How to asynchronously decouple a SaaS application feeding updates to other applications?
1. Amazon SQS (Simple Queue Service)
- Use case: Decouples components by sending messages to a queue.
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Limitation for this case:
- SQS is a point-to-point queue system. Each message is consumed by only one consumer.
- If you have multiple applications (in-house + third-party) that all need to receive the same updates, SQS won’t broadcast to all — it only delivers to one consumer per message.
- You’d need extra complexity (fan-out architecture) to handle multiple consumers.
⚡ Conclusion: SQS is not ideal if updates must go to multiple consumers directly.
2. Amazon SNS (Simple Notification Service)
- Use case: Pub/sub model — good for broadcasting messages to multiple subscribers.
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Limitation for this case:
- SNS is great for simple push notifications to multiple endpoints.
- But if the SaaS application sends updates to in-house and third-party apps and those third-party apps may not support SNS subscription protocols (HTTP/S, email, SMS, Lambda), SNS becomes harder to manage.
- SNS has no built-in persistence beyond a short retry policy (minutes).
- If consumers are offline, they may miss updates unless paired with SQS (SNS → SQS pattern).
- SaaS → SNS integration often requires more setup and protocol handling.
⚡ Conclusion: SNS alone doesn’t guarantee reliable delivery if consumers are temporarily offline or need message persistence.
Better option for this use case
For asynchronous decoupling where:
- multiple consumers exist,
- updates are critical,
- some consumers may be offline or third-party,
Amazon EventBridge is the best choice.
Why EventBridge?
- Supports event-driven architecture.
- Allows multiple targets (in-house apps, third-party SaaS apps, Lambda, Step Functions, etc.).
- Has event buses to route events based on rules.
- Can handle schema validation for SaaS events.
- Supports SaaS integrations via partner event sources.
- Can persist events for up to 24 hours if needed.
✅ This makes EventBridge ideal for a SaaS application feeding updates to multiple consumers asynchronously without tight coupling.
Summary Table:
| Service | Pros | Cons |
|---|---|---|
| SQS | Durable queue, message persistence | Single consumer per message, needs extra complexity for fan-out |
| SNS | Pub/Sub to multiple endpoints | No persistence, consumers must be active, protocol limitations |
| EventBridge | Pub/Sub with rules, persistence, SaaS integrations | More setup complexity than SNS/SQS |
💡 In short:
- SQS = single consumer, not direct fan-out.
- SNS = pub/sub, but no persistence and limited protocol handling for third-party apps.
- EventBridge = best for SaaS multi-consumer async decoupling.
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