Docker Volumes

When using Docker volumes, the built-in local driver or a third-party volume driver can be used. Docker volumes are managed by Docker and a directory is created in /var/lib/docker/volumes on the container instance that contains the volume data.

To use Docker volumes, specify a dockerVolumeConfiguration in your task definition. For more information, see Using Volumes.

Some common use cases for Docker volumes are:

To provide persistent data volumes for use with containers
To share a defined data volume at different locations on different containers on the same container instance
To define an empty, nonpersistent data volume and mount it on multiple containers within the same task
To provide a data volume to your task that is managed by a third-party driver

Docker Volume Considerations

The following should be considered when using Docker volumes:

Docker volumes are only supported when using the EC2 launch type.
Windows containers only support the use of the local driver.
If a third-party driver is used, it should be installed and active on the container instance prior to the container agent starting. If the third-party driver is not active prior to the agent starting, you can restart the container agent using one of the following commands:
- For the Amazon ECS-optimized Amazon Linux 2 AMI:
```
sudo systemctl restart ecs
```
- For the Amazon ECS-optimized Amazon Linux AMI:
```
sudo stop ecs && sudo start ecs
```

Specifying a Docker Volume in your Task Definition

Before your containers can use data volumes, you must specify the volume and mount point configurations in your task definition. This section describes the volume configuration for a container. For tasks that use a Docker volume, specify a dockerVolumeConfiguration. For tasks that use a bind mount host volume, specify a host and optional sourcePath.

The task definition JSON shown below shows the syntax for the volumes and mountPoints objects for a container.


{
    "containerDefinitions": [
        {
            "mountPoints": [
                {
                    "sourceVolume": "string",
                    "containerPath": "/path/to/mount_volume",
                    "readOnly": boolean
                }
            ]
        }
    ],
    "volumes": [
        {
            "name": "string",
            "dockerVolumeConfiguration": {
                "scope": "string",
                "autoprovision": boolean,
                "driver": "string",
                "driverOpts": {
                    "key": "value"
                },
                "labels": {
                    "key": "value"
                }
            }
        }
    ]
}

name

Type: String

Required: No

The name of the volume. Up to 255 letters (uppercase and lowercase), numbers, hyphens, and underscores are allowed. This name is referenced in the sourceVolume parameter of container definition mountPoints.

dockerVolumeConfiguration

Type: Object

Required: No

This parameter is specified when using Docker volumes. Docker volumes are only supported when using the EC2 launch type. Windows containers only support the use of the local driver. To use bind mounts, specify a host instead.

scope

Type: String

Valid Values: task | shared

Required: No

The scope for the Docker volume, which determines its lifecycle. Docker volumes that are scoped to a task are automatically provisioned when the task starts destroyed when the task is cleaned up. Docker volumes that are scoped as shared persist after the task stops.

autoprovision

Type: Boolean

Default value: false

Required: No

If this value is true, the Docker volume is created if it does not already exist. This field is only used if the scope is shared. If the scope is task then this parameter must either be omitted or set to false.

driver

Type: String

Required: No

The Docker volume driver to use. The driver value must match the driver name provided by Docker because it is used for task placement. If the driver was installed using the Docker plugin CLI, use docker plugin ls to retrieve the driver name from your container instance. If the driver was installed using another method, use Docker plugin discovery to retrieve the driver name. For more information, see Docker plugin discovery. This parameter maps to Driver in the Create a volume section of the Docker Remote API and the --driver option to docker volume create.

driverOpts

Type: String

Required: No

A map of Docker driver specific options to pass through. This parameter maps to DriverOpts in the Create a volume section of the Docker Remote API and the --opt option to docker volume create.

labels

Type: String

Required: No

Custom metadata to add to your Docker volume. This parameter maps to Labels in the Create a volume section of the Docker Remote API and the --label option to docker volume create.

mountPoints

Type: Object Array

Required: No

The mount points for data volumes in your container.

This parameter maps to Volumes in the Create a container section of the Docker Remote API and the --volume option to docker run.

Windows containers can mount whole directories on the same drive as $env:ProgramData. Windows containers cannot mount directories on a different drive, and mount point cannot be across drives.

sourceVolume

Type: String

Required: Yes, when mountPoints are used

The name of the volume to mount.

containerPath

Type: String

Required: Yes, when mountPoints are used

The path on the container to mount the volume at.

readOnly

Type: Boolean

Required: No

If this value is true, the container has read-only access to the volume. If this value is false, then the container can write to the volume. The default value is false.

Examples

The following are examples showing the use of Docker volumes.

To provide nonpersistent storage for a container using a Docker volume

In this example, you want a container to use an empty data volume that you aren't interested in keeping after the task has finished. For example, you may have a container that needs to access some scratch file storage location during a task. This task can be achieved using a Docker volume.

In the task definition volumes section, define a data volume with name and DockerVolumeConfiguration values. In this example, we specify the scope as task so the volume is deleted after the task stops and use the built-in local driver.
```
"volumes": [
    {
        "name": "scratch",
        "dockerVolumeConfiguration" : {
            "scope": "task",
            "driver": "local",
            "labels": {
                "scratch": "space"
            }
        }
    }
]
```
In the containerDefinitions section, define a container with mountPoints values that reference the name of the defined volume and the containerPath value to mount the volume at on the container.
```
"containerDefinitions": [
    {
        "name": "container-1",
        "mountPoints": [
            {
              "sourceVolume": "scratch",
              "containerPath": "/var/scratch"
            }
        ]
    }
]
```

To provide persistent storage for a container using a Docker volume

In this example, you want a shared volume for multiple containers to use and you want it to persist after any single task using it has stopped. The built-in local driver is being used so the volume is still tied to the lifecycle of the container instance.

In the task definition volumes section, define a data volume with name and DockerVolumeConfiguration values. In this example, specify a shared scope so the volume persists, set autoprovision to true so that the volume is created for use, and use the built-in local driver.
```
"volumes": [
    {
        "name": "database",
        "dockerVolumeConfiguration" : {
            "scope": "shared",
            "autoprovision": true,
            "driver": "local",
            "labels": {
                "database": "database_name"
            }
        }
    }
]
```

In the containerDefinitions section, define a container with mountPoints values that reference the name of the defined volume and the containerPath value to mount the volume at on the container.


"containerDefinitions": [
    {
        "name": "container-1",
        "mountPoints": [
        {
          "sourceVolume": "database",
          "containerPath": "/var/database"
        }
      ]
    },
    {
      "name": "container-2",
      "mountPoints": [
        {
          "sourceVolume": "database",
          "containerPath": "/var/database"
        }
      ]
    }
  ]

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