README.md

PG Streaming Replication - Docker

This project is for understanding how can I quickly bootstrap a master-replica postgresql db environment with streaming replication enabled.

Run Instructions

1. To start master and replica containers (with streaming replication enabled):

   docker-compose up

2. To stop the running containers

   docker-compose down

3. To get inside any container, first run

   docker ps

   to get the container name/id, then run

   docker exec -it <name or id of container> /bin/bash

   Inside the container run

   su - postgres

   to change to user postgres, and psql can be connected to as:

   psql -U surbhit -d testdb

Note: ssh, less, vim installation on any container is actually not needed. It is for a personal project.

Play Around

Replication Check

Insert the following data into master

Connect to the master db

docker exec -it pg_streaming_replication_pg_master_1 /bin/bash
su - postgres
psql -U surbhit -d testdb

and run the following commands to insert data into db.

CREATE TABLE persons (
id INTEGER PRIMARY KEY,
name VARCHAR (10)
);

INSERT INTO persons
VALUES (1, 'alice');

INSERT INTO persons
VALUES (2, 'bob');

INSERT INTO persons
VALUES (3, 'claire');

Connect to the replica db

docker exec -it pg_streaming_replication_pg_replica_1 /bin/bash
su - postgres
psql -U surbhit -d testdb

and run the following command to see that data is replicated:

SELECT * FROM persons;

Failover of Master Node

To simulate a failure of master run:

docker stop pg_streaming_replication_pg_master_1

After this you can see that the replica logs start complaining in the docker-compose up terminal (which streams logs from master and replica container)

To promote the replica to master, on the replica container run

touch /tmp/pg_ctl_promote

In the docker-compose up terminal you will see that now replica can accept both read and write connections.

Note: Once replica is promoted to master if (original) master is brought back up, we have 2 db server and two db instances.