SQS vs SNS vs EventBridge: How to Choose the Right Messaging Service

Key Takeaway

Use SQS for 1:1 message queuing (decoupling), SNS for 1:N Pub/Sub (fan-out), and EventBridge for event-based routing (rule-based filtering + SaaS integration). Combining them is common (e.g., SNS → SQS fan-out).

3 Messaging Patterns

1. Message Queue (SQS):
[Producer] → [Queue] → [Consumer]
→ 1:1, consumer pulls messages (Pull)

2. Pub/Sub (SNS):
[Publisher] → [Topic] → [Subscriber 1]
                      → [Subscriber 2]
                      → [Subscriber 3]
→ 1:N, topic pushes messages (Push)

3. Event Bus (EventBridge):
[Event Source] → [Event Bus] → Rule 1 → [Target A]
                             → Rule 2 → [Target B]
→ Rule-based routing, content filtering

Amazon SQS

Key Features

Item	Description
Pattern	Message Queue (Point-to-Point)
Delivery	Pull (consumer retrieves messages)
Message Retention	Up to 14 days (default 4 days)
Message Size	Up to 256KB
Ordering	Standard: ❌, FIFO: ✅
Deduplication	Standard: ❌, FIFO: ✅
Throughput	Standard: Unlimited, FIFO: 3,000/sec (batched)

Standard vs FIFO

Standard Queue:
[Message A, B, C] → Order NOT guaranteed ❌, At-least-once delivery
→ Unlimited throughput
→ Suitable for most use cases

FIFO Queue:
[Message A, B, C] → Order guaranteed ✅, Exactly-once delivery
→ 300/sec (3,000/sec with batching)
→ Order processing, financial transactions
→ Queue name must end with .fifo

DLQ (Dead-Letter Queue)

[SQS Main Queue]
      │
      ├── Processing Success → Message deleted
      │
      └── Processing Failure (maxReceiveCount exceeded)
              │
              ▼
         [DLQ] ← Failed messages isolated
              → Analyze/reprocess later

Visibility Timeout

Consumer A retrieves message
→ Message invisible to other consumers (default 30 seconds)
→ Complete processing + delete within 30 seconds → Success
→ Exceeds 30 seconds → Becomes visible again → Another consumer can process

Amazon SNS

Key Features

Item	Description
Pattern	Pub/Sub (Publish/Subscribe)
Delivery	Push (pushes to subscribers)
Subscriber Count	Up to 12,500,000 per topic
Message Size	Up to 256KB
Message Retention	❌ (lost on delivery failure)
Filtering	Subscription filter policies

Subscription Protocols

Protocol	Description
SQS	Deliver to SQS queue
Lambda	Invoke Lambda function
HTTP/S	POST to HTTP endpoint
Email	Send email
SMS	Send text message
Kinesis Data Firehose	Deliver to stream

SNS + SQS Fan-out Pattern

Order Completed Event:

[Order Service] → [SNS Topic: OrderComplete]
                      │
                      ├── [SQS: Payment Queue] → [Payment Service]
                      ├── [SQS: Inventory Queue] → [Inventory Service]
                      ├── [SQS: Notification Queue] → [Notification Service]
                      └── [Lambda: Analytics Recording]

→ Each service processes independently
→ One failure doesn't affect other services

Message Filtering

SNS Topic: Order Events

Subscription 1 (Payment Service):
Filter: {"order_type": ["premium"]}
→ Receives only premium orders

Subscription 2 (General Processing):
Filter: None
→ Receives all orders

Amazon EventBridge

Key Features

Item	Description
Pattern	Event Bus
Event Sources	AWS services, SaaS, custom apps
Targets	18+ AWS services
Filtering	Event patterns (content-based)
Schema	Schema registry + code generation
Archiving	✅ Event archiving and replay

Event Rules

EventBridge Rule Examples:

Rule 1: EC2 State Change
Event Pattern: {"source": ["aws.ec2"], "detail-type": ["EC2 Instance State-change"]}
Target: SNS → Admin notification

Rule 2: S3 Object Created
Event Pattern: {"source": ["aws.s3"], "detail": {"bucket": {"name": ["my-bucket"]}}}
Target: Lambda → File processing

Rule 3: Schedule
Schedule: cron(0 9 * * ? *)
Target: Lambda → Daily 9 AM report generation

EventBridge Differentiators

Features EventBridge has that SNS doesn't:

1. SaaS Integration (Zendesk, Shopify, Datadog, etc.)
2. Schema Registry (auto-discover event structure)
3. Event Archiving & Replay
4. Schedule-based triggers (cron)
5. API Destinations (external API calls)
6. Global Endpoints (cross-region)

3 Services Comparison

Item	SQS	SNS	EventBridge
Pattern	Queue (1:1)	Pub/Sub (1:N)	Event Bus
Delivery	Pull	Push	Push
Message Retention	Up to 14 days	❌	Archiving available
Filtering	❌	Subscription filters	Event patterns (powerful)
Ordering	FIFO only	FIFO topics	❌
SaaS Integration	❌	❌	✅
Scheduling	❌	❌	✅ (cron/rate)
Target Count	1	12.5M subscribers	5 targets/rule
Cost	Per request	Publish + delivery	$1/million events

Selection Guide

Messaging Service Selection:
        │
        ▼
1:1 Async Processing + Decoupling?
        │
       Yes → [SQS]
        │     ├── Need ordering? → FIFO
        │     └── No ordering needed? → Standard
        No
        │
        ▼
1:N Message Broadcast?
        │
       Yes → [SNS]
        │     └── Fan-out to multiple SQS? → SNS + SQS
        No
        │
        ▼
Event-driven Architecture / SaaS Integration / Scheduling?
        │
       Yes → [EventBridge]
        │
        No
        │
        ▼
Real-time Streaming Data?
        │
       Yes → [Kinesis]

Combination Patterns

SNS + SQS (Most Common)

[Producer] → [SNS] → [SQS 1] → [Consumer 1]
                   → [SQS 2] → [Consumer 2]
→ Fan-out + independent processing + message retention

EventBridge + SQS

[AWS Service Events] → [EventBridge] → Rule → [SQS] → [Lambda]
→ Event filtering + reliable processing

SAA-C03 Exam Focus Points

1. ✅ Decoupling: "Component separation + async = SQS"
2. ✅ Fan-out: "1:N broadcast = SNS, SNS + SQS combination"
3. ✅ FIFO: "Order guarantee + deduplication = SQS FIFO"
4. ✅ DLQ: "Isolate failed messages = Dead-Letter Queue"
5. ✅ EventBridge: "SaaS integration, scheduling, event-driven = EventBridge"

Frequently Asked Questions

Q: Should I use SQS and SNS together?

For fan-out scenarios, combine SNS + SQS. When SNS delivers messages to multiple SQS queues, each consumer processes independently, and failed messages stay in the queue for retry.

Q: Can EventBridge replace SNS?

In many cases yes, but SNS has unique features like SMS/email delivery and massive subscriber support. Use EventBridge for AWS service event-based routing, SNS for A2P notifications.

Q: Can SQS messages be delivered more than once?

Standard Queue uses at-least-once delivery, so duplicates are possible. Use FIFO Queue for exactly-once delivery, or implement idempotency in consumers.

Q: How should I set SQS visibility timeout?

Set it longer than the message processing time. If too short, messages being processed become visible to other consumers. Default is 30 seconds, maximum is 12 hours.

Q: What should I consider when integrating Lambda with SQS?

Lambda uses SQS as an event source to automatically poll messages. Configure batch size, concurrency, and error handling (DLQ settings) appropriately. FIFO queues process only one Lambda per message group ID.

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Related Posts

• S3 Event Notifications: Lambda, SQS, SNS Integration
• Lambda Function Optimization
• Auto Scaling Group Setup and Policies

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References

• Amazon SQS, SNS, or EventBridge Decision Guide
• Choosing Serverless Messaging Services
• Amazon SQS FAQ