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Governor: A Template for PostgreSQL HA with etcd

Docker based Postgres Cluster: Streaming Replication with automatic setup out of the box, batteries included.

Automatic Failover. Zero Downtime Upgrades. Configurable via ENV variables, with etcd cluster for master election as external service. Production ready, stable, and fully dev-ops approved.

This is a fork of https://github.com/compose/governor with a few improvements to make it cluster safe and production ready.

USAGE

Set up three docker hosts,

  • server1: 192.168.42.1
  • server2: 192.168.42.2
  • server3: 192.168.42.3

Let's run a single etcd node for now:

docker -H tcp://server1:2375 run -d --name etcd1 --net host coreos/etcd -addr 192.168.42.1:4001 -peer-addr 192.168.42.1:4002

Now let's run up three governor nodes:

docker -H tcp://server1:2375 run -d --name pg1 --net host \
  -e GOVERNOR_ETCD_HOST=192.168.42.1:4001 \
  -e GOVERNOR_POSTGRESQL_NAME=postgresql1 \
  -e GOVERNOR_POSTGRESQL_LISTEN=192.168.42.1:5432 \
  -e GOVERNOR_POSTGRESQL_DATA_DIR=/data/postgres \
  -e GOVERNOR_POSTGRESQL_REPLICATION_NETWORK=192.168.42.1/24 miketonks/governor

  docker -H tcp://server2:2375 run -d --name pg2 --net host \
    -e GOVERNOR_ETCD_HOST=192.168.42.1:4001 \
    -e GOVERNOR_POSTGRESQL_NAME=postgresql2 \
    -e GOVERNOR_POSTGRESQL_LISTEN=192.168.42.2:5432 \
    -e GOVERNOR_POSTGRESQL_DATA_DIR=/data/postgres \
    -e GOVERNOR_POSTGRESQL_REPLICATION_NETWORK=192.168.42.1/24 miketonks/governor

    docker -H tcp://server3:2375 run -d --name pg3 --net host \
      -e GOVERNOR_ETCD_HOST=192.168.42.1:4001 \
      -e GOVERNOR_POSTGRESQL_NAME=postgresql3 \
      -e GOVERNOR_POSTGRESQL_LISTEN=192.168.42.3:5432 \
      -e GOVERNOR_POSTGRESQL_DATA_DIR=/data/postgres \
      -e GOVERNOR_POSTGRESQL_REPLICATION_NETWORK=192.168.42.1/24 miketonks/governor

The first node started will assume master role, and the other two will become slaves.

$docker logs pg1

2015-07-10 16:10:32,404 INFO: Governor Starting up: Starting Postgres
2015-07-10 16:10:34,460 INFO: Governor Running: Starting Running Loop
2015-07-10 16:10:39,474 INFO: Lock owner: postgresql1; I am postgresql1
2015-07-10 16:10:39,476 INFO: Governor Running: no action.  i am the leader with the lock
2015-07-10 16:10:39,476 INFO: Governor Running: I am the Leader
2015-07-10 16:10:39,477 INFO: Governor Running: Create Replication Slot: postgresql2
2015-07-10 16:10:49,495 INFO: Lock owner: postgresql1; I am postgresql1
2015-07-10 16:10:49,497 INFO: Governor Running: no action.  i am the leader with the lock
2015-07-10 16:10:49,497 INFO: Governor Running: I am the Leader

$docker logs pg2

2015-07-10 16:10:32,404 INFO: Governor Starting up: Starting Postgres
2015-07-10 16:10:32,416 INFO: Governor Running: Starting Running Loop
FATAL:  the database system is starting up
LOG:  started streaming WAL from primary at 0/3000000 on timeline 1
LOG:  redo starts at 0/3000028
LOG:  consistent recovery state reached at 0/30000F0
LOG:  database system is ready to accept read only connections
2015-07-10 16:10:52,461 INFO: Lock owner: postgresql1; I am postgresql2
2015-07-10 16:10:52,461 INFO: does not have lock
2015-07-10 16:10:52,465 INFO: Governor Running: no action.  i am a secondary and i am following a leader

Now kill the pg1 node and you will see, after a short while, that pg2 (or pg3) automatically reconfigures and takes over as primary

Bring pg1 back online and it will rejoin the cluster as a slave.