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Amazon Simple Workflow Service
Developer Guide (API Version 2012-01-25)

Amazon Simple Workflow Service Limits

Amazon SWF places limits on the sizes of certain workflow parameters, such as on the number of domains per account and on the size of the workflow execution history. These limits are designed to prevent erroneous workflows from consuming all of the resources of the system, but are not hard limits. If you find that your application is frequently exceeding these limits, you can request a service limit increase.

General Account Limits for Amazon SWF

  • Maximum registered domains – 100

    This limit includes both registered and deprecated domains.

  • Maximum workflow and activity types – 10,000 each per domain

    This limit includes both registered and deprecated types.

  • API call limit – Beyond infrequent spikes, applications may be throttled if they make a large number of API calls in a very short period of time.

  • Maximum request size – 1 MB per request

    This is the total data size per Amazon SWF API request, including the request header and all other associated request data.

Limits on Workflow Executions

  • Maximum open workflow executions – 100,000 per domain

    This count includes child workflow executions.

  • Maximum workflow execution time – 1 year

  • Maximum workflow execution history size – 25,000 events

  • Maximum child workflow executions – 1,000 per workflow execution.

  • Workflow execution idle time limit – 1 year (constrained by workflow execution time limit)

    You can configure workflow timeouts to cause a timeout event to occur if a particular stage of your workflow takes too long.

  • Workflow retention time limit – 90 days

    After this time, the workflow history can no longer be retrieved or viewed. There is no further limit to the number of closed workflow executions that are retained by Amazon SWF.

If your use case requires you to go beyond these limits, you can use features Amazon SWF provides to continue executions and structure your applications using child workflow executions. If you find that you still need a limits increase, see Requesting a Limit Increase.

Limits on Task Executions

  • Maximum pollers per task list – 100 per host, per tasklist

    There are 10 hosts available, so the limit of pollers per task list is 1000 total. However, if a single host receives 101 pollers on a particular task list, a LimitExceededException will result.

  • Maximum task execution time – 1 year (constrained by workflow execution time limit)

    You can configure activity timeouts to cause a timeout event to occur if a particular stage of your activity task execution takes too long.

  • Maximum time SWF will keep a task in the queue – 1 year (constrained by workflow execution time limit)

    You can configure default activity timeouts during activity registration that will cause a timeout event to occur if a particular stage of your activity task execution takes too long. You can also override the default activity timeouts when you schedule an activity task in your decider code.

  • Maximum open activity tasks – 1,000 per workflow execution.

    This limit includes both activity tasks that have been scheduled and those being processed by workers.

  • Maximum open timers – 1,000 per workflow execution

  • Maximum input/result data size – 32,000 characters

    This limit affects activity or workflow execution result data, input data when scheduling activity tasks or workflow executions, and input sent with a workflow execution signal.

  • Maximum decisions in a decision task response – varies

    Due to the 1 MB limit on the maximum API request size, the number of decisions returned in a single call to RespondDecisionTaskCompleted will be limited according to the size of the data used by each decision, including the size of any input data provided to scheduled activity tasks or to workflow executions.

Amazon SWF throttling limits

In addition to the service limits described previously, certain Amazon SWF API calls and decision events are throttled to maintain service bandwidth, using a token bucket scheme. If your rate of requests consistently exceeds the rates that are listed here, you can request a throttle limit increase.

Throttling limits are per account / region. Limits in us-east-1 are slightly different than in other regions; refer to the section that corresponds to your region:

Throttling limits for us-east-1

API limits

API nameBucket sizeRefill rate / s
CountClosedWorkflowExecutions10001
CountOpenWorkflowExecutions10001
CountPendingActivityTasks1001
CountPendingDecisionTasks1001
DeprecateActivityType1001
DeprecateDomain501
DeprecateWorkflowType1001
DescribeActivityType10001
DescribeDomain1001
DescribeWorkflowExecution10001
DescribeWorkflowType10001
GetWorkflowExecutionHistory10005
ListActivityTypes1001
ListClosedWorkflowExecutions1001
ListDomains501
ListOpenWorkflowExecutions1001
ListWorkflowTypes1001
PollForActivityTask1000100
PollForDecisionTask1000142
RecordActivityTaskHeartbeat10001
RegisterActivityType1001
RegisterDomain501
RegisterWorkflowType1001
RequestCancelWorkflowExecution10005
RespondActivityTaskCanceled1000100
RespondActivityTaskCompleted1000100
RespondActivityTaskFailed1000100
RespondDecisionTaskCompleted1000142
SignalWorkflowExecution10005
StartWorkflowExecution100025
TerminateWorkflowExecution100010

Decision limits

DecisionBucket sizeRefill rate / s
RequestCancelExternalWorkflowExecution10010
ScheduleActivityTask500100
SignalExternalWorkflowExecution10010
StartChildWorkflowExecution5002
StartTimer1000142

Throttling limits for other regions

API limits

API nameBucket sizeRefill rate / s
CountClosedWorkflowExecutions10001
CountOpenWorkflowExecutions10001
CountPendingActivityTasks1001
CountPendingDecisionTasks1001
DeprecateActivityType1001
DeprecateDomain501
DeprecateWorkflowType1001
DescribeActivityType10001
DescribeDomain1001
DescribeWorkflowExecution10001
DescribeWorkflowType10001
GetWorkflowExecutionHistory10005
ListActivityTypes1001
ListClosedWorkflowExecutions1001
ListDomains501
ListOpenWorkflowExecutions1001
ListWorkflowTypes1001
PollForActivityTask100010
PollForDecisionTask100012
RecordActivityTaskHeartbeat10001
RegisterActivityType1001
RegisterDomain501
RegisterWorkflowType1001
RequestCancelWorkflowExecution10005
RespondActivityTaskCanceled100010
RespondActivityTaskCompleted100010
RespondActivityTaskFailed100010
RespondDecisionTaskCompleted100012
SignalWorkflowExecution10005
StartWorkflowExecution10002
TerminateWorkflowExecution100010

Decision limits

DecisionBucket sizeRefill rate / s
RequestCancelExternalWorkflowExecution10010
ScheduleActivityTask10010
SignalExternalWorkflowExecution10010
StartChildWorkflowExecution1002
StartTimer50025

Requesting a Limit Increase

Use the Support Center page in the AWS Management Console to request a limit increase for resources provided by AWS Step Functions on a per-region basis. For more information, see To Request a Limit Increase in the AWS General Reference.