Step Functions

🔄 What is AWS Step Functions?

AWS Step Functions is a serverless orchestration service that lets you coordinate multiple AWS services (like Lambda, ECS, SQS, Glue) into stateful workflows using a JSON-based state machine.

✅ It visually represents each step, manages retries, catches failures, and maintains flow state.

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🎯 Why Use Step Functions?

Benefit	Description
✅ Visual workflows	Easy to understand and debug with the visual editor
🔁 Retry logic	Built-in error handling and retry strategies
🔄 State management	Maintains task output and passes it between steps
👷 Serverless orchestration	No need to write glue logic in code
🔐 IAM-secured	Permissions scoped per task (Lambda, SQS, ECS, etc.)

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🧠 Common Use Cases

Use Case	Description
🧾 Order Processing	Validate, charge, notify in sequence
🔄 ETL pipelines	Step-by-step data transformation (Glue, Lambda, Athena)
📦 Batch job control	Trigger and monitor ECS jobs or Batch tasks
✅ Approval workflows (manual + auto)	Wait for user input, branch based on approval
🔗 Chained Lambda execution	With branching, conditionals, error handling

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🔧 Types of Workflows

Type	Description	Use Case
Standard	Durable, long-running (up to 1 year)	ETL, approval flows
Express	High-speed, short-lived (up to 5 minutes)	Real-time event processing

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🧱 Basic Architecture

Start → Lambda → Choice → Parallel → Wait → Succeed/Fail

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📝 Sample State Machine (JSON)

{
  "Comment": "Sample Order Workflow",
  "StartAt": "ValidateOrder",
  "States": {
    "ValidateOrder": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:region:account-id:function:validateOrder",
      "Next": "ChargeCard"
    },
    "ChargeCard": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:region:account-id:function:chargeCard",
      "Catch": [{
        "ErrorEquals": ["States.ALL"],
        "Next": "NotifyFailure"
      }],
      "Next": "ShipOrder"
    },
    "ShipOrder": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:region:account-id:function:shipOrder",
      "End": true
    },
    "NotifyFailure": {
      "Type": "Fail",
      "Cause": "Charge failed"
    }
  }
}

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📦 Terraform Example (Standard Workflow + Lambda)

1. IAM Role for Step Function

resource "aws_iam_role" "step_fn_role" {
  name = "step_fn_role"
  assume_role_policy = jsonencode({
    Version = "2012-10-17",
    Statement = [{
      Effect = "Allow",
      Principal = {
        Service = "states.amazonaws.com"
      },
      Action = "sts:AssumeRole"
    }]
  })
}

resource "aws_iam_role_policy_attachment" "lambda_exec" {
  role       = aws_iam_role.step_fn_role.name
  policy_arn = "arn:aws:iam::aws:policy/AWSLambdaRole"
}

2. State Machine Definition

data "aws_lambda_function" "validate_order" {
  function_name = "validateOrder"
}

data "aws_lambda_function" "charge_card" {
  function_name = "chargeCard"
}

data "aws_lambda_function" "ship_order" {
  function_name = "shipOrder"
}

resource "aws_sfn_state_machine" "order_workflow" {
  name     = "order-processing"
  role_arn = aws_iam_role.step_fn_role.arn

  definition = jsonencode({
    StartAt = "ValidateOrder",
    States = {
      ValidateOrder = {
        Type     = "Task",
        Resource = data.aws_lambda_function.validate_order.arn,
        Next     = "ChargeCard"
      },
      ChargeCard = {
        Type     = "Task",
        Resource = data.aws_lambda_function.charge_card.arn,
        Next     = "ShipOrder"
      },
      ShipOrder = {
        Type     = "Task",
        Resource = data.aws_lambda_function.ship_order.arn,
        End      = true
      }
    }
  })
}

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🔐 Security & Permissions

Component	Required IAM Permissions
Step Function	states:StartExecution, states:Describe*
Lambda tasks	lambda:InvokeFunction
Other services	dynamodb:*, sqs:*, ecs:*, as needed

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📊 Monitoring

• CloudWatch Logs: Enable via workflow settings

• CloudWatch Metrics: Success, fail, duration, throttle, etc.

• X-Ray Tracing: Supported

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⚙️ Advanced Features

Feature	Description
🔄 Retry/Catch	Built-in error handling per state
⏱️ Wait	Add delays (seconds, timestamp, dynamic)
🧠 Choice	Conditional branching (like if/else)
⬛ Parallel	Run steps concurrently
📩 Map (for-each)	Loop over list of items
👤 Callback pattern	Wait for external system to send token (sync flow)
📥 Input/Output Path	Filter or transform data between steps

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💰 Pricing

Workflow Type	Pricing Detail
Standard	$0.025 per 1,000 state transitions
Express	$1.00 per million executions + duration-based compute fees

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✅ TL;DR Summary

Feature	AWS Step Functions
What is it?	Serverless workflow orchestrator
Types	Standard (durable) / Express (fast, high-volume)
Integrates with	Lambda, ECS, DynamoDB, Glue, SQS, SNS, etc.
Error handling	✅ Retry, Catch built-in
Visual flow editor	✅ Yes
Monitoring	CloudWatch, Logs, X-Ray
Terraform support	✅ Yes (aws_sfn_state_machine)

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