SQS vs SNS vs EventBridge

SQS vs SNS vs EventBridge

Step 1 of 10

An order is placed. Billing and shipping both care — and the order service should not need to know either of them exists.

The Idea

SQS is a queue that consumers pull from: a received message is hidden for the visibility timeout and deleted when done. Standard queues deliver at least once, so consumers must be idempotent. SNS is pub/sub: a topic pushes a copy to every subscriber. EventBridge is an event bus whose rules match an event's content and route it to targets.

Real-World Example

An order service publishes one event to an SNS topic; billing and shipping each own an SQS queue subscribed to it. If shipping is down, its copy waits. A message that keeps failing moves to a dead-letter queue after maxReceiveCount receives.

The Tradeoff

Fan-out decouples teams but gives each queue its own copy to process and monitor. FIFO queues add ordering within a message group and exactly-once processing. EventBridge routes by content to many targets without glue code.

Hands-On

# illustrative — ARNs are placeholders; the queue's access policy must
# allow the topic to send to it
aws sns subscribe --topic-arn arn:aws:sns:us-east-1:123456789012:orders \
  --protocol sqs --notification-endpoint arn:aws:sqs:us-east-1:123456789012:billing
aws sqs set-queue-attributes \
  --queue-url https://sqs.us-east-1.amazonaws.com/123456789012/billing \
  --attributes file://redrive.json
# redrive.json: {"RedrivePolicy": "{\"deadLetterTargetArn\":
#   \"arn:aws:sqs:us-east-1:123456789012:billing-dlq\",\"maxReceiveCount\":\"5\"}"}

Your turn

Put the steps in the right order.

1. 1Shipping's copy waits in its queue while shipping is down↑↓
2. 2SNS pushes a copy into each subscribed queue↑↓
3. 3After repeated failures a bad message moves to the DLQ↑↓
4. 4The order service publishes one event to the topic↑↓

Check order

Mini quiz

1 / 3

Standard SQS queues deliver messages:

• AExactly once, in order
• BAt least once, so a message can arrive twice
• CAt most once
• DOnly to Lambda functions

Sources

• Amazon SQS visibility timeout — Amazon SQS Developer Guide
• Using dead-letter queues in Amazon SQS — Amazon SQS Developer Guide
• What is Amazon SNS? — Amazon SNS Developer Guide
• Rules in Amazon EventBridge — Amazon EventBridge User Guide