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SNS (Simple Notification Service)


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Amazon SNS is a fully managed pub/sub messaging service that enables you to decouple microservices, distributed systems, and event-driven serverless applications.

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How It Works​

  • A publisher sends a message to an SNS topic
  • The topic delivers the message to all its subscribers
  • SNS follows the publish-subscribe (pub/sub) messaging pattern
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Topic Types​

Standard Topic​

  • Default topic type
  • Nearly unlimited throughput
  • At-least-once message delivery
  • Best-effort ordering

FIFO Topic​

  • Strict message ordering (first-in-first-out)
  • Exactly-once message delivery
  • Up to 300 publishes per second (or 10 MB per second)
  • FIFO topic names must end with the .fifo suffix
  • Can only have SQS FIFO queues as subscribers
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Subscriptions​

Supported subscription protocols:

  • HTTP/HTTPS: delivers messages to a specified URL
  • Email/Email-JSON: sends messages via email
  • Amazon SQS: delivers messages to an SQS queue
  • AWS Lambda: invokes a Lambda function
  • Amazon Kinesis Data Firehose: delivers messages to a Firehose delivery stream
  • SMS: sends text messages to phone numbers
  • Platform application endpoint: delivers messages to mobile devices (push notifications)
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Message Filtering​

  • By default, a subscriber receives every message published to the topic
  • A subscription filter policy can be applied so the subscriber only receives messages that match specific attributes
  • Filter policies can be applied to message attributes or to the message body
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Fanout Pattern​

  • A common pattern where an SNS topic is combined with multiple SQS queues
  • A message published to the topic is delivered to all subscribed queues, allowing parallel asynchronous processing
  • Useful for decoupling systems that need to react to the same event independently
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Dead-Letter Queue​

  • An SQS queue that an SNS subscription can target for messages that could not be successfully delivered to subscribers
  • Useful for debugging and isolating undeliverable messages
  • Configured per subscription, not per topic
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Encryption​

  • Server-side encryption (SSE) protects the contents of messages published to a topic using AWS KMS keys
  • Messages are encrypted as soon as they are received by SNS and stored in encrypted form
  • Messages are decrypted just before delivery to subscribed endpoints
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Access Control​

  • Topic access can be controlled via:
    • IAM policies
    • SNS access control policies (resource-based policies)
  • By default, only the topic owner can publish or subscribe to a topic
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