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07-volumes.md

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Volumes top-level element

Volumes are persistent data stores implemented by the platform. The Compose specification offers a neutral abstraction for services to mount volumes, and configuration parameters to allocate them on infrastructure.

The volumes section allows the configuration of named volumes that can be reused across multiple services. Here's an example of a two-service setup where a database's data directory is shared with another service as a volume named db-data so that it can be periodically backed up:

services:
  backend:
    image: awesome/database
    volumes:
      - db-data:/etc/data

  backup:
    image: backup-service
    volumes:
      - db-data:/var/lib/backup/data

volumes:
  db-data:

An entry under the top-level volumes key can be empty, in which case it uses the platform's default configuration for creating a volume. Optionally, you can configure it with the following keys:

driver

Specify which volume driver should be used for this volume. Default and available values are platform specific. If the driver is not available, the Compose implementation MUST return an error and stop application deployment.

driver: foobar

driver_opts

driver_opts specifies a list of options as key-value pairs to pass to the driver for this volume. Those options are driver-dependent.

volumes:
  example:
    driver_opts:
      type: "nfs"
      o: "addr=10.40.0.199,nolock,soft,rw"
      device: ":/docker/example"

external

If set to true, external specifies that this volume already exist on the platform and its lifecycle is managed outside of that of the application. Compose implementations MUST NOT attempt to create these volumes, and MUST return an error if they do not exist.

If external is set to true and volume configuration has other but name attributes set, considering resource is not managed by compose lifecycle, Compose Implementations SHOULD reject a Compose file as invalid.

In the example below, instead of attempting to create a volume called {project_name}_db-data, Compose looks for an existing volume simply called db-data and mounts it into the backend service's containers.

services:
  backend:
    image: awesome/database
    volumes:
      - db-data:/etc/data

volumes:
  db-data:
    external: true

labels

labels are used to add metadata to volumes. You can use either an array or a dictionary.

It's recommended that you use reverse-DNS notation to prevent your labels from conflicting with those used by other software.

labels:
  com.example.description: "Database volume"
  com.example.department: "IT/Ops"
  com.example.label-with-empty-value: ""
labels:
  - "com.example.description=Database volume"
  - "com.example.department=IT/Ops"
  - "com.example.label-with-empty-value"

Compose implementation MUST set com.docker.compose.project and com.docker.compose.volume labels.

name

name set a custom name for this volume. The name field can be used to reference volumes that contain special characters. The name is used as is and will not be scoped with the stack name.

volumes:
  data:
    name: "my-app-data"

It can also be used in conjunction with the external property. Doing so the name of the volume used to lookup for actual volume on platform is set separately from the name used to refer to it within the Compose file:

volumes:
  db-data:
    external:
      name: actual-name-of-volume

This make it possible to make this lookup name a parameter of a Compose file, so that the model ID for volume is hard-coded but the actual volume ID on platform is set at runtime during deployment:

volumes:
  db-data:
    external:
      name: ${DATABASE_VOLUME}