Learning Docker http://docker.io/ by creating a pgpool cluster

####Requirements

• docker that supports exec command ('exec' is available starting from docker version 1.3)

###Pgpool2 cluster + Postgresql Streaming Replication Test To understand setup architecture, please take a look at:

• http://www.pgpool.net/pgpool-web/contrib_docs/watchdog/en.html
• http://www.pgpool.net/docs/pgpool-II-3.2.0/wd-en.html
• https://github.com/faja/howtos/blob/master/sql/postgresql/README.md

This simple scripts will help you to learn more about docker and pgpool clustering.

####Initial setup

1. To create environment run script pgpool.sh. It will launch 6 docker containers and prepare all the config files:

• the application (app) [you can deploy any app in this container to access pgpool cluster]
• master (postgresql)
• slave1 (postgresql)
• slave2 (postgresql)
• pgpool-1 (pgpool2 node)
• pgpool-2 (pgpool2 node)

If everything goes smoothhly, you will see similar message in the end:

* Starting pgpool-II pgpool
   ...done.
3
master 5432 1 0.000000
slave1 5432 1 0.500000
slave2 5432 3 0.500000

Later if you need to get information about pgpool status and its nodes roles, just run:

./sh_pool_nodes.sh

 node_id | hostname | port | status | lb_weight |  role
---------+----------+------+--------+-----------+---------
 0       | master   | 5432 | 3      | 0.000000  | primary
 1       | slave1   | 5432 | 2      | 0.500000  | standby
 2       | slave2   | 5432 | 2      | 0.500000  | standby
(3 rows)

This means that pool is up and functioning, and all the servers in pool are online. You can run docker ps and check what containers have been created:

CONTAINER ID        IMAGE                      COMMAND             CREATED             STATUS              PORTS                       NAMES
1014dee46ebc        postmart/psql-9.3:latest   "/bin/bash"         2 hours ago         Up 2 hours                                      pgpool-1
ba2edb256668        postmart/psql-9.3:latest   "/bin/bash"         2 hours ago         Up 2 hours                                      pgpool-2
ec397860af5a        postmart/psql-9.3:latest   "/bin/bash"         2 hours ago         Up 2 hours                                      app
3d5ad6d50d8f        postmart/psql-9.3:latest   "/bin/bash"         2 hours ago         Up 2 hours                                      slave2
c2fc3b670868        postmart/psql-9.3:latest   "/bin/bash"         2 hours ago         Up 2 hours                                      slave1
13cbdbc1d698        postmart/psql-9.3:latest   "/bin/bash"         2 hours ago         Up 2 hours                                      master

So we have 2 pgpool nodes to avoid SPOF. This means that our application container will access database using virtual IP. Check delegate_ip file to see default virtual IP. Change this IP to any you want.

Tests:

./test.sh : # simulate failure of master db server and automatic failover
./test_recover_master.sh : # recover initial master in case it went down
./find_lags.sh # calculating streaming replication lags in seconds

Dockerfile

There is ruby installed in the docker image, as I am locally testing with rails app. Feel free to remove ruby from the image to free some space.