#mysql_role_swap

mysql_roles_swap is a script written in Ruby to perform all of the tasks that we normally perform when promoting a slave database to master. It performs all of the necessary checks to be sure that the transition is as smooth as possible. It uses the mysql and activerecord libraries to perform these tasks.

mysql_role_swap is based on a few key design concepts: The script should be easy to understand and trouble shoot. The script should handle errors gracefully and provide ample data for manual recovery in the event human intervention is needed. We should be deterministic about the state of each step of the failover process.

In April 2011, after planning yet another manual database failover, Taylor shared the use of a statemachine and original design concept with John. One weekend later version one was born and reliably working on some test virtual machines. Since April 2011 John has shepherded the script through multiple rounds of testing in a staging environment. Taylor got the bright idea to add support for moving a virtual IP to the script, and since then the script has been used numerous times in production database environments without issue.

We've designed myslq_role_swap to do work reliably in our environment at 37signals however we believe through wider adoption and contributions from other organizations this script can become even more efficient and reliable. Almost all of the configuration is done by our Chef recipes -- and thus things are a little environment specific right now. With your help we can make this a little less 37-specific.

How do I use it?

The script has been deployed on all of our database servers. And it is located at:

/usr/local/bin/mysql_role_swap

When running the script you must specify at least one of the following options:

• Database Instance Name (-d): The name of the MySQL instance that you are swapping roles on. (This is used create the path to the cluster.yml file)
• Full Config Path (-c): Full path to the cluster.yml file.

Optional options:

• Check (-s): The check option will only run the preflight checks on the database and will not attempt to fail over.
• Force (-f): The force option will not prompt you before failing over the database. If there is a configuration problem the failover will not proceed. (use carefully)

You also need a cluster.yml file so the script can do all it's magic correctly.

Here's a sample cluster.yml:

floating_ip: 10.10.10.37
floating_ip_cidr: /32
master_ipmi_address: 10.10.99.137

database_one:
  adapter: mysql
  username: failover_user
  password: iluvsql
  primary_database: 37_production
  host: 10.10.9.137
  port: 3306
  slave_password: iluvsql2

database_two:
  adapter: mysql
  username: failover_user
  password: iluvsql
  primary_database: 37_production
  host: 10.10.9.138
  port: 3306
  slave_password: iluvsql2

Example Usage:

Using the "-d" option:

mysql_role_swap -d failovertest
Current Cluster Configuration:

Floating IP: 10.10.3.160

Master: dbslave:3310
MySQL Replication Role: master
Floating IP Role: master
MySQL Version: [5.1.45-log]
Read-Only: false
Arping Path: /usr/bin/arping

Slave: shr-db-02:3307
MySQL Replication Role: slave
Floating IP Role: slave
MySQL Version: [5.1.45-log]
Read-Only: true
Arping Path: /usr/bin/arpingon:[5.1.45-log] Read-Only: true

The fastest way to get help is to send an email to [email protected]. Github issues and pull requests are checked regularly.

Pull requests with passing tests are welcomed and appreciated.

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