Volumes and persistent data

Docker · lesson 10 of 31 · 3 min read

Keep data alive when a container is replaced, and know when a bind mount is the better tool.

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Key points

  • Containers are disposable. Anything written to the container filesystem dies with docker rm.
  • A named volume is Docker-managed storage that outlives containers. The right choice for databases.
  • A bind mount maps a host directory in. Perfect for local dev, awkward in production where paths and uids differ.
  • --mount is explicit and fails loudly on a typo. -v is shorter but silently invents directories.
  • Add ,readonly for config you never want the container to rewrite.

Example

docker volume create pgdata

# named volume: the data survives replacing the container
docker run -d --name db \
  --mount type=volume,src=pgdata,dst=/var/lib/postgresql/data \
  -e POSTGRES_PASSWORD=secret \
  postgres:16

# bind mount: a host directory, mounted read-only
docker run --rm \
  --mount type=bind,src="$PWD/config",dst=/app/config,readonly \
  myapp:1.0

docker volume ls
docker volume rm pgdata      # this deletes the data. no undo.

If it has to survive a redeploy, it belongs in a volume.

Environment variables and secrets Networks and service-to-service calls

This is a reading copy. The full lesson — with the visual explainer, the interactive lab and a Run button for the code — lives in the Docker course, and every lesson in it is listed on the Docker contents page.