Step Function –Task States

• Invoke one AWS service
  • Can invoke a Lambda function
  • Run an AWS Batch job
  • Run an ECS task and wait for it to complete
  • Insert an item from DynamoDB
  • Publish message to SNS, SQS
• Run an one Activity
  • EC2, Amazon ECS, on-premises
  • Activities poll the Step functions for work
  • Activities send results back to Step Functions

Step Function - States

• Choice State -Test for a condition to send to a branch (or default branch)
• Fail or Succeed State - Stop execution with failure or success
• Pass State - Simply pass its input to its output or inject some fixed data, without performing work.
• Wait State - Provide a delay for a certain amount of time or until a specified time/date.
• Map State - Dynamically iterate steps.
• Parallel State - Begin parallel branches of execution.

Error Handling in Step Functions

• Any state can encounter runtime errors for various reasons:
  • State machine definition issues (for example, no matching rule in a Choice state)
  • Task failures (for example, an exception in a Lambda function)
  • Transient issues (for example, network partition events)
• Use Retry (to retry failed state) and Catch (transition to failure path) in the State Machine to handle the errors instead of inside the Application Code
• Predefined error codes:
  • States.ALL : matches any error name
  • States.Timeout: Task ran longer than TimeoutSeconds or no heartbeat received
  • States.TaskFailed: execution failure
  • States.Permissions: insufficient privileges to execute code

Step Functions – Wait for Task Token

• Allows you to pause Step Functions during a Task until a Task Token is returned
• Task might wait for other AWS services, human approval, 3rd party integration, call legacy systems…
• Append .waitForTaskToken to the Resource field to tell Step Functions to wait for the Task Token to be returned
• Task will pause until it receives that Task Token back with a SendTaskSuccess or SendTaskFailure API call