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Amazon EC2 Container Service
Developer Guide (API Version 2014-11-13)

Using Data Volumes in Tasks

There are several use cases for using data volumes in Amazon ECS task definitions. Some common examples 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, and to share defined data volumes at different locations on different containers on the same container instance.

Note

For operating systems that use devicemapper (such as Amazon Linux and the Amazon ECS-optimized AMI), only file systems that are available when the Docker daemon is started will be available to Docker containers. You can use a cloud boothook to mount your file system before the Docker daemon starts, or you can restart the Docker daemon and the Amazon ECS container agent after the file system is mounted to make the file system available to your container volume mounts.

To provide persistent data volumes for containers

When a volume is defined with a sourcePath value, the data volume 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 by running containers that mount the data volume are written to the sourcePath value on the container instance.

Important

Amazon ECS does not sync your data volumes across container instances. Tasks that use persistent data volumes can be placed on any container instance in your cluster that has available capacity. If your tasks require persistent data volumes 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 data volume with name and sourcePath values.

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    "volumes": [ { "name": "webdata", "host": { "sourcePath": "/ecs/webdata" } } ]
  2. In the containerDefinitions section, define a container with mountPoints that reference the name of the defined volume and the containerPath value to mount the volume at on the container.

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    "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 provide nonpersistent empty data volumes for containers

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.

  1. In the task definition volumes section, define a data volume with the name database_scratch.

    Note

    Because the database_scratch volume does not specify a source path, the Docker daemon manages the volume for you. When no containers reference this volume, 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 volume.

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

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    "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 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.

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    "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.

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    "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):

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    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 will manage. There is also a host volume defined called host_etc, which exports the /etc folder on the host container instance.

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    { "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.
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    "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 will likewise be mounted on the busybox container (including the volume specified in the Dockerfile that was used to build the my-repo/httpd_dockerfile_volume image).
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    { "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, which are then visible at the web site displayed by the web container.

    Note

    Because the busybox container runs a quick command and then exits, it needs to be set as "essential": false in the container definition to prevent it from stopping the entire task when it exits.