What is Amazon SNS and what functionality does it provide?

Scalable, fully managed Pub/Sub messaging service.

Main features:

• Publishing messages: Senders (publishers) can publish messages to SNS topics.
• Subscribing to topics: Receivers (subscribers) can subscribe to topics of interest to receive published messages.
• Various delivery protocols: Supports message delivery via different protocols:
  • HTTP/HTTPS
  • Email
  • SMS
  • Amazon SQS
  • AWS Lambda
• Message filtering: Subscribers can apply filtering rules to receive only messages from the topic that match certain attributes.
• FIFO subscriptions: Guarantee strict ordering and no message duplication in topics. Used together with SQS FIFO queues.
• Access policies: Access control to SNS topics via IAM policies.
• Encryption: Encrypting messages both in transit and at rest (using KMS).

Applications:

• Decoupling applications (loose coupling).
• Notification systems.
• Distributed workflows.
• Stream data processing.

Example AWS CLI publish command:

# Publishing a simple message
aws sns publish \
  --topic-arn arn:aws:sns:us-east-1:123456789012:MyTopic \
  --message "Hello from SNS!"