AWS Documentation » Amazon ECS » Developer Guide » Amazon ECS Task Definitions » Using Data Volumes in Tasks » Bind Mounts

Bind Mounts

With bind mounts, a file or directory on the host machine is mounted into a container. Bind mount host volumes are supported when using either the EC2 or Fargate launch types. Fargate tasks only support nonpersistent storage volumes, so the host and sourcePath fields are not supported. For more information, see Fargate Task Storage.

To use bind mount host volumes with tasks using the EC2 launch type, specify a host and optional sourcePath value in your task definition. For more information, see Using bind mounts.

Some common use cases for bind mounts are:

• To provide persistent data volumes for use with containers

• To define an empty, nonpersistent data volume and mount it on multiple containers on the same container instance

• To share defined data volumes at different locations on different containers on the same container instance

Specifying a Bind Mount in your Task Definition

Before your containers can use bind mount host 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 bind mount host volume, specify a host value and optional sourcePath value.

The following task definition JSON snippet shows the syntax for the volumes and mountPoints objects for a container:

{
   "family": "",
   ...
   "containerDefinitions" : [
      {
         "mountPoints" : [
            {
               "containerPath" : "/path/to/mount_volume",
               "sourceVolume" : "string"
            }
          ],
          "name" : "string"
       }
    ],
    ...
    "volumes" : [
       {
          "host" : {
             "sourcePath" : "string"
          },
          "name" : "string"
       }
    ]
}             

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.

host

Required: No

This parameter is specified when using bind mounts. To use Docker volumes, specify a dockerVolumeConfiguration instead. The contents of the host parameter determine whether your bind mount data volume persists on the host container instance and where it is stored. If the host parameter is empty, then the Docker daemon assigns a host path for your data volume, but the data is not guaranteed to persist after the containers associated with it stop running.

Bind mount host volumes are supported when using either the EC2 or Fargate launch types.

Windows containers can mount whole directories on the same drive as $env:ProgramData.

sourcePath

Type: String

Required: No

When the host parameter is used, specify a sourcePath to declare the path on the host container instance that is presented to the container. If this parameter is empty, then the Docker daemon has assigned a host path for you. If the host parameter contains a sourcePath file location, then the data volume persists at the specified location on the host container instance until you delete it manually. If the sourcePath value does not exist on the host container instance, the Docker daemon creates it. If the location does exist, the contents of the source path folder are exported.

mountPoints

Type: Object

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

To provide nonpersistent empty storage for containers using a bind mount

In some cases, you want containers to share the same empty data volume, but you aren't interested in keeping the data after the task has finished. For example, you may have two database containers that need to access the same scratch file storage location during a task. This task can be achieved using either a Docker volume or a bind mount host volume.

1. In the task definition volumes section, define a bind mount with the name database_scratch.

   Note

   Because the database_scratch bind mount does not specify a source path, the Docker daemon manages the bind mount for you. When no containers reference this bind mount, the Amazon ECS container agent task cleanup service eventually deletes it (by default, this happens 3 hours after the container exits, but you can configure this duration with the ECS_ENGINE_TASK_CLEANUP_WAIT_DURATION agent variable). For more information, see Amazon ECS Container Agent Configuration. If you need this data to persist, specify a sourcePath value for the bind mount.

     "volumes": [
       {
         "name": "database_scratch",
         "host": {}
       }
     ]

2. In the containerDefinitions section, create the database container definitions so that they mount the nonpersistent storage.

     "containerDefinitions": [
       {
         "name": "database1",
         "image": "my-repo/database",
         "cpu": 100,
         "memory": 100,
         "essential": true,
         "mountPoints": [
           {
             "sourceVolume": "database_scratch",
             "containerPath": "/var/scratch"
           }
         ]
       },
       {
         "name": "database2",
         "image": "my-repo/database",
         "cpu": 100,
         "memory": 100,
         "essential": true,
         "mountPoints": [
           {
             "sourceVolume": "database_scratch",
             "containerPath": "/var/scratch"
           }
         ]
       }
     ]

To provide persistent storage for containers using a bind mount

When using bind mounts, if a sourcePath value is specified the data persists even after all containers that referenced it have stopped. Any files that exist at the sourcePath are presented to the containers at the containerPath value, and any files that are written to the containerPath value are written to the sourcePath value on the container instance.

Important

Amazon ECS does not sync your storage across container instances. Tasks that use persistent storage can be placed on any container instance in your cluster that has available capacity. If your tasks require persistent storage after stopping and restarting, you should always specify the same container instance at task launch time with the AWS CLI start-task command.

1. In the task definition volumes section, define a bind mount with name and sourcePath values.

     "volumes": [
       {
         "name": "webdata",
         "host": {
           "sourcePath": "/ecs/webdata"
         }
       }
     ]

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

     "containerDefinitions": [
       {
         "name": "web",
         "image": "nginx",
         "cpu": 99,
         "memory": 100,
         "portMappings": [
           {
             "containerPort": 80,
             "hostPort": 80
           }
         ],
         "essential": true,
         "mountPoints": [
           {
             "sourceVolume": "webdata",
             "containerPath": "/usr/share/nginx/html"
           }
         ]
       }
     ]

To mount a defined volume on multiple containers

You can define a data volume in a task definition and mount that volume at different locations on different containers. For example, your host container has a website data folder at /data/webroot, and you may want to mount that data volume as read-only on two different web servers that have different document roots.

1. In the task definition volumes section, define a data volume with the name webroot and the source path /data/webroot.

     "volumes": [
       {
         "name": "webroot",
         "host": {
           "sourcePath": "/data/webroot"
         }
       }
     ]

2. In the containerDefinitions section, define a container for each web server with mountPoints values that associate the webroot volume with the containerPath value pointing to the document root for that container.

     "containerDefinitions": [
       {
         "name": "web-server-1",
         "image": "my-repo/ubuntu-apache",
         "cpu": 100,
         "memory": 100,
         "portMappings": [
           {
             "containerPort": 80,
             "hostPort": 80
           }
         ],
         "essential": true,
         "mountPoints": [
           {
             "sourceVolume": "webroot",
             "containerPath": "/var/www/html",
             "readOnly": true
           }
         ]
       },
       {
         "name": "web-server-2",
         "image": "my-repo/sles11-apache",
         "cpu": 100,
         "memory": 100,
         "portMappings": [
           {
             "containerPort": 8080,
             "hostPort": 8080
           }
         ],
         "essential": true,
         "mountPoints": [
           {
             "sourceVolume": "webroot",
             "containerPath": "/srv/www/htdocs",
             "readOnly": true
           }
         ]
       }
     ]

To mount volumes from another container using volumesFrom

You can define one or more volumes on a container, and then use the volumesFrom parameter in a different container definition (within the same task) to mount all of the volumes from the sourceContainer at their originally defined mount points. The volumesFrom parameter applies to volumes defined in the task definition, and those that are built into the image with a Dockerfile.

1. (Optional) To share a volume that is built into an image, you need to build the image with the volume declared in a VOLUME instruction. The following example Dockerfile uses an httpd image and then adds a volume and mounts it at dockerfile_volume in the Apache document root (which is the folder used by the httpd web server):

   FROM httpd
   VOLUME ["/usr/local/apache2/htdocs/dockerfile_volume"]

   You can build an image with this Dockerfile and push it to a repository, such as Docker Hub, and use it in your task definition. The example my-repo/httpd_dockerfile_volume image used in the following steps was built with the above Dockerfile.

2. Create a task definition that defines your other volumes and mount points for the containers. In this example volumes section, you create an empty volume called empty, which the Docker daemon manages. There is also a host volume defined called host_etc, which exports the /etc folder on the host container instance.

   {
     "family": "test-volumes-from",
     "volumes": [
       {
         "name": "empty",
         "host": {}
       },
       {
         "name": "host_etc",
         "host": {
           "sourcePath": "/etc"
         }
       }
     ],

   In the container definitions section, create a container that mounts the volumes defined earlier. In this example, the web container (which uses the image built with a volume in the Dockerfile) mounts the empty and host_etc volumes.

   "containerDefinitions": [
       {
         "name": "web",
         "image": "my-repo/httpd_dockerfile_volume",
         "cpu": 100,
         "memory": 500,
         "portMappings": [
           {
             "containerPort": 80,
             "hostPort": 80
           }
         ],
         "mountPoints": [
           {
             "sourceVolume": "empty",
             "containerPath": "/usr/local/apache2/htdocs/empty_volume"
           },
           {
             "sourceVolume": "host_etc",
             "containerPath": "/usr/local/apache2/htdocs/host_etc"
           }
         ],
         "essential": true
       },

   Create another container that uses volumesFrom to mount all of the volumes that are associated with the web container. All of the volumes on the web container are likewise mounted on the busybox container (including the volume specified in the Dockerfile that was used to build the my-repo/httpd_dockerfile_volume image).

       {
         "name": "busybox",
         "image": "busybox",
         "volumesFrom": [
           {
             "sourceContainer": "web"
           }
         ],
         "cpu": 100,
         "memory": 500,
         "entryPoint": [
           "sh",
           "-c"
         ],
         "command": [
           "echo $(date) > /usr/local/apache2/htdocs/empty_volume/date && echo $(date) > /usr/local/apache2/htdocs/host_etc/date && echo $(date) > /usr/local/apache2/htdocs/dockerfile_volume/date"
         ],
         "essential": false
       }
     ]
   }

   When this task is run, the two containers mount the volumes, and the command in the busybox container writes the date and time to a file called date in each of the volume folders. The folders are then visible at the website displayed by the web container.

   Note

   Because the busybox container runs a quick command and then exits, it must be set as "essential": false in the container definition. Otherwise, it stops the entire task when it exits.