Step Functions

AWS Step Functions are a serverless orchestration service designed for event-driven task execution, enabling the combination of various AWS services for business applications.

AWS Step Functions has two main types of workflows:

1. Standard Workflows:

• Can run for up to 1 year

• Best for long-running, auditable workflows

• Follows exactly-once execution model

• Higher pricing

• Useful for orchestrating human approval workflows

• Good for business process workflows

1. Express Workflows:

Split into two subtypes:

Synchronous Express:

• Run up to 5 minutes

• Returns result after workflow completes

• Good for request-response patterns

• Real-time processing scenarios

Asynchronous Express:

• Run up to 5 minutes

• Doesn't wait for workflow completion

• Better for high-volume event processing

• Fire-and-forget scenarios

• Message processing use cases

The main differences between Standard and Express are:

• Execution time limits (1 year vs 5 minutes)

• Execution model (exactly-once vs at-least-once)

• Pricing (Standard costs more per state transition)

• Execution tracking (Standard provides full audit history)

Choose Standard when you need long-running workflows with full history and exactly-once execution. Choose Express when you need high-volume, short-lived workflows where at-least-once execution is acceptable.

Core Components

State Machines

• Represents a workflow with different event-driven steps

• Uses Amazon States Language

• Includes a graphical console and workflow viewer

• Each workflow can have multiple executions (instances of running workflows)

States (Steps)

• Represent individual units of work within a workflow

• Each state is referenced by a unique name

• Can make decisions based on input, perform actions, or pass output

Workflow Types

Feature	Standard Workflows	Express Workflows (Async)	Express Workflows (Sync)
Execution Guarantee	Exactly-once execution	At-least-once execution	At-least-once execution
Duration Limit	Up to 1 year	Up to 5 minutes	Up to 30 seconds
Best Used For	Long-running workflows requiring audit history	High-volume event processing with eventual consistency	High-volume API orchestration needing immediate response
Performance	Up to 2,000 executions/second	Up to 100,000 executions/second	Up to 100,000 executions/second
Use Case Example	Complex business processes	IoT data streaming and ingestion	Real-time transaction processing
Pricing Model	Per state transition	Based on executions, duration, and memory	Based on executions, duration, and memory
Response Type	Asynchronous	Asynchronous	Synchronous (waits for workflow completion)

The key difference between Async and Sync Express workflows is that synchronous executions wait for the workflow to complete and return the result, while asynchronous executions start the workflow but don't wait for completion. Sync Express workflows also have a shorter duration limit of 30 seconds compared to 5 minutes for async Express workflows.

State Types

1. Pass State

   • Passes input directly to output

2. Task State

   • Performs a single unit of work

   • Can integrate with services like Lambda, Batch, and SNS

3. Choice State

   • Adds branching logic to the state machine

4. Wait State

   • Creates specific time delays

5. Succeed State

   • Stops execution successfully

6. Fail State

   • Stops execution and marks as failed

7. Parallel State

   • Executes multiple branches simultaneously

8. Map State

   • Runs steps based on elements of an input array

Real-World Example

An online pickup order workflow where each step in the process represents a different state in the state machine.