Volumes

Containers are ephemeral by design: when a container is removed, its writable layer — and any data written to it — is gone. Volumes are the mechanism Docker provides for persisting data beyond the lifetime of a container and for sharing data between containers.

Why You Need Volumes

Consider a database container. Every time you restart the container the database starts fresh unless you persist the data directory somewhere outside the container's writable layer. Volumes solve this by mounting a directory from outside the container into its filesystem.

There are three types of storage in Docker:

• Volumes — managed by Docker, stored in Docker's data directory on the host
• Bind mounts — map a specific directory on the host into the container
• tmpfs mounts — stored in memory only, never written to disk

Named Volumes

Named volumes are the recommended way to persist data in production. Docker manages where the data is stored on disk; you refer to the volume by name.

# Create a named volume
docker volume create my-data

# Run a container with the volume mounted at /data
docker run -d   --name my-app   -v my-data:/data   my-image

# List volumes
docker volume ls

# Inspect a volume (shows mount point on host)
docker volume inspect my-data

# Remove a volume (only if no containers are using it)
docker volume rm my-data

# Remove all unused volumes
docker volume prune

Bind Mounts

Bind mounts map a specific path on the host filesystem into the container. They are especially useful during development because changes you make to files on your host are immediately visible inside the container.

# Mount the current directory into /app inside the container
docker run --rm -it   -v $(pwd):/app   -w /app   node:20-alpine   sh

# The -v flag syntax: host-path:container-path
docker run -d   -v /host/config:/etc/myapp/config:ro   my-image

The :ro suffix makes the bind mount read-only inside the container, which prevents the container from accidentally modifying host files.

Database Persistence Example

# Run PostgreSQL with a named volume for data persistence
docker run -d   --name postgres   -e POSTGRES_PASSWORD=secret   -e POSTGRES_DB=mydb   -v postgres-data:/var/lib/postgresql/data   -p 5432:5432   postgres:16

# Stop and remove the container
docker stop postgres
docker rm postgres