step-functions

AWS Step Functions

AWS Step Functions is a serverless orchestration service that lets you build and run workflows using state machines. Coordinate multiple AWS services into business-critical applications.

Table of Contents

• Core Concepts
• Common Patterns
• CLI Reference
• Best Practices
• Troubleshooting
• References

Core Concepts

Workflow Types

Type	Description	Pricing
Standard	Long-running, durable, exactly-once	Per state transition
Express	High-volume, short-duration	Per execution (time + memory)

State Types

State	Description
Task	Execute work (Lambda, API call)
Choice	Conditional branching
Parallel	Execute branches concurrently
Map	Iterate over array
Wait	Delay execution
Pass	Pass input to output
Succeed	End successfully
Fail	End with failure

Amazon States Language (ASL)

JSON-based language for defining state machines.

Common Patterns

Simple Lambda Workflow

{
  "Comment": "Process order workflow",
  "StartAt": "ValidateOrder",
  "States": {
    "ValidateOrder": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:us-east-1:123456789012:function:ValidateOrder",
      "Next": "ProcessPayment"
    },
    "ProcessPayment": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:us-east-1:123456789012:function:ProcessPayment",
      "Next": "FulfillOrder"
    },
    "FulfillOrder": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:us-east-1:123456789012:function:FulfillOrder",
      "End": true
    }
  }
}

Create State Machine

AWS CLI:

aws stepfunctions create-state-machine \
  --name OrderWorkflow \
  --definition file://workflow.json \
  --role-arn arn:aws:iam::123456789012:role/StepFunctionsRole \
  --type STANDARD

boto3:

import boto3
import json

sfn = boto3.client('stepfunctions')

definition = {
    "Comment": "Order workflow",
    "StartAt": "ProcessOrder",
    "States": {
        "ProcessOrder": {
            "Type": "Task",
            "Resource": "arn:aws:lambda:...",
            "End": True
        }
    }
}

response = sfn.create_state_machine(
    name='OrderWorkflow',
    definition=json.dumps(definition),
    roleArn='arn:aws:iam::123456789012:role/StepFunctionsRole',
    type='STANDARD'
)

Start Execution

import boto3
import json

sfn = boto3.client('stepfunctions')

response = sfn.start_execution(
    stateMachineArn='arn:aws:states:us-east-1:123456789012:stateMachine:OrderWorkflow',
    name='order-12345',
    input=json.dumps({
        'order_id': '12345',
        'customer_id': 'cust-789',
        'items': [{'product_id': 'prod-1', 'quantity': 2}]
    })
)

execution_arn = response['executionArn']

Choice State (Conditional Logic)

{
  "StartAt": "CheckOrderValue",
  "States": {
    "CheckOrderValue": {
      "Type": "Choice",
      "Choices": [
        {
          "Variable": "$.total",
          "NumericGreaterThan": 1000,
          "Next": "HighValueOrder"
        },
        {
          "Variable": "$.priority",
          "StringEquals": "rush",
          "Next": "RushOrder"
        }
      ],
      "Default": "StandardOrder"
    },
    "HighValueOrder": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:...:function:ProcessHighValue",
      "End": true
    },
    "RushOrder": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:...:function:ProcessRush",
      "End": true
    },
    "StandardOrder": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:...:function:ProcessStandard",
      "End": true
    }
  }
}

Parallel Execution

{
  "StartAt": "ProcessInParallel",
  "States": {
    "ProcessInParallel": {
      "Type": "Parallel",
      "Branches": [
        {
          "StartAt": "UpdateInventory",
          "States": {
            "UpdateInventory": {
              "Type": "Task",
              "Resource": "arn:aws:lambda:...:function:UpdateInventory",
              "End": true
            }
          }
        },
        {
          "StartAt": "SendNotification",
          "States": {
            "SendNotification": {
              "Type": "Task",
              "Resource": "arn:aws:lambda:...:function:SendNotification",
              "End": true
            }
          }
        },
        {
          "StartAt": "UpdateAnalytics",
          "States": {
            "UpdateAnalytics": {
              "Type": "Task",
              "Resource": "arn:aws:lambda:...:function:UpdateAnalytics",
              "End": true
            }
          }
        }
      ],
      "Next": "Complete"
    },
    "Complete": {
      "Type": "Succeed"
    }
  }
}

Map State (Iteration)

{
  "StartAt": "ProcessItems",
  "States": {
    "ProcessItems": {
      "Type": "Map",
      "ItemsPath": "$.items",
      "MaxConcurrency": 10,
      "Iterator": {
        "StartAt": "ProcessItem",
        "States": {
          "ProcessItem": {
            "Type": "Task",
            "Resource": "arn:aws:lambda:...:function:ProcessItem",
            "End": true
          }
        }
      },
      "ResultPath": "$.processedItems",
      "End": true
    }
  }
}

Error Handling

{
  "StartAt": "ProcessWithRetry",
  "States": {
    "ProcessWithRetry": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:...:function:Process",
      "Retry": [
        {
          "ErrorEquals": ["Lambda.ServiceException", "Lambda.TooManyRequestsException"],
          "IntervalSeconds": 2,
          "MaxAttempts": 6,
          "BackoffRate": 2
        },
        {
          "ErrorEquals": ["States.Timeout"],
          "IntervalSeconds": 5,
          "MaxAttempts": 3,
          "BackoffRate": 1.5
        }
      ],
      "Catch": [
        {
          "ErrorEquals": ["CustomError"],
          "ResultPath": "$.error",
          "Next": "HandleCustomError"
        },
        {
          "ErrorEquals": ["States.ALL"],
          "ResultPath": "$.error",
          "Next": "HandleAllErrors"
        }
      ],
      "End": true
    },
    "HandleCustomError": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:...:function:HandleCustom",
      "End": true
    },
    "HandleAllErrors": {
      "Type": "Fail",
      "Error": "ProcessingFailed",
      "Cause": "An error occurred during processing"
    }
  }
}

CLI Reference

State Machine Management

Command	Description
aws stepfunctions create-state-machine	Create state machine
aws stepfunctions update-state-machine	Update definition
aws stepfunctions delete-state-machine	Delete state machine
aws stepfunctions list-state-machines	List state machines
aws stepfunctions describe-state-machine	Get details

Executions

Command	Description
aws stepfunctions start-execution	Start execution
aws stepfunctions stop-execution	Stop execution
aws stepfunctions describe-execution	Get execution details
aws stepfunctions list-executions	List executions
aws stepfunctions get-execution-history	Get execution history

Best Practices

Design

• Keep states focused — one purpose per state
• Use meaningful state names
• Implement comprehensive error handling
• Use Parallel for independent tasks
• Use Map for batch processing

Performance

• Use Express workflows for high-volume, short tasks
• Set appropriate timeouts
• Limit Map concurrency to avoid throttling
• Use SDK integrations when possible (avoid Lambda wrapper)

Reliability

• Retry transient errors
• Catch and handle specific errors
• Use idempotent operations
• Enable X-Ray tracing

Cost Optimization

• Use Express for short workflows (< 5 minutes)
• Combine related operations to reduce transitions
• Use Wait states instead of Lambda delays

Troubleshooting

Execution Failed

# Get execution history
aws stepfunctions get-execution-history \
  --execution-arn arn:aws:states:us-east-1:123456789012:execution:MyWorkflow:exec-123 \
  --query 'events[?type==`TaskFailed` || type==`ExecutionFailed`]'

Lambda Timeout

Causes:

• Lambda running too long
• Task timeout too short

Fix:

{
  "Type": "Task",
  "Resource": "arn:aws:lambda:...",
  "TimeoutSeconds": 300,
  "HeartbeatSeconds": 60
}

State Stuck

Check:

• Task state waiting for callback
• Wait state not yet elapsed
• Activity worker not responding

Invalid State Machine

# Validate definition
aws stepfunctions validate-state-machine-definition \
  --definition file://workflow.json

References

• Step Functions Developer Guide
• Step Functions API Reference
• Step Functions CLI Reference
• Amazon States Language