How to orchestrate workflows with AWS Step Functions

AWS Step Functions coordinates multiple AWS services into serverless workflows defined as state machines. You describe states (Task, Choice, Parallel, Wait, Fail) in the Amazon States Language (JSON), and Step Functions handles execution, retries, and state tracking. It replaces brittle chains of Lambdas calling Lambdas.

Prerequisites

• An AWS account and Terraform.
• A few Lambda functions to orchestrate.

Steps

1. Model the workflow

Sketch the flow: validate an order, then in parallel charge payment and reserve stock, then either confirm or refund based on the result.

2. Write the state machine

State machines start with a StartAt and a States map:

{
  "StartAt": "Validate",
  "States": {
    "Validate": { "Type": "Task", "Resource": "<validate-arn>", "Next": "Charge" },
    "Charge": { "Type": "Task", "Resource": "<charge-arn>", "End": true }
  }
}

3. Add Task states

Each Task invokes a Lambda by ARN. Use ResultPath to merge a task's output into the running state instead of replacing it.

4. Add retries and catch

Make tasks resilient:

"Retry": [{ "ErrorEquals": ["States.TaskFailed"], "MaxAttempts": 3, "BackoffRate": 2 }],
"Catch": [{ "ErrorEquals": ["States.ALL"], "Next": "Refund" }]

Retries handle transient errors; catchers route persistent failures to a recovery state.

5. Branch with Choice

A Choice state inspects the state and routes accordingly:

"Decide": { "Type": "Choice", "Choices": [{ "Variable": "$.approved", "BooleanEquals": true, "Next": "Confirm" }], "Default": "Refund" }

6. Deploy and run

Deploy the definition with an aws_sfn_state_machine resource and an execution role allowing it to invoke the Lambdas, then start an execution:

aws stepfunctions start-execution --state-machine-arn <arn> --input '{"orderId":1}'

Verification

Open the execution in the Step Functions console and watch the visual graph color each state as it runs. Force a task to fail and confirm retries fire and the catcher routes to the recovery state. Confirm the Choice state branches as expected.

Next Steps

Use Express workflows for high-volume short executions, add a Map state to process arrays in parallel, and emit execution events to CloudWatch for alerting.