AWS Step Functions: Workflow Orchestration

While SQS, SNS, and EventBridge excel at decoupled, event-driven communication, some workflows require coordination — steps that must happen in a specific sequence, with branching logic, error handling, and retries. AWS Step Functions is a serverless workflow orchestration service that lets you coordinate multiple AWS services into structured, visual workflows.

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Choreography vs Orchestration

Event-driven systems use two coordination styles:

Choreography (Decentralised)

Each service reacts to events independently. There is no central coordinator — services communicate through events.

[Order Service] ——event——> [Payment Service] ——event——> [Shipping Service]

Pros: Loose coupling, each service is independent. Cons: Hard to see the full workflow, difficult to handle failures across services.

Orchestration (Centralised)

A central coordinator (Step Functions) manages the workflow. It calls each service in the right order, handles errors, and tracks state.

[Step Functions Orchestrator]
     |——> Step 1: Validate Order
     |——> Step 2: Process Payment
     |——> Step 3: Reserve Inventory
     |——> Step 4: Ship Order
     |——> Step 5: Send Confirmation

Pros: Clear visibility, centralised error handling, easy to modify workflow. Cons: Central coordinator introduces a dependency.