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AWS Data Pipeline
API Reference (API Version 2012-10-29)

PollForTask

Task runners call PollForTask to receive a task to perform from AWS Data Pipeline. The task runner specifies which tasks it can perform by setting a value for the workerGroup parameter. The task returned can come from any of the pipelines that match the workerGroup value passed in by the task runner and that was launched using the IAM user credentials specified by the task runner.

If tasks are ready in the work queue, PollForTask returns a response immediately. If no tasks are available in the queue, PollForTask uses long-polling and holds on to a poll connection for up to a 90 seconds, during which time the first newly scheduled task is handed to the task runner. To accomodate this, set the socket timeout in your task runner to 90 seconds. The task runner should not call PollForTask again on the same workerGroup until it receives a response, and this can take up to 90 seconds.

Request Syntax

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{ "hostname": "string", "instanceIdentity": { "document": "string", "signature": "string" }, "workerGroup": "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.

hostname

The public DNS name of the calling task runner.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 1024.

Pattern: [\u0020-\uD7FF\uE000-\uFFFD\uD800\uDC00-\uDBFF\uDFFF\n\t]*

Required: No

instanceIdentity

Identity information for the EC2 instance that is hosting the task runner. You can get this value from the instance using http://169.254.169.254/latest/meta-data/instance-id. For more information, see Instance Metadata in the Amazon Elastic Compute Cloud User Guide. Passing in this value proves that your task runner is running on an EC2 instance, and ensures the proper AWS Data Pipeline service charges are applied to your pipeline.

Type: InstanceIdentity object

Required: No

workerGroup

The type of task the task runner is configured to accept and process. The worker group is set as a field on objects in the pipeline when they are created. You can only specify a single value for workerGroup in the call to PollForTask. There are no wildcard values permitted in workerGroup; the string must be an exact, case-sensitive, match.

Type: String

Required: Yes

Response Syntax

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{ "taskObject": { "attemptId": "string", "objects": { "string" : { "fields": [ { "key": "string", "refValue": "string", "stringValue": "string" } ], "id": "string", "name": "string" } }, "pipelineId": "string", "taskId": "string" } }

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.

taskObject

The information needed to complete the task that is being assigned to the task runner. One of the fields returned in this object is taskId, which contains an identifier for the task being assigned. The calling task runner uses taskId in subsequent calls to ReportTaskProgress and SetTaskStatus.

Type: TaskObject object

Errors

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

InternalServiceError

An internal service error occurred.

HTTP Status Code: 500

InvalidRequestException

The request was not valid. Verify that your request was properly formatted, that the signature was generated with the correct credentials, and that you haven't exceeded any of the service limits for your account.

HTTP Status Code: 400

TaskNotFoundException

The specified task was not found.

HTTP Status Code: 400

Example

Sample Request

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POST / HTTP/1.1 Content-Type: application/x-amz-json-1.1 X-Amz-Target: DataPipeline.PollForTask Content-Length: 59 Host: datapipeline.us-east-1.amazonaws.com X-Amz-Date: Mon, 12 Nov 2012 17:49:52 GMT Authorization: AuthParams {"workerGroup": "MyworkerGroup", "hostname": "example.com"}

Sample Response

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x-amzn-RequestId: 41c713d2-0775-11e2-af6f-6bc7a6be60d9 Content-Type: application/x-amz-json-1.1 Content-Length: 39 Date: Mon, 12 Nov 2012 17:50:53 GMT {"taskObject": {"attemptId": "@SayHello_2012-12-12T00:00:00_Attempt=1", "objects": {"@SayHello_2012-12-12T00:00:00_Attempt=1": {"fields": [ {"key": "@componentParent", "refValue": "SayHello"}, {"key": "@scheduledStartTime", "stringValue": "2012-12-12T00:00:00"}, {"key": "parent", "refValue": "SayHello"}, {"key": "@sphere", "stringValue": "ATTEMPT"}, {"key": "workerGroup", "stringValue": "workerGroup"}, {"key": "@instanceParent", "refValue": "@SayHello_2012-12-12T00:00:00"}, {"key": "type", "stringValue": "ShellCommandActivity"}, {"key": "@status", "stringValue": "WAITING_FOR_RUNNER"}, {"key": "@version", "stringValue": "1"}, {"key": "schedule", "refValue": "Schedule"}, {"key": "@actualStartTime", "stringValue": "2012-12-13T01:40:50"}, {"key": "command", "stringValue": "echo hello"}, {"key": "@scheduledEndTime", "stringValue": "2012-12-12T01:00:00"}, {"key": "@activeInstances", "refValue": "@SayHello_2012-12-12T00:00:00"}, {"key": "@pipelineId", "stringValue": "df-0937003356ZJEXAMPLE"} ], "id": "@SayHello_2012-12-12T00:00:00_Attempt=1", "name": "@SayHello_2012-12-12T00:00:00_Attempt=1"} }, "pipelineId": "df-0937003356ZJEXAMPLE", "taskId": "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:XO50TgDNyo8EXAMPLE/g==:1"} }

See Also

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