mysql_role_swap

mysql_role_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.

Design Concepts:

mysql_role_swap is based on a few key design concepts: The script should be easy to understand and troubleshoot. 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.

History:

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.

Improvements:

We've designed mysql_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.

Getting started

Installation

Pre-requisites

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 to 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 its 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/arping

Getting help and contributing

Getting help with mysql_role_swap

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

Contributing

Pull requests with passing tests are welcomed and appreciated.

License

 Copyright (c) 2012 37signals (37signals.com)

 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
 "Software"), to deal in the Software without restriction, including
 without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Software, and to
 permit persons to whom the Software is furnished to do so, subject to
 the following conditions:

 The above copyright notice and this permission notice shall be
 included in all copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.