

;; Query time: 2 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:43:04 2017
;; MSG SIZE  rcvd: 66

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 r-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 r-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41305
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;r-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
r-6029-redis-test.service.consul. 0 IN  A       192.168.0.30
r-6029-redis-test.service.consul. 0 IN  A       192.168.0.40

;; Query time: 2 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:43:08 2017
;; MSG SIZE  rcvd: 82

[root@db-server-yayun-02 ~]#

可以看到已经正常，现在关闭redis master：

[root@db-server-yayun-02 ~]# ifconfig eth1 | grep -oP \'(?<=inet addr:)\\S+\'
192.168.0.20
[root@db-server-yayun-02 ~]# pgrep -fl redis-server | awk \'{print $1}\' | xargs kill

看看sentinel信息：

127.0.0.1:36029> info Sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
master0:name=my-test-6029,status=ok,address=192.168.0.30:6029,slaves=2,sentinels=1
127.0.0.1:36029>

可以看到master已经是30了，dig域名看看：

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 w-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 w-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55527
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;w-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
w-6029-redis-test.service.consul. 0 IN  A       192.168.0.30

;; Query time: 2 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:45:46 2017
;; MSG SIZE  rcvd: 66

[root@db-server-yayun-02 ~]# dig @192.168.0.10 -p 8600 r-6029-redis-test.service.consul

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @192.168.0.10 -p 8600 r-6029-redis-test.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11563
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;r-6029-redis-test.service.consul. IN   A

;; ANSWER SECTION:
r-6029-redis-test.service.consul. 0 IN  A       192.168.0.40

;; Query time: 1 msec
;; SERVER: 192.168.0.10#8600(192.168.0.10)
;; WHEN: Sat Dec  9 11:45:50 2017
;; MSG SIZE  rcvd: 66

[root@db-server-yayun-02 ~]#

ok，可以看到已经是我们想要的结果了。最后说说dns的问题。

App端配置域名服务器IP来解析consul后缀的域名，DNS解析及跳转，有三个方案：
1. 原内网dns服务器,做域名转发，consul后缀的，都转到consul server上（我们线上是采用这个）
2. dns全部跳到consul DNS服务器上，非consul后缀的,使用 recursors 属性跳转到原DNS服务器上
3. dnsmaq 转： server=/consul/10.16.X.X#8600 解析consul后缀的

我们内网dns是用的bind，对于bind的如何做域名转发consul官网也有栗子：https://www.consul.io/docs/guides/forwarding.html，另外也对consul的dns进行了压力测试，不存在性能问题：