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Amplify::Failover

Overview

Architecture Diagram

Running it

To build

./build.sh

To run

./go

To specify the config file

FAILOVER_CONFIG=config/myconfig.yaml ./go

To specify the server port

FAILOVER_CONFIG=config/myconfig.yaml ./go server[8888]

Privileges Required

MySQL Watchdog

The MySQL watchdog MySQL user requires the following privileges

  • SUPER on *.* to set read_only on and off, stop/start slaves
  • PROCESS on *.* to kill attached connections
  • ALL PRIVILEGES on the failover database in order to create and read/write to the tracking table

The system user only needs privileges to read the config file and bind to the specified port.

Application Watchdog

The system user requires the following permissions and privileges

  • read the config file and bind to the specified port
  • execute the commands specified in application.cmd_on_* in the config file. This probably means limited sudo access in order to restart the service.

How to Fail Over A Database

Any of these commands may be executed by SSHing into any node within an environment and application that is running the failover watchdog. For example, mysql-001, mysql-002, web-001, web-002 all run the failover watchdog for the named application.

To list available fail over targets

$ sudo java -jar /opt/failover/failover.war -S bin/failover -c /etc/failover/failover.yaml list
Available fail over targets (* denotes currently active master):
* mysql-001
  mysql-002

To fail over to a new database

$ sudo java -jar /opt/failover/failover.war -S bin/failover -c /etc/failover/failover.yaml failover mysql-002
I, [2014-03-12T17:39:12.662000 #1969]  INFO -- : Failing over to mysql-002...
I, [2014-03-12T17:39:13.050000 #1969]  INFO -- : /failover_state changed.  New value: transitioning
I, [2014-03-12T17:39:13.054000 #1969]  INFO -- : State changed to transitioning
I, [2014-03-12T17:39:13.055000 #1969]  INFO -- : Failover in progress...
I, [2014-03-12T17:39:13.115000 #1969]  INFO -- : /failover_state changed.  New value: complete
I, [2014-03-12T17:39:13.116000 #1969]  INFO -- : State changed to complete
I, [2014-03-12T17:39:13.122000 #1969]  INFO -- : Failover complete.

Failing over to a new database can take at least 60 seconds, depending on the value of mysql.tracking_max_wait_secs in failover.yml. If it takes more than 2x tracking_max_wait_secs, something might be stuck and you should look at the logs on other hosts.