Serverless Patterns: Fan-Out, Choreography, and Orchestration

As serverless applications grow beyond single functions, you need architectural patterns to coordinate multiple services. This lesson covers three fundamental patterns — fan-out, choreography, and orchestration — along with practical implementations using AWS services.

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Why Patterns Matter

A single Lambda function responding to an API Gateway request is straightforward. But real-world applications require:

• Processing a single event in multiple ways simultaneously
• Coordinating multi-step workflows with error handling and retries
• Decoupling services so they can evolve independently
• Handling failures gracefully without losing data

The patterns in this lesson address these challenges.

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Pattern 1: Fan-Out

Fan-out distributes a single event to multiple consumers for parallel processing.

                    +---> Lambda A (resize image)
                    |
Event (S3 upload) --+--> Lambda B (extract metadata)
                    |
                    +---> Lambda C (virus scan)
                    |
                    +---> Lambda D (update database)

Implementation with SNS

SNS is the simplest fan-out mechanism — publish once, deliver to many:

# SAM Template
Resources:
  OrderTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: order-events

  SendConfirmationFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: src/sendConfirmation.handler
      Events:
        OrderPlaced:
          Type: SNS
          Properties:
            Topic: !Ref OrderTopic