Bind mounts - Amazon Elastic Container Service

Bind mounts

With bind mounts, a file or directory on a host, such as an Amazon EC2 instance or AWS Fargate, is mounted into a container. Bind mounts are supported for tasks hosted on both Fargate and Amazon EC2 instances. By default, bind mounts are tied to the lifecycle of the container using them. Once all containers using a bind mount are stopped, for example when a task is stopped, the data is removed. For tasks hosted on Amazon EC2 instances, the data can be tied to the lifecycle of the host Amazon EC2 instance by specifying a host and optional sourcePath value in your task definition. For more information, see Using bind mounts in the Docker documentation.

The following are common use cases for bind mounts.

  • To provide an empty data volume to mount in one or more containers.

  • To mount a host data volume in one or more containers.

  • To share a data volume from a source container with other containers in the same task.

  • To expose a path and its contents from a Dockerfile to one or more containers.

Considerations when using bind mounts

When using bind mounts, the following should be considered.

  • For tasks hosted on AWS Fargate using platform version 1.4.0 or later, by default they receive a minimum of 20 GiB of ephemeral storage for bind mounts. The total amount of ephemeral storage can be increased to a maximum of 200 GiB by specifying the ephemeralStorage object in your task definition.

  • To expose files from a Dockerfile to a data volume when a task is run, the Amazon ECS data plane looks for a VOLUME directive. If the absolute path specified in the VOLUME directive is the same as the containerPath specified in the task definition, the data in the VOLUME directive path is copied to the data volume. In the following Dockerfile example, a file named examplefile in the /var/log/exported directory is written to the host and then mounted inside the container.

    FROM public.ecr.aws/amazonlinux/amazonlinux:latest RUN mkdir -p /var/log/exported RUN touch /var/log/exported/examplefile VOLUME ["/var/log/exported"]

    By default, the volume permissions are set to 0755 and the owner as root. These permissions can be customized in the Dockerfile. The following example defines the owner of the directory as node.

    FROM public.ecr.aws/amazonlinux/amazonlinux:latest RUN yum install -y shadow-utils && yum clean all RUN useradd node RUN mkdir -p /var/log/exported && chown node:node /var/log/exported RUN touch /var/log/exported/examplefile USER node VOLUME ["/var/log/exported"]
  • For tasks hosted on Amazon EC2 instances, when a host and sourcePath value are not specified, 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 beyond the lifecycle of the container, specify a sourcePath value for the bind mount.

Specifying a bind mount in your task definition

For Amazon ECS tasks hosted on either Fargate or Amazon EC2 instances, the following task definition JSON snippet shows the syntax for the volumes, mountPoints, and ephemeralStorage objects for a task definition.

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

For Amazon ECS tasks hosted on Amazon EC2 instances, you can use the optional host parameter and a sourcePath when specifying the task volume details, which when specified ties the bind mount to the lifecycle of the task rather than the container.

"volumes" : [ { "host" : { "sourcePath" : "string" }, "name" : "string" } ]

The following describes each task definition parameter in more detail.

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 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.

ephemeralStorage

Type: Object

Required: No

The amount of ephemeral storage to allocate for the task. This parameter is used to expand the total amount of ephemeral storage available, beyond the default amount, for tasks hosted on AWS Fargate using platform version 1.4.0 or later.

You can use the Copilot CLI, CloudFormation, the AWS SDK or the CLI to specify ephemeral storage for a bind mount.

Bind mount examples

The following examples cover the most common use cases for using a bind mount for your containers.

To allocate an increased amount of ephemeral storage space for a Fargate task

For Amazon ECS tasks hosted on Fargate using platform version 1.4.0 or later, you can allocate more than the default amount of ephemeral storage for the containers in your task to use. This example can be incorporated into the other examples to allocate more ephemeral storage for your Fargate tasks.

  • In the task definition, define an ephemeralStorage object. The sizeInGiB must be an integer between the values of 21 and 200 and is expressed in GiB.

    "ephemeralStorage": { "sizeInGiB": integer }

To provide an empty data volume for one or more containers

In some cases, you want to provide the containers in a task some scratch space. For example, you may have two database containers that need to access the same scratch file storage location during a task. This can be achieved using a bind mount.

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

    "volumes": [ { "name": "database_scratch", } ]
  2. In the containerDefinitions section, create the database container definitions so that they mount the volume.

    "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 expose a path and its contents in a Dockerfile to a container

In this example, you have a Dockerfile that writes data that you want to mount inside a container. This example works for tasks hosted on Fargate or Amazon EC2 instances.

  1. Create a Dockerfile. The following example uses the public Amazon Linux 2 container image and creates a file named examplefile in the /var/log/exported directory that we want to mount inside the container. The VOLUME directive should specify an absolute path.

    FROM public.ecr.aws/amazonlinux/amazonlinux:latest RUN mkdir -p /var/log/exported RUN touch /var/log/exported/examplefile VOLUME ["/var/log/exported"]

    By default, the volume permissions are set to 0755 and the owner as root. These permissions can be changed in the Dockerfile. In the following example, the owner of the /var/log/exported directory is set to node.

    FROM public.ecr.aws/amazonlinux/amazonlinux:latest RUN yum install -y shadow-utils && yum clean all RUN useradd node RUN mkdir -p /var/log/exported && chown node:node /var/log/exported RUN touch /var/log/exported/examplefile USER node VOLUME ["/var/log/exported"]
  2. In the task definition volumes section, define a volume with the name application_logs.

    "volumes": [ { "name": "application_logs", } ]
  3. In the containerDefinitions section, create the application container definitions so they mount the storage. The containerPath value must match the absolute path specified in the VOLUME directive from the Dockerfile.

    "containerDefinitions": [ { "name": "application1", "image": "my-repo/application", "cpu": 100, "memory": 100, "essential": true, "mountPoints": [ { "sourceVolume": "application_logs", "containerPath": "/var/log/exported" } ] }, { "name": "application2", "image": "my-repo/application", "cpu": 100, "memory": 100, "essential": true, "mountPoints": [ { "sourceVolume": "application_logs", "containerPath": "/var/log/exported" } ] } ]

To provide an empty data volume for a container that is tied to the lifecycle of the host Amazon EC2 instance

For tasks hosted on Amazon EC2 instances, you can use bind mounts and have the data tied to the lifecycle of the host Amazon EC2 instance rather than the containers referencing the volume. This is done by using the host parameter and specifying a sourcePath value. 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 host Amazon EC2 instance.

Important

Amazon ECS doesn't sync your storage across Amazon EC2 instances. Tasks that use persistent storage can be placed on any Amazon EC2 instance in your cluster that has available capacity. If your tasks require persistent storage after stopping and restarting, you should always specify the same Amazon EC2 instance at task launch time with the AWS CLI start-task command. You can also use Amazon EFS volumes for persistent storage. For more information, see Amazon EFS volumes.

  1. In the task definition volumes section, define a bind mount with name and sourcePath values. In the following example, the host Amazon EC2 instance contains data at /ecs/webdata that you want to mount inside the container.

    "volumes": [ { "name": "webdata", "host": { "sourcePath": "/ecs/webdata" } } ]
  2. In the containerDefinitions section, define a container with a mountPoints value that references the name of the 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 at different locations

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.