Databáze řešení

By default, any data written inside a container disappears when that container is removed. Volumes solve this by storing data outside the container's writable layer, so it survives restarts, updates, and even complete container recreation.

Why This Matters

Database files, uploaded media, and configuration should never live only inside a container — running docker compose down or replacing a container for an image update would permanently destroy that data without a volume.

Named Volumes (Recommended for Most Cases)

Docker manages the storage location for you:

docker volume create app_data
docker run -d --name db -v app_data:/var/lib/mysql mysql:8.0

Listing and Inspecting Volumes

docker volume ls
docker volume inspect app_data

Bind Mounts (Mapping a Specific Host Directory)

Useful when you need direct access to the files from outside Docker (e.g. editing website files):

docker run -d --name web -v /home/deploy/site:/usr/share/nginx/html nginx

Named Volumes in Docker Compose

services:
  db:
    image: mysql:8.0
    volumes:
      - db_data:/var/lib/mysql

volumes:
  db_data:

Read-Only Mounts

For files a container should never modify:

docker run -v /home/deploy/site:/usr/share/nginx/html:ro nginx

Backing Up a Named Volume

docker run --rm \
  -v app_data:/data \
  -v $(pwd):/backup \
  alpine tar czf /backup/app_data-backup.tar.gz /data

Restoring a Named Volume

docker run --rm \
  -v app_data:/data \
  -v $(pwd):/backup \
  alpine sh -c "cd /data && tar xzf /backup/app_data-backup.tar.gz --strip 1"

Removing Unused Volumes

docker volume prune

This only removes volumes not currently referenced by any container — review the list first if the data might still be needed.

Named Volumes vs Bind Mounts

Common Errors

Data disappeared after recreating a container — the container was run without a volume; the data existed only in its writable layer and was lost on removal.

Permission denied writing to a bind mount — check the host directory's ownership matches the user the container process runs as.

Best Practices

• Always use a volume for databases and any state you can't afford to lose
• Prefer named volumes for portability; use bind mounts when you need direct host-side file access
• Include volume backups in your regular backup routine, not just database dumps

FAQ

Does docker compose down delete volumes?
No, not by default — only docker compose down -v also removes named volumes. Always double-check before adding -v.

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