How to Manage and Migrate Docker Volumes for PostgreSQL

Docker volumes are essential for maintaining data persistence in containerized applications. This guide will explain how to configure Docker volumes for a PostgreSQL container, and how to migrate this data to another computer or cloud instance.

Configuring Docker Volumes in docker-compose.yml

Here's an example of a docker-compose.yml file that sets up a PostgreSQL container with a Docker volume:

services:
  db:
    image: postgres:12
    restart: always
    volumes:
      - app-db-data:/var/lib/postgresql/data/pgdata
    env_file:
      - .env
    environment:
      - PGDATA=/var/lib/postgresql/data/pgdata
      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD?Variable not set}
      - POSTGRES_USER=${POSTGRES_USER?Variable not set}
      - POSTGRES_DB=${POSTGRES_DB?Variable not set}

volumes:
  app-db-data:

Explanation

• image: Specifies the PostgreSQL image version.
• restart: Ensures the container always restarts on failure.
• volumes: Mounts the app-db-data volume to the PostgreSQL data directory.
• env_file: Loads environment variables from a .env file.
• environment: Sets environment variables for PostgreSQL configuration.

Volumes

The volumes section defines a named volume app-db-data:

volumes:
  app-db-data:

This volume is managed by Docker and ensures data persists even if the container is removed or restarted.

Data Persistence

Docker volumes store data on the host system, typically under /var/lib/docker/volumes/. The data in app-db-data is mounted to /var/lib/postgresql/data/pgdata inside the container, ensuring PostgreSQL data is stored persistently.

Migrating Docker Volumes

To move Docker volume data to another computer or cloud instance, follow these steps:

1. Backup Volume Data

Run the following command to back up the volume data to a tar file:

docker run --rm -v app-db-data:/volume -v $(pwd):/backup alpine tar czf /backup/app-db-data.tar.gz -C /volume .

2. Transfer Backup File

Use scp, rsync, or a cloud provider's file transfer tool to move the backup file to the destination:

scp app-db-data.tar.gz user@remote_host:/path/to/destination

3. Restore Volume Data

On the destination machine, create a Docker volume and restore the data:

1. Create the volume:

docker volume create app-db-data

1. Restore the data:

docker run --rm -v app-db-data:/volume -v $(pwd):/backup alpine sh -c "tar xzf /backup/app-db-data.tar.gz -C /volume"

4. Start the Container

Use docker-compose to start the container with the restored volume:

docker-compose up

Conclusion

By following these steps, you can ensure your PostgreSQL data is persistent and can be migrated across different environments. Docker volumes provide a robust way to manage data in containerized applications, making it easier to maintain and transfer critical data.

Reference

Full Stack FastAPI Template