SNS

Managed pub/sub. Publishers send to a topic; SNS pushes each message to all subscribers. Decouples one event from many reactions.

flowchart LR
  P[Publisher] --> T((SNS Topic))
  T --> Q1[SQS queue]
  T --> Q2[SQS queue]
  T --> L[Lambda]
  T --> H[HTTPS endpoint]

Subscribers

• SQS, Lambda, HTTP/S, email, SMS, mobile push, and Kinesis Data Firehose.
• Push-based — no polling. SNS retries failed deliveries; pair with a DLQ per subscription.

Patterns

• Fan-out — SNS → multiple SQS queues so several services process the same event independently and durably.
• Message filtering — subscription filter policies route only matching messages (filter on attributes or message body) — subscribers get just what they care about.

Standard vs FIFO

• FIFO topics preserve ordering and dedup, but only deliver to FIFO SQS queues.
• Standard topics: higher throughput, best-effort ordering, can deliver to any subscriber type.

Notes

• Max message size 256 KB.
• Encryption in transit by default; at rest via KMS.

vs EventBridge

SNS is high-throughput, low-latency fan-out with simple filtering. EventBridge adds content-based routing, SaaS sources, schema registry, and archive/replay — at higher latency. Choose by routing complexity.