SNS - Simple Notification Service

• Pub/Sub model
• The event produces only sends messages to one SNS topic
• Each subscriber to the topic will get all the messages be default (we can filter them, if we want)
• We can have up to 10 million subscribers per topic
• We cave up to 100K topics
• Subscribers to the topic can be:
  • SQS
  • HTTP/HTTPS
  • Lambda
  • Emails
  • SMS messages
  • Mobile Notifications
• Many different services integrate with SNS for notifications, for example:
  • CloudWatch (for alarms)
  • Auto Scaling Groups notifications
  • S3 (bucket events)
  • CloudFormation (state changes)
  • Etc…
• How to publish?
  • In order to publish we must create a topic using the SDK
  • We may create one or many subscriptions
  • We publish data to the topic
• Direct Publish (for mobile apps SDK)
  • Create a platform application
  • Create a platform endpoint
  • Publish to the platform endpoint
• Direct Publish works with Google GCM, Apple APNS, Amazon ADM

Security

• Encryption:
  • In-flight encryption using HTTPS API
  • At-rest encryption using the KMS keys
  • Client-side encryption if the client wants to perform encryption/decryption itself
• Access Controls: IAM policies to regulate access to the SNS API
• SNS Access Policies (similar to S3 bucket policies):
  • Useful for cross-account access to SNS topics
  • Useful for allowing other services (S3) to write to an SNS topic

SNS + SQS Fan Out

• Send a message to multiple SQS queues using SNS
• Push one in SNS, receive in all SQS queues which are subscribers
• Fully decouples, no data loss
• SQS allows for data persistance, delayed processing and retries of work
• Ability to add more SQS subscribers over time
• SQS queues must have an allow access policy for SNS to be able to write to the queues
• SNS cannot send messages to SQS FIFO queues (AWS limitation)!
• Use case: send S3 events to multiple queues:
  • For the same combination of even type and prefix we can only have one S3 Event rule
  • In case we want to send the same S3 event to many SQS queues, we must use SNS fan-out