Add a Postgres Database With Docker to Your Project

I prefer to use Docker containers for running a PostgreSQL database.

Spin up the container, develop the app, then tear down the container. The Postgres database doesn't clutter up my local system, and I can easily set it up on a different machine.

Using Docker Compose, I can configure the setup and commit it to source control.

In this blog post, I'll show you how to get a database up and running with Docker and Docker Compose.

Prerequisites:

• Docker
• Docker Compose

Postgres with Docker Compose

Docker Compose allows you to write yaml files that are easy to read for humans and serve as instructions for Docker.

Go to the project folder of your application and create a new file: docker-compose.yaml.

version: '2.4'

services:
  db:
    build:
      context: ./db
      dockerfile: Dockerfile
    ports:
      - 5432:5432
    environment:
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres
    volumes:
      - db-data:/var/lib/postgresql/data:delegated

volumes:
  db-data:

We create a new service called db (you can call it whatever you want).

The container runs on port 5432. Docker exposes that port on localhost:5432.

You need to map the port inside the container to the host machine (your development computer).

Otherwise, your app won't be able to connect to the Postgres database.

We also use some environment variables for the user and password.

What's the deal with volumes?

Volumes are the preferred mechanism for persisting data generated by and used by Docker containers. ¹

If you specify volumes in the docker-compose.yml file, Compose preserves the volume:

When docker-compose up runs, if it finds any containers from previous runs, it copies the volumes from the old container to the new container. This process ensures that any data you’ve created in volumes isn’t lost. ²

The empty top-level entry tells Compose that the utility should use the default driver for your machine.

volumes:
  db-data:

Create a Dockerfile

We told Compose that there will be a Dockerfile in the db directory.

Example folder structure:

.
├── db
│   ├── init.sql
│   └── Dockerfile
├── docker-compose.yml
└── app

If you have a different folder structure, you need to adjust docker-compose.yml's context entry. At the moment, Docker looks for the db directory in the root folder:

services:
  db:
    build:
      context: ./db

Create the db directory and the Dockerfile:

# pull official base image
FROM postgres:12.2-alpine

# run init.sql
ADD init.sql /docker-entrypoint-initdb.d

(See Docker Hub for alternative images.)

Now we can use init.sql to populate the database. We use a simple script that creates a new database called task_management.

init.sql:

CREATE DATABASE task_management;

I manage schema creation within my app in the language of my choice. For example, I use TypeORM (TypeScript) or SQLAlchemy (Python), depending on the web framework I'm using.

Container Commands

Now you can run the database. Inside the root directory, open the terminal and type:

docker-compose up -d

The command will start the container in detached mode (in the background).

If you want to use the command line to connect to the database:

docker-compose exec db psql -U postgres -d task_management

• docker-compose exec: execute a command inside a running container
• db: name of the service (see configuration in docker-compose.yml)
• psql: terminal command to run, see psql
• -U postgres: user name is postgres
• -d task_management: connect to the database called task_management

Alternatively, you can use a GUI tool like pgAdmin or DBeaver.

Recap

You've seen how to create a simple configuration for Docker and Docker Compose that will create a Postgres container.

Now you can use the database for local development of your application.

Further Reading

• Database in a Docker container — how to start and what’s it about by Wojciech Krzywiec
• Docker Hub: Official postgres image

1. from docs.docker.com ↩

2. from docs.docker.com ↩