AWS Step Functions Skill

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.

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

Agent Skills: AWS Step Functions

Skill Files