AWS Application Integration

These services connect applications and microservices through asynchronous messaging, event-driven architectures, and workflow orchestration.

Service Map

Service	Pattern	Use Case
SQS	Queue	Decouple producers/consumers, task queue
SNS	Pub/Sub	Fan-out to many subscribers
EventBridge	Event Bus	Schema registry, rules, SaaS ingestion
Step Functions	Workflow	Multi-step orchestration, long-running processes
Amazon MQ	Broker	ActiveMQ/RabbitMQ migration, JMS, protocol support
AppSync	GraphQL	Managed GraphQL API, real-time subscriptions

Choosing a Messaging Service

Need to send messages between services?
  │
  ├── One-to-one (point to point)
  │   └── SQS Queue — decouple, buffer, retry
  │
  ├── One-to-many (fan-out)
  │   ├── SNS Topic — push to many subscribers (SQS, HTTP, Lambda, etc.)
  │   └── EventBridge — rules-based routing, schema registry
  │
  ├── Event-driven (react to changes)
  │   └── EventBridge — rules, schedules, SaaS events
  │
  ├── Multi-step workflow
  │   └── Step Functions — state machines, human approval
  │
  └── Existing broker (migrating from ActiveMQ/RabbitMQ)
      └── Amazon MQ — managed ActiveMQ/RabbitMQ

References

• Homepage: https://aws.amazon.com/products/application-integration/
• Documentation: https://docs.aws.amazon.com/eventbridge/, https://docs.aws.amazon.com/sns/, etc.
• Pricing: https://aws.amazon.com/pricing/

Nuggets & Gotchas

• SQS doesn’t guarantee FIFO within a queue across multiple readers — use SQS FIFO queues if you need strict ordering: Standard SQS queues provide at-least-once delivery with no ordering guarantee. FIFO queues guarantee ordering but have a 300msg/s limit (vs unlimited for standard).
• SNS doesn’t persist messages — subscribers must be online when published: If a subscriber is offline (Lambda error, SQS queue temporarily empty), the message is NOT retried by SNS. Use SQS with SNS subscription (SQS queues persist messages) or EventBridge for retry logic.
• EventBridge’s default event bus only receives AWS events — for custom events, you create a custom event bus: The default event bus receives AWS service events. Custom applications publish to a custom event bus you create.
• Step Functions standard workflows have a 1-year execution limit — for longer workflows, use express workflows or redesign: Standard workflow executions can run up to 1 year. Express workflows have a 5-minute limit but handle 100K+ executions/second.
• Amazon MQ is NOT serverless — you pay for the broker instance 24/7: If you want managed messaging without fixed costs, use SQS/SNS (serverless, pay-per-request) instead of Amazon MQ.