Data Management in Docker
Introduction
Docker containers are temporary and ephemeral, meaning any data stored inside a running container disappears when the container stops. To persist data across container restarts, Docker provides two primary storage options:
1. Volumes (Recommended) – Managed by Docker.
2. Bind Mounts – Directly link a folder from the host machine to a container.
1️. Using Docker Volumes (Recommended for Persistence)
What are Volumes?
• Stored in Docker’s managed directory (/var/lib/docker/volumes/).
• Can be shared between multiple containers.
• Persist even after a container is removed.
Basic Volume Commands
✅ Create a volume:
docker volume create my_volume
✅ Run a container with a volume:
docker run -d -v my_volume:/app/data ubuntu
✅ List all volumes:
docker volume ls
✅ Inspect a volume:
docker volume inspect my_volume
✅ Remove a volume:
docker volume rm my_volume
✅ Remove all unused volumes:
docker volume prune
2️⃣ Using Bind Mounts (Direct Host Folder Access)
What are Bind Mounts?
• Mounts a specific host machine directory inside the container.
• Changes inside the container also reflect on the host.
• Requires an absolute path on the host.
✅ Run a container with a bind mount:
docker run -d -v /home/user/data:/app/data ubuntu
Example:
If a file is added to /home/user/data on the host, it appears inside /app/data in the container.
3️⃣ Anonymous Volumes (Temporary Storage)
• Used for short-lived storage.
• Automatically created without a name.
Example:
docker run -d -v /app/data ubuntu
4️⃣ Managing Data in Docker Compose
Docker Compose allows defining persistent storage in docker-compose.yml:
aml
version: ‘3’
servicyes:
app:
image: ubuntu
volumes:
– my_volume:/app/data
volumes:
my_volume:
✅ Run Docker Compose:
docker-compose up -d
5️. Backing Up and Restoring Data
✅ Backup a volume:
docker run –rm -v my_volume:/data -v $(pwd):/backup ubuntu tar czf /backup/backup.tar.gz -C /data.
✅ Restore a volume:
docker run –rm -v my_volume:/data -v $(pwd):/backup ubuntu tar xzf /backup/backup.tar.gz -C /data
Conclusion
• Use Volumes for persistent storage across containers.
• Use Bind Mounts for direct access to host machine files.
• Always backup important container data to prevent loss.
