MySQL Role Checker

Checks if a node is master or slave, returning HTTP 200 if all is good.

Why ?

• Not going to use Galera yet
• Mysql-MHA is great, but corosync/pacemaker across DCs is not a good idea
• Running a local/centralized HAProxy doesn't hurt (search for airbnb's synapse/nerve combo)

Installation

go get github.com/lxfontes/myrolah

$ myrolah  -h
Usage of myrolah:
-lag=30: Slave Lag
-master=":7555": Master HTTP Check Port
-slave=":7556": Slave HTTP Check Port
-url="root:@tcp(127.0.0.1:3306)/information_schema": DB URL

Checks

Am I the master ?

A node will be classified as master if:

• MySQL is up
• It doesn't have any slave config (blank show slave status)
• Global read_only = OFF

Am I a slave ?

• MySQL is up
• Global read_only = ON
• Slave configuration is present (non-empty show slave status)
• Slave IO Thread is running
• Slave SQL Thread is running
• Slave is not lagging behind Master by X seconds

HAProxy

The trick is to setup a different port for healthchecks via check port

server db1 10.0.0.1:3306 check port 7556 inter 5s rise 2 fall 2 downinter 2s fastinter 1s

Check the sample haproxy.conf for a full example.

Flipping master / slave

Make sure to kill all connections on old-master when promoting a slave to master or you will get a lot of 'database is read-only errors'.