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架构特性：
1，高可用
2，读写分离，查询路由
3，sql过滤等功能

Installation of Consul:
Firstly, we’ll need to install the required packages, download the Consul archive and perform the initial configuration. We’ll need to perform the same installation on each of the nodes (i.e., appserver, mysql1 and mysql2).
Install pre-requisite packages:
sudo yum -y install wget unzip bind-utils dnsmasq
Install Consul:
sudo useradd consul
sudo mkdir -p /opt/consul /etc/consul.d
sudo touch /var/log/consul.log /etc/consul.d/proxysql.json
cd /opt/consul
sudo wget https://releases.hashicorp.com/consul/0.6.4/consul_0.6.4_linux_amd64.zip
sudo unzip consul_0.6.4_linux_amd64.zip
sudo ln -s /opt/consul/consul /usr/bin/consul
sudo chown consul:consul -R /etc/consul /opt/consul /var/log/consul.log

Configuration of Consul on Application Server (used as ‘bootstrap’ node):
Now, that we’re done with the installation on each of the hosts, let’s continue with the configuration. In this example we’ll bootstrap the Consul cluster using “appserver”:

Edit configuration files
$ sudo vi /etc/consul.conf
{
"datacenter": "dc1",
"data_dir": "/opt/consul/",
"log_level": "INFO",
"node_name": "agent1",
"server": true,
"ui": true,
"bootstrap": true,
"client_addr": "0.0.0.0",
"advertise_addr": "192.168.1.119"  ## Add server IP here
}
######
$ sudo vi /etc/consul.d/proxysql.json
{"services": [
{
"id": "proxy1",
"name": "proxysql",
"address": "192.168.1.120",
"tags": ["mysql"],
"port": 6033,
"check": {
"script": "mysqladmin ping --host=192.168.1.120 --port=6033 --user=root --password=123",
"interval": "3s"}
},
{
"id": "proxy2",
"name": "proxysql",
"address": "192.168.1.121",
"tags": ["mysql"],
"port": 6033,
"check": {
"script": "mysqladmin ping --host=192.168.1.121 --port=6033 --user=root --password=123",
"interval": "3s"}
}
]
}

Start Consul agent
$ sudo su - consul -c 'consul agent -config-file=/etc/consul.conf -config-dir=/etc/consul.d > /var/log/consul.log &'

Setup DNSMASQ (as root)
vim /etc/dnsmasq.conf
resolv-file=/etc/resolv.conf
server=/consul/127.0.0.1#8600
service dnsmasq restart

Remember to add the localhost as a DNS server (this step can vary
depending on how your DNS servers are managed... here I'm just
adding the following line to resolve.conf:
sudo vi /etc/resolve.conf
#... snippet ...#
nameserver 127.0.0.1
#... snippet ...#
Restart dnsmasq
sudo service dnsmasq restart

====================================================================

Configuration of Consul on Proxy Servers:
The next item is to configure each of the proxy Consul agents. Note that the “agent name” and the “IP address” need to be updated for each host (values for both must be unique):

Edit configuration files
$ sudo vi /etc/consul.conf
{
"datacenter": "dc1",
"data_dir": "/opt/consul/",
"log_level": "INFO",
"node_name": "agent2",  ### Agent node name must be unique
"server": true,
"ui": true,
"bootstrap": false,   ### Disable bootstrap on joiner nodes
"client_addr": "0.0.0.0",
"advertise_addr": "192.168.1.xxx",  ### Set to local instance IP
"dns_config": {
"only_passing": true
}
}
######
$ sudo vi /etc/consul.d/proxysql.json
{"services": [
{
"id": "proxy1",
"name": "proxysql",
"address": "192.168.1.120",
"tags": ["mysql"],
"port": 6033,
"check": {
"script": "sh /etc/consul.d/test.sh",
"interval": "3s"}
},
{
"id": "proxy2",
"name": "proxysql",
"address": "192.168.1.121",
"tags": ["mysql"],
"port": 6033,
"check": {
"script": "sh /etc/consul.d/test.sh",
"interval": "3s"}
}
]
}

=============================================================

[root@localhost consul.d]# more test.sh
mysql -u haproxy -h 127.0.0.1 -P 3306 -e "select 1" >/dev/null 2>&1

if [ "$?" -ne 0 ]
then echo "not available"
exit 8
fi

==============================================================

Start Consul agent:
$ sudo su - consul -c 'consul agent -config-file=/etc/consul.conf -config-dir=/etc/consul.d > /var/log/consul.log &'
Join Consul cluster specifying 1st node IP e.g.
$ consul join 192.168.1.119
Verify logs and look out for the following messages:
$ cat /var/log/consul.log
==> Starting Consul agent...
==> Starting Consul agent RPC...
==> Consul agent running!
Node name: 'agent2'
Datacenter: 'dc1'
Server: true (bootstrap: false)
Client Addr: 0.0.0.0 (HTTP: 8500, HTTPS: -1, DNS: 8600, RPC: 8400)
Cluster Addr: 192.168.1.120 (LAN: 8301, WAN: 8302)
Gossip encrypt: false, RPC-TLS: false, TLS-Incoming: false
Atlas:
==> Log data will now stream in as it occurs:
... snippet ...
2016/09/05 19:48:04 [INFO] agent: Synced service 'consul'
2016/09/05 19:48:04 [INFO] agent: Synced check 'service:proxysql1'
2016/09/05 19:48:04 [INFO] agent: Synced check 'service:proxysql2'
... snippet ...

=============================================================================

Install ProxySQL packages and initialise ProxySQL DB
sudo yum -y install https://github.com/sysown/proxysql/releases/proxysql-1.4.3-1-centos67.x86_64.rpm
sudo service proxysql initial
sudo service proxysql stop
Edit the ProxySQL configuration file to update username / password
vi /etc/proxysql.cnf

admin_variables=
{
admin_credentials="admin:admin"
mysql_ifaces="127.0.0.1:6032;/tmp/proxysql_admin.sock"
}

Start ProxySQL
sudo service proxysql start
Connect to ProxySQL and configure
mysql -P6032 -h227.0.0.1 -uadmin -padmin
First we create a replication hostgroup:
mysql> INSERT INTO mysql_replication_hostgroups VALUES (10,11,'Standard Replication Groups');
Add both nodes to the hostgroup 11 (ProxySQL will automatically put the writer node in hostgroup 10)
mysql> INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.120',10,3306,1000);
mysql> INSERT INTO mysql_servers (hostname,hostgroup_id,port,weight) VALUES ('192.168.1.121',11,3306,1000);
Save server configuration
mysql> LOAD MYSQL SERVERS TO RUNTIME; SAVE MYSQL SERVERS TO DISK;
Add query rules for RW split
mysql> INSERT INTO mysql_query_rules (active, match_pattern, destination_hostgroup, cache_ttl, apply) VALUES (1, '^SELECT . FOR UPDATE', 10, NULL, 1);
mysql> INSERT INTO mysql_query_rules (active, match_pattern, destination_hostgroup, cache_ttl, apply) VALUES (1, '^SELECT .', 11, NULL, 1);
mysql> LOAD MYSQL QUERY RULES TO RUNTIME; SAVE MYSQL QUERY RULES TO DISK;
Finally configure ProxySQL user and save configuration
mysql> INSERT INTO mysql_users (username,password,active,default_hostgroup,default_schema) VALUES ('root','123',1,10,'test');
mysql> LOAD MYSQL USERS TO RUNTIME; SAVE MYSQL USERS TO DISK;
mysql> EXIT;

总结，坑点：
1，用户访问的数据库，主从，读写都是通过hostgroup 要定义和标识，所以这个参数一定对应

2，consul 健康检查
如果健康script 脚本返回error code 为1 ，code 1 只是warning ,还是会被解析，所以修改检查脚本内容，如果不匹配，手动返回error code 2或者其他值,之后这个异常服务才不解析。

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