How do I mount a host directory as a volume in docker compose

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From the looks of it you could do the following on your docker-compose.yml

volumes:    - ./:/app

Where ./ is the host directory, and /app is the target directory for the containers.

For the lazy – v3 / v2 / v1

Side note: Syntax remains the same for all versions as of this edit

There are a few options

Short Syntax

Using the host : guest format you can do any of the following:

volumes:  # Just specify a path and let the Engine create a volume  - /var/lib/mysql  # Specify an absolute path mapping  - /opt/data:/var/lib/mysql  # Path on the host, relative to the Compose file  - ./cache:/tmp/cache  # User-relative path  - ~/configs:/etc/configs/:ro  # Named volume  - datavolume:/var/lib/mysql

Long Syntax

As of docker-compose v3.2 you can use long syntax which allows the configuration of additional fields that can be expressed in the short form such as mount type (volume, bind or tmpfs) and read_only.

version: "3.2"services:  web:    image: nginx:alpine    ports:      - "80:80"    volumes:      - type: volume        source: mydata        target: /data        volume:          nocopy: true      - type: bind        source: ./static        target: /opt/app/staticnetworks:  webnet:volumes:  mydata:

Check out https://docs.docker.com/compose/compose-file/#long-syntax-3 for more info.

If you would like to mount a particular host directory (/disk1/prometheus-data in the following example) as a volume in the volumes section of the Docker Compose YAML file, you can do it as below, e.g.:

version: '3'services:  prometheus:    image: prom/prometheus    volumes:      - prometheus-data:/prometheusvolumes:  prometheus-data:    driver: local    driver_opts:      o: bind      type: none      device: /disk1/prometheus-data

By the way, in prometheus's Dockerfile, You may find the VOLUME instruction as below, which marks it as holding externally mounted volumes from native host, etc. (Note however: this instruction is not a must though to mount a volume into a container.):

Dockerfile

...VOLUME ["/prometheus"]...

Refs:

• https://docs.docker.com/compose/compose-file/#driver
• https://docs.docker.com/compose/compose-file/#driver_opts