Managing Docker volumes and networks

Managing Docker Volumes and Networks

This article explains how to manage Docker volumes and networks for persistent data and secure service communication in multi-container applications.

Prerequisites

- Docker Engine 24.0 or higher - Docker Compose V2 (built into Docker Desktop or installed separately) - Basic knowledge of Docker containers and `docker-compose.yml` - Terminal or CLI with the `docker` command available

Steps

1. Create a named volume for persistent data Use `docker volume create` instead of bind mounts. This gives Docker full control over storage. docker volume create mijn-data

2. Define volumes declaratively in docker-compose.yml Add a top-level `volumes` section and attach it to a service. This ensures reproducibility and clear separation.

volumes:
     db-data:
   
   services:
     database:
       image: postgres:16
       volumes:
         - db-data:/var/lib/postgresql/data

3. Create a user-defined bridge network Instead of the default network, use a named network for better DNS resolution and isolation.

networks:
     app-net:
       driver: bridge

4. Attach services to the network Specify which services should communicate with each other. A database does not need to be directly reachable from the outside world.

services:
     web:
       image: nginx:latest
       networks:
         - app-net
     database:
       image: postgres:16
       networks:
         - app-net

5. Isolate a network with `internal: true` Use this for databases or backend services that do not need internet access.

networks:
     internal-net:
       driver: bridge
       internal: true

6. Add a service to multiple networks An application service can, for example, be part of both a public and an internal network.

services:
     app:
       image: my-app:latest
       networks:
         - frontend-net
         - backend-net

7. Clean up unused volumes Volumes no longer attached to a container continue to take up disk space. Clean them up periodically. docker volume prune

8. Use volume plugins for multi-host setups For clusters (Docker Swarm, Kubernetes), use external storage via plugins. This enables volume migration between hosts.

volumes:
     shared-data:
       driver: nfs
       driver_opts:
         server: nfs-server.example.com
         path: /exports/data

Verification

Check that volumes are correctly created and networks are functioning:

List all volumes
docker volume ls
Inspect a volume
docker volume inspect mijn-data
Show networks and attached containers
docker network ls
docker network inspect app-net

Test DNS resolution between services: docker compose exec web ping database

Frequently Asked Problems

1. Container cannot find another service by hostname Cause: Services are not in the same user-defined network. Solution: Explicitly add both services to the same named network in `docker-compose.yml`.

2. Data disappears after container removal Cause: Use of container-internal storage instead of a volume. Solution: Define a named volume and attach it to the service. Committing containers is not a substitute.

3. Volume space runs out, but the container is still running Cause: Unused volumes remain. Solution: Run `docker volume prune` regularly or automate it in a cronjob. Add `--filter` to retain specific volumes.

Common errors arise from mixing bind mounts and volumes in the same application — choose one strategy and stick with it.