MySQL Router 是 InnoDB Cluster 架构的访问入口，在架构部署上，官方给出的建议是 router 与应用端绑定部署，避免 router 单点问题。
之前还有客户咨询，能否 router 不与应用端绑定部署，不便于部署，在此之前都需要在 router 前面加 VIP 或者一层负载均衡。
我还在想这事儿就应该由 MySQL Connector 来实现访问链路的 Failover 和 Loadbalance， 现在有了 DNS SRV 的支持，router 不必和应用端绑定部署，也可以省了 VIP 和负载均衡，MySQL InnoDB Cluster 方案更加完善，配合 consul 等服务发现组件，更容易适配 service mesh 架构。
DNS SRV 是 DNS 记录的一种，用来指定服务地址。SRV 记录不仅有服务目标地址，还有服务的端口，并且可以设置每个服务地址的优先级和权重。
Connector/NET
Connector/ODBC
Connector/J
Connector/Node.js
Connector/Python
Connector/C++
我们来演示下应用是如何使用 DNS SRV 的，这里使用 consul 做服务发现。
我在本机做了测试。
for i in `seq 4000 4002`; do
echo "Deploy mysql sandbox $i"
mysqlsh -- dba deploy-sandbox-instance $i --password=root
done
echo "Create innodb cluster..."
mysqlsh root@localhost:4000 -- dba create-cluster cluster01
mysqlsh root@localhost:4000 -- cluster add-instance --recoveryMethod=clone --password=root root@localhost:4001
mysqlsh root@localhost:4000 -- cluster add-instance --recoveryMethod=clone --password=root root@localhost:4002
for i in 6446 6556; do
echo "Bootstrap router $i"
mysqlrouter --bootstrap root@localhost:4000 --conf-use-gr-notifications -d router_$i --conf-base-port $i --name router_$i
sed -i 's/level = INFO/level = DEBUG/g router_$i/mysqlrouter.conf
sh router_$i/stop.sh
sh router_$i/start.sh
done
echo "Install consul..."
brew install consul
consul agent -dev &
echo "Services register..."
consul services register -name router -id router1 -port 6446 -tag rw
consul services register -name router -id router2 -port 6556 -tag rw
echo "Test dns srv..."
dig router.service.consul SRV -p 8600
;; QUESTION SECTION:
;router.service.consul. IN SRV
;; ANSWER SECTION:
router.service.consul. 0 IN SRV 1 1 6556 MBP.node.dc1.consul.
router.service.consul. 0 IN SRV 1 1 6446 MBP.node.dc1.consul.
;; ADDITIONAL SECTION:
MBP.node.dc1.consul. 0 IN A 127.0.0.1
MBP.node.dc1.consul. 0 IN TXT "consul-network-segment="
MBP.node.dc1.consul. 0 IN A 127.0.0.1
MBP.node.dc1.consul. 0 IN TXT "consul-network-segment="
echo "Install dnsmasq..."
brew install dnsmasq
echo 'server=/consul/127.0.0.1#8600' > /usr/local/etc/dnsmasq.d/consul
sudo brew services restart dnsmasq
echo "Test dns forwarding..."
dig router.service.consul SRV
pip install mysql-connector-python
import mysql.connector
cnx = mysql.connector.connect(user='root', password='root', database='mysql_innodb_cluster_metadata', host='router.service.consul', dns_srv=True)
cursor = cnx.cursor()
query = ("select instance_id from v2_this_instance")
cursor.execute(query)
for (instance_id) in cursor:
print("instance id: {}".format(instance_id))
cursor.close()
cnx.close()
从 MySQL Router 日志中可以看到请求以负载均衡方式发送到两边。
