AWS Step Functions

• Step Functions allow us to model our workflows as stat machines
• A workflow is represented as a JSON state machine
• Features:
  • Sequence
  • Parallel execution
  • Conditions
  • Timeouts
  • Error handling
• Can also integrate with EC2, ECS, on premise servers, API Gateway
• Maximum execution time is 1 year
• Possibility to implement human approval feature
• Use cases:
  • Order fulfillment
  • Data processing
  • Web applications
  • Any workflow
• When designing a Step Function we get an aspect of visualization (flow diagram)
• The execution can be visually represented on this diagram

Task States

• States in the state machine which can do some work, for example:
  • Invoke an AWS service such as Lambda function, start an AWS Batch job, run an ECS task, insert an item into DynamoDB table, etc.
  • Run an Activity:
    • Activities run on an EC2 machine, ECS container, on-premises server
    • Activities poll the Step Functions for work
    • Activities send back the result to the Step Function
• State types:
  • Choice State: test for a condition to send to a branch
  • Fail or Succeed State: stop execution with failure or success
  • Pass State: simply pass its input to the output or inject some fixed data
  • Wait State: wait for a certain amount of time or until a specific date/time
  • Map State: dynamically iterate steps
  • Parallel State: begin parallel branches of execution
• Any state can encounter errors:
  • State machine definition issues (example. no matching rules in choice state)
  • Task failures (example: an exception in a Lambda function)
  • Transient failures (example: network partition events)
• By default: when a state reports an error, the execution of the Step Functions fails entirely
• Failures can be retried:
  • Exponential back-off: IntervalSeconds, MaxAttempts, BackoffRate
  • Move on - Catch: ErrorEquals, Next
• Best practice: include data in the error message

Standard vs Express Step Functions

• Standard Function
  • Maximum duration: 1 year
  • Exactly-one workflow execution
  • Execution start rate: 2000 per second
  • Price per state transition: more expensive in general
• Express Function
  • Maximum duration: 5 minutes
  • At-least-once workflow execution, an execution could run more than once
  • Execution start rate: 100_000 per second

Step Function Use Cases

• Reference: https://aws.amazon.com/step-functions/use-cases/