Integration, Events, and Workflow Selection

What This Chapter Is About

Teach integration as choosing the right communication contract between systems: synchronous request, queue, pub/sub event, routed event, workflow, or processor.

Keep one durable idea in view:

Integration design is about the promise one system makes to another.

Sections

1. Integration Contract Mental Model

2. APIs, Queues, Topics, Events, and Workflows

3. Reliability Patterns for Event-Driven Systems

4. Order Processing Integration Scenario

5. Choosing Communication Patterns in Architecture Conversations

How the Chapter Develops

The chapter develops in this order:

1. Start with communication intent and contract shape.

2. Compare API Gateway, SQS, SNS, EventBridge, Step Functions, Lambda, and containers by responsibility.

3. Add reliability concerns: idempotency, retries, dead-letter queues, ordering, replay, schema evolution, and observability.

4. Apply the model to order processing with payment, inventory, fulfillment, and partner notification.

5. Prepare a conversation-ready answer that explains trade-offs clearly.

What You Will Be Able to Do

By the end of this chapter, the reader should be able to:

• Explain when systems should communicate synchronously and when they should decouple.

• Compare SQS, SNS, EventBridge, and Step Functions by communication intent.

• Identify reliability controls needed for event-driven architecture.

• Design a practical integration model for order processing.

Key Ideas

• Synchronous APIs are useful for immediate answers but couple availability and latency.

• Queues protect producers and consumers from moving at the same speed.

• Events help systems react without requiring the producer to know every consumer.

• Workflows coordinate multi-step processes when state, retries, and branching matter.