Docker PostgreSQL How-To

Docker is one of the most exciting open source project right now. In short, it allows to easily create lightweight, portable, self-sufficient containers that can run any application, e.g. PostgreSQL service.

Back in June I created a Docker image for PostgreSQL service which became pretty popular on Docker Index. In this article, I'll show how to use this image and how I built it.

PostgreSQL service Prêt-à-Porter

The image I create allows you to easily launch with a running instance of PostgreSQL. It's no longer necessary to go through the usual pain of installing PostgreSQL server locally. Docker nicely encapsulates the whole process. Below is a slightly more verbose version of this gist.

Note: As of version 0.5.2, docker requires root privileges to run. You have to either manually adjust your system configuration (permissions on /var/run/docker.sock or sudo config), or prefix docker with sudo. Check this thread for details.

Fetch the image from Docker Index.

docker pull zaiste/postgresql

Run it, whether as a daemon or with the container output attached to your terminal screen.

CONTAINER=$(docker run -d zaiste/postgresql)

Identify which IP address has been assigned to this container

CONTAINER_IP=$(docker inspect $CONTAINER | grep IPAddress | awk '{ print $2 }' | tr -d ',"')

Finally, connect to PostgreSQL service (running on Docker) with psql.

psql -h $CONTAINER_IP -p 5432 -d docker -U docker -W

Note: psql must be installed locally.

Now it's all set up and ready. You can create roles and databases using psql.

psql (9.2.4)
Type "help" for help.

docker=# CREATE DATABASE foo OWNER=docker;
CREATE DATABASE

Enjoy.

Installing PostgreSQL on Docker

Let's now go through the process of creating a Docker image that provides a PostgreSQL service. For clarity I won't be showing commands output.

Run an interactive shell in Docker container.

docker run -i -t ubuntu /bin/bash

Update its dependencies.

apt-get update

Install python-software-properies.

apt-get install python-software-properties
apt-get install software-properties-common

Add Pitti's PostgreSQL repository. It contains the most recent stable release of PostgreSQL i.e. 9.2.

add-apt-repository ppa:pitti/postgresql
apt-get update

Finally, install PostgreSQL 9.2

apt-get -y install postgresql-9.2 postgresql-client-9.2 postgresql-contrib-9.2

Now, create a PostgreSQL superuser role that can create databases and other roles. Following Vagrant's convention the role will be named docker with docker password assigned to it.

sudo -u postgres createuser -P -d -r -s docker

Create a test database also named docker owned by previously created docker role.

sudo -u postgres createdb -O docker docker

Adjust PostgreSQL configuration so that remote connections to the database are possible. Make sure that inside /etc/postgresql/9.2/main/pg_hba.conf you have following line:

host    all             all             0.0.0.0/0               md5

Additionaly, inside /etc/postgresql/9.2/main/postgresql.conf uncomment listen_address so it is as follows:

listen_address='*'

Note: this PostgreSQL setup is for development only purposes. Refer to PostgreSQL documentation how to fine-tune these settings so that it is enough secure.

Exit the container, create an image and assign it a name. <container_id> is in the Bash prompt; you can also locate it using docker ps -a.

docker commit <container_id> <your username>/postgresql

Finally, run PostgreSQL server via docker.

CONTAINER=$(docker run -d -p 5432 \
  -t <your username>/postgresql \
  /bin/su postgres -c '/usr/lib/postgresql/9.2/bin/postgres \
    -D /var/lib/postgresql/9.2/main \
    -c config_file=/etc/postgresql/9.2/main/postgresql.conf')

Connect the PostgreSQL server using psql.

CONTAINER_IP=$(docker inspect $CONTAINER | grep IPAddress | awk '{ print $2 }' | tr -d ',"')
psql -h $CONTAINER_IP -p 5432 -d docker -U docker -W

As before, create roles or databases if needed.

psql (9.2.4)
Type "help" for help.

docker=# CREATE DATABASE foo OWNER=docker;
CREATE DATABASE

Additionally, publish there your newly created image on Docker Index.

docker login
Username: <your username>
[...]
docker push <your username>/postgresql

PostgreSQL service auto-launch

Running our image seems complicated. We have to specify the whole command with docker run. Let's simplify it so the service starts automatically when the container starts.

docker commit <container_id> <your username>/postgresql -run='{"Cmd": \
  ["/bin/su", "postgres", "-c", "/usr/lib/postgresql/9.2/bin/postgres -D \
  /var/lib/postgresql/9.2/main -c \
  config_file=/etc/postgresql/9.2/main/postgresql.conf"], PortSpecs": ["5432"]}

From now on, just type docker run <your username>/postgresql and PostgreSQL should automatically start.

Summary

We learnt how to use zaiste/postgresql image to launch PostgreSQL server on Docker and how to create the exact same image manually. In the next article, I'll show how to simplify the process of creating a Docker image using a Dockerfile.

You can discuss this post on HN.

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