Container Volumes

For each volume a container specifies (i.e., ContainerInfo.volumes), the following fields must be specified:

• container_path: Path in the container filesystem at which the volume will be mounted. If the path is a relative path, it is relative to the container’s sandbox.

• mode: If the volume is read-only or read-write.

• source: Describe where the volume originates from. See more details in the following section.

Volume Source Types

• HOST_PATH
• SANDBOX_PATH
• DOCKER_VOLUME
• SECRET

HOST_PATH Volume Source

This volume source represents a path on the host filesystem. The path can either point to a directory or a file (either a regular file or a device file).

The following example shows a HOST_PATH volume that mounts /var/lib/mysql on the host filesystem to the same location in the container.

{
  "container_path": "/var/lib/mysql",
  "mode": "RW",
  "source": {
    "type": "HOST_PATH",
    "host_path": {
      "path": "/var/lib/mysql"
    }
  }
}

The mode and ownership of the volume will be the same as that on the host filesystem.

If you are using the Mesos Containerizer, HOST_PATH volumes are handled by the volume/host_path isolator. To enable this isolator, append volume/host_path to the --isolation flag when starting the agent. This isolator depends on the filesystem/linux isolator.

Docker Containerizer supports HOST_PATH volume as well.

SANDBOX_PATH Volume Source

There are currently two types of SANDBOX_PATH volume sources: SELF and PARENT.

If you are using Mesos Containerizer, SANDBOX_PATH volumes are handled by the volume/sandbox_path isolator. To enable this isolator, append volume/sandbox_path to the --isolation flag when starting the agent.

The Docker Containerizer only supports SELF type SANDBOX_PATH volumes currently.

SELF Type

This represents a path in the container’s own sandbox. The path can point to either a directory or a file in the sandbox of the container.

The following example shows a SANDBOX_PATH volume from the container’s own sandbox that mount the subdirectory tmp in the sandbox to /tmp in the container root filesystem. This will be useful to cap the /tmp usage in the container (if disk isolator is used and --enforce_container_disk_quota is turned on).

{
  "container_path": "/tmp",
  "mode": "RW",
  "source": {
    "type": "SANDBOX_PATH",
    "sandbox_path": {
      "type": "SELF",
      "path": "tmp"
    }
  }
}

The ownership of the volume will be the same as that of the sandbox of the container.

Note that container_path has to be an absolute path in this case. If container_path is relative, that means it’s a volume from a subdirectory in the container sandbox to another subdirectory in the container sandbox. In that case, the user can just create a symlink, instead of using a volume.

PARENT Type

This represents a path in the sandbox of the parent container. The path can point to either a directory or a file in the sandbox of the parent container. See the nested container doc for more details about what a parent container is.

The following example shows a SANDBOX_PATH volume from the sandbox of the parent container that mounts the subdirectory shared_volume in the sandbox of the parent container to subdirectory volume in the sandbox of the container.

{
  "container_path": "volume",
  "mode": "RW",
  "source": {
    "type": "SANDBOX_PATH",
    "sandbox_path": {
      "type": "PARENT",
      "path": "shared_volume"
    }
  }
}

The ownership of the volume will be the same as that of the sandbox of the parent container.

DOCKER_VOLUME Volume Source

See more details in this doc.

SECRET Volume Source

See more details in this doc.