dosemeau/pgcluster-postgres repository overview

⁠Streaming replication cluster for pgsql + pgpool2

This project⁠ includes dockerfiles for building a postgresql cluster and example of docker-compose⁠ file to start this cluster. It is based on https://github.com/paunin/postgres-docker-cluster⁠.

It varies from the version by not adding users to pg_hba.conf, and not exposing ports automatically. It has been designed to be deployed into an environment where a load balancer or proxy will handle this for you.

Two docker images can be produced:

• Postgresql server image which can start in master or slave mode: https://hub.docker.com/r/dosemeau/pgcluster-postgresql/⁠
• Pgpool service with flexible configurations: https://hub.docker.com/r/dosemeau/pgcluster-pgpool/⁠

⁠Schema of cluster

pgmaster (primary node1)  --|
|- pgslave1 (node2)       --|
|  |- pgslave2 (node3)    --|----pgpool (master_slave_mode stream)
|- pgslave3 (node4)       --|
   |- pgslave4 (node5)    --|

Each postgres node (pgmaster, pgslaveX) is managed by repmgr/repmgrd. It allows to use automatic failover. Depending on the environment settings, they will either stream off pgmaster or another slave.

To start a cluster, run it as a normal docker-compose application docker-compose up

Please check comments for each ENV variable in docker-compose⁠ file to understand the related parameter of cluster's node

⁠Useful commands

• Get map of current cluster(in any node): gosu postgres repmgr cluster show

⁠Scenarios

⁠Changing primary/master server on crash

Kill master container and in a few moments cluster will define new master node, and Pgpool will try to detect new primary node for write access automatically.

⁠Known problems

• Killing of node in the middle (e.g. pgslave1) will cause nodes that stream off it to die as well. (https://groups.google.com/forum/?hl=fil#!topic/repmgr/lPAYlawhL0o⁠)

⁠FAQ

• How to promote master, after failover on postgresql with docker⁠

⁠Documentation and manuals

• Original project: https://github.com/paunin/postgres-docker-cluster⁠
• Streaming replication in postgres: https://wiki.postgresql.org/wiki/Streaming_Replication⁠
• Repmgr: https://github.com/2ndQuadrant/repmgr⁠
• Pgpool2: http://www.pgpool.net/docs/latest/pgpool-en.html⁠