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


Starts a new task using the specified task definition.

You can allow Amazon ECS to place tasks for you, or you can customize how Amazon ECS places tasks using placement constraints and placement strategies. For more information, see Scheduling Tasks in the Amazon Elastic Container Service Developer Guide.

Alternatively, you can use StartTask to use your own scheduler or place tasks manually on specific container instances.

The Amazon ECS API follows an eventual consistency model, due to the distributed nature of the system supporting the API. This means that the result of an API command you run that affects your Amazon ECS resources might not be immediately visible to all subsequent commands you run. You should keep this in mind when you carry out an API command that immediately follows a previous API command.

To manage eventual consistency, you can do the following:

  • Confirm the state of the resource before you run a command to modify it. Run the DescribeTasks command using an exponential backoff algorithm to ensure that you allow enough time for the previous command to propagate through the system. To do this, run the DescribeTasks command repeatedly, starting with a couple of seconds of wait time, and increasing gradually up to five minutes of wait time.

  • Add wait time between subsequent commands, even if the DescribeTasks command returns an accurate response. Apply an exponential backoff algorithm starting with a couple of seconds of wait time, and increase gradually up to about five minutes of wait time.

Request Syntax

{ "cluster": "string", "count": number, "group": "string", "launchType": "string", "networkConfiguration": { "awsvpcConfiguration": { "assignPublicIp": "string", "securityGroups": [ "string" ], "subnets": [ "string" ] } }, "overrides": { "containerOverrides": [ { "command": [ "string" ], "cpu": number, "environment": [ { "name": "string", "value": "string" } ], "memory": number, "memoryReservation": number, "name": "string" } ], "executionRoleArn": "string", "taskRoleArn": "string" }, "placementConstraints": [ { "expression": "string", "type": "string" } ], "placementStrategy": [ { "field": "string", "type": "string" } ], "platformVersion": "string", "startedBy": "string", "taskDefinition": "string" }

Request Parameters

For information about the parameters that are common to all actions, see Common Parameters.

The request accepts the following data in JSON format.


The short name or full Amazon Resource Name (ARN) of the cluster on which to run your task. If you do not specify a cluster, the default cluster is assumed.

Type: String

Required: No


The number of instantiations of the specified task to place on your cluster. You can specify up to 10 tasks per call.

Type: Integer

Required: No


The name of the task group to associate with the task. The default value is the family name of the task definition (for example, family:my-family-name).

Type: String

Required: No


The launch type on which to run your task.

Type: String

Valid Values: EC2 | FARGATE

Required: No


The network configuration for the task. This parameter is required for task definitions that use the awsvpc network mode to receive their own Elastic Network Interface, and it is not supported for other network modes. For more information, see Task Networking in the Amazon Elastic Container Service Developer Guide.

Type: NetworkConfiguration object

Required: No


A list of container overrides in JSON format that specify the name of a container in the specified task definition and the overrides it should receive. You can override the default command for a container (that is specified in the task definition or Docker image) with a command override. You can also override existing environment variables (that are specified in the task definition or Docker image) on a container or add new environment variables to it with an environment override.


A total of 8192 characters are allowed for overrides. This limit includes the JSON formatting characters of the override structure.

Type: TaskOverride object

Required: No


An array of placement constraint objects to use for the task. You can specify up to 10 constraints per task (including constraints in the task definition and those specified at run time).

Type: Array of PlacementConstraint objects

Required: No


The placement strategy objects to use for the task. You can specify a maximum of five strategy rules per task.

Type: Array of PlacementStrategy objects

Required: No


The platform version on which to run your task. If one is not specified, the latest version is used by default.

Type: String

Required: No


An optional tag specified when a task is started. For example if you automatically trigger a task to run a batch process job, you could apply a unique identifier for that job to your task with the startedBy parameter. You can then identify which tasks belong to that job by filtering the results of a ListTasks call with the startedBy value. Up to 36 letters (uppercase and lowercase), numbers, hyphens, and underscores are allowed.

If a task is started by an Amazon ECS service, then the startedBy parameter contains the deployment ID of the service that starts it.

Type: String

Required: No


The family and revision (family:revision) or full ARN of the task definition to run. If a revision is not specified, the latest ACTIVE revision is used.

Type: String

Required: Yes

Response Syntax

{ "failures": [ { "arn": "string", "reason": "string" } ], "tasks": [ { "attachments": [ { "details": [ { "name": "string", "value": "string" } ], "id": "string", "status": "string", "type": "string" } ], "clusterArn": "string", "connectivity": "string", "connectivityAt": number, "containerInstanceArn": "string", "containers": [ { "containerArn": "string", "exitCode": number, "lastStatus": "string", "name": "string", "networkBindings": [ { "bindIP": "string", "containerPort": number, "hostPort": number, "protocol": "string" } ], "networkInterfaces": [ { "attachmentId": "string", "ipv6Address": "string", "privateIpv4Address": "string" } ], "reason": "string", "taskArn": "string" } ], "cpu": "string", "createdAt": number, "desiredStatus": "string", "executionStoppedAt": number, "group": "string", "lastStatus": "string", "launchType": "string", "memory": "string", "overrides": { "containerOverrides": [ { "command": [ "string" ], "cpu": number, "environment": [ { "name": "string", "value": "string" } ], "memory": number, "memoryReservation": number, "name": "string" } ], "executionRoleArn": "string", "taskRoleArn": "string" }, "platformVersion": "string", "pullStartedAt": number, "pullStoppedAt": number, "startedAt": number, "startedBy": "string", "stoppedAt": number, "stoppedReason": "string", "stoppingAt": number, "taskArn": "string", "taskDefinitionArn": "string", "version": number } ] }

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.


Any failures associated with the call.

Type: Array of Failure objects


A full description of the tasks that were run. The tasks that were successfully placed on your cluster are described here.

Type: Array of Task objects


For information about the errors that are common to all actions, see Common Errors.


You do not have authorization to perform the requested action.

HTTP Status Code: 400


Your AWS account has been blocked. Contact AWS Customer Support for more information.

HTTP Status Code: 400


These errors are usually caused by a client action, such as using an action or resource on behalf of a user that doesn't have permissions to use the action or resource, or specifying an identifier that is not valid.

HTTP Status Code: 400


The specified cluster could not be found. You can view your available clusters with ListClusters. Amazon ECS clusters are region-specific.

HTTP Status Code: 400


The specified parameter is invalid. Review the available parameters for the API request.

HTTP Status Code: 400


The specified platform version does not satisfy the task definition’s required capabilities.

HTTP Status Code: 400


The specified platform version does not exist.

HTTP Status Code: 400


These errors are usually caused by a server issue.

HTTP Status Code: 500


The specified task is not supported in this region.

HTTP Status Code: 400


In the following example or examples, the Authorization header contents (AUTHPARAMS) must be replaced with an AWS Signature Version 4 signature. For more information, see Signature Version 4 Signing Process in the AWS General Reference.

You only need to learn how to sign HTTP requests if you intend to create them manually. When you use the AWS Command Line Interface (AWS CLI) or one of the AWS SDKs to make requests to AWS, these tools automatically sign the requests for you, with the access key that you specify when you configure the tools. When you use these tools, you don't have to sign requests yourself.


This example request runs the latest ACTIVE revision of the hello_world task definition family in the default cluster.

Sample Request

POST / HTTP/1.1 Host: Accept-Encoding: identity Content-Length: 45 X-Amz-Target: AmazonEC2ContainerServiceV20141113.RunTask X-Amz-Date: 20161121T215740Z User-Agent: aws-cli/1.11.13 Python/2.7.12 Darwin/16.1.0 botocore/1.4.66 Content-Type: application/x-amz-json-1.1 Authorization: AUTHPARAMS { "count": 1, "taskDefinition": "hello_world" }

Sample Response

HTTP/1.1 200 OK Server: Server Date: Mon, 21 Nov 2016 21:57:40 GMT Content-Type: application/x-amz-json-1.1 Content-Length: 1025 Connection: keep-alive x-amzn-RequestId: 123a4b56-7c89-01d2-3ef4-example5678f { "failures": [], "tasks": [ { "clusterArn": "arn:aws:ecs:us-east-1:012345678910:cluster/default", "containerInstanceArn": "arn:aws:ecs:us-east-1:012345678910:container-instance/4c543eed-f83f-47da-b1d8-3d23f1da4c64", "containers": [ { "containerArn": "arn:aws:ecs:us-east-1:012345678910:container/e76594d4-27e1-4c74-98b5-46a6435eb769", "lastStatus": "PENDING", "name": "wordpress", "taskArn": "arn:aws:ecs:us-east-1:012345678910:task/fdf2c302-468c-4e55-b884-5331d816e7fb" }, { "containerArn": "arn:aws:ecs:us-east-1:012345678910:container/b19106ea-4fa8-4f1d-9767-96922c82b070", "lastStatus": "PENDING", "name": "mysql", "taskArn": "arn:aws:ecs:us-east-1:012345678910:task/fdf2c302-468c-4e55-b884-5331d816e7fb" } ], "createdAt": 1479765460.842, "desiredStatus": "RUNNING", "lastStatus": "PENDING", "overrides": { "containerOverrides": [ { "name": "wordpress" }, { "name": "mysql" } ] }, "taskArn": "arn:aws:ecs:us-east-1:012345678910:task/fdf2c302-468c-4e55-b884-5331d816e7fb", "taskDefinitionArn": "arn:aws:ecs:us-east-1:012345678910:task-definition/hello_world:6", "version": 1 } ] }

See Also

For more information about using this API in one of the language-specific AWS SDKs, see the following: