gh-poindexter12-waypoint-technologies/skills/docker/references/volumes.md

Docker Volumes Reference

Volume Types

Named Volumes (Recommended)

Managed by Docker, stored in /var/lib/docker/volumes/.

volumes:
  db-data:

services:
  db:
    volumes:
      - db-data:/var/lib/mysql

Benefits:

• Portable across hosts
• Backup-friendly
• No permission issues
• Can use volume drivers (NFS, etc.)

Bind Mounts

Direct host path mapping.

services:
  web:
    volumes:
      - ./config:/etc/app/config:ro
      - /host/data:/container/data

Benefits:

• Direct file access from host
• Development workflow (live reload)
• Access to host files

Drawbacks:

• Host-dependent paths
• Permission issues possible
• Less portable

tmpfs Mounts

In-memory storage (Linux only).

services:
  app:
    tmpfs:
      - /tmp
      - /run:size=100m

Benefits:

• Fast (RAM-based)
• Secure (not persisted)
• Good for secrets, cache

Volume Options

Read-Only

volumes:
  - ./config:/etc/app/config:ro

Bind Propagation

volumes:
  - type: bind
    source: ./data
    target: /data
    bind:
      propagation: rslave

Volume Driver Options

volumes:
  nfs-data:
    driver: local
    driver_opts:
      type: nfs
      o: addr=192.168.1.100,rw
      device: ":/export/data"

Common Patterns

Database Data

services:
  postgres:
    image: postgres:15
    volumes:
      - pgdata:/var/lib/postgresql/data
    environment:
      POSTGRES_PASSWORD: secret

volumes:
  pgdata:

Configuration Files

services:
  nginx:
    image: nginx:alpine
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
      - ./html:/usr/share/nginx/html:ro

Shared Data Between Services

services:
  app:
    volumes:
      - shared:/data

  worker:
    volumes:
      - shared:/data

volumes:
  shared:

Log Persistence

services:
  app:
    volumes:
      - logs:/var/log/app

volumes:
  logs:

Backup and Restore

Backup Named Volume

# Create backup
docker run --rm \
  -v myvolume:/source:ro \
  -v $(pwd):/backup \
  alpine tar czf /backup/myvolume.tar.gz -C /source .

# Restore backup
docker run --rm \
  -v myvolume:/target \
  -v $(pwd):/backup \
  alpine tar xzf /backup/myvolume.tar.gz -C /target

Copy Files from Volume

docker cp <container>:/path/to/file ./local-file

Volume Management

# List volumes
docker volume ls

# Inspect volume
docker volume inspect <volume>

# Remove unused volumes
docker volume prune

# Remove specific volume
docker volume rm <volume>

# Create volume manually
docker volume create --name myvolume

Permissions

Common Permission Issues

# Check container user
docker exec <container> id

# Check volume permissions
docker exec <container> ls -la /data

Solutions

# Run as specific user
services:
  app:
    user: "1000:1000"
    volumes:
      - ./data:/data

Or fix host permissions:

chown -R 1000:1000 ./data

Best Practices

1. Use named volumes for data - More portable than bind mounts
2. Read-only when possible - Use :ro for config files
3. Separate concerns - Different volumes for data, config, logs
4. Backup strategy - Plan for volume backup/restore
5. Don't store in image - Data should be in volumes, not image layers
6. Use .dockerignore - Exclude data directories from build context