AWS SNS

Overview

• Global message delivery service

Use cases

• S3 bucket notifications (e.g. do something on object PUT)
• Mobile push notifications (e.g. breaking news, marketing, alerts)
• SMS messaging
• In front of SQS if there is another listener (e.g. logging)
• "Bus" architectures: SNS + n * SQS
  • N pub to M sub
  • 1 pub to N sub (fan-out)
  • N pub to 1 sub
• VoIP push notifications (iOS)
  • incoming call wake up the application

Model

• Publisher
• Topic 
• • may represent area of interest (e.g. critical notifications)
  • may represent individuals and subscribers with their devices
  • may map to campaign
  • max 256 characters (alphanumeric, "_", "-")
• Subscriber (endpoints)
• SMS
• Publish
• sms

Message

• Max payload = 256KB
• • possibly related to SQS max payload
• MessageId
• TopicArn
• Unsubscribe Link
• Subject (optional)
• Signature (Signature Type)

Message Attributes

• Structured metadata items, e.g.
• • timestamps
  • geospatial data
  • signatures
  • identifiers
• Sent along message body
• • Subscriber can use them to determine if he should process the rest
    • Can be filtered out even earlier - see Subscription Filter policy
  • Similar to headers in HTTP
• For SQS endpoint
• • Up to 10 name-value-type triplets
  • Type: String, Binary, Number
• For Mobile Push endpoint
• • Platform specific metadata

Subscription Attributes

• RawMessageDelivery - message received exactly as published

• • by default JSON encoding
  • Supported by: HTTP(S) and SQS
• Subscription Filter policy
  • Use message attributes to filter out unwanted messages

Topic policy

• Resource-based permissions
• Publishers
• • Owner, Other AWS Accounts, Anonymous
• Subscribers
• • Owner, Other AWS Accounts, Anonymous
  • • Conditions: delivery protocol, endpoint regex, SourceOwner (CloudTrail)
• Similiar to SQS resource policy
• Use case
• • Grant "AWS S3 Service" permissions to insert notifications about Bucket Events

HTTP Delivery Policy

• Maximum receive rate
• • number of messages sent per second
  • messages awaiting delivery are held for max 60 minutes and then dropped
  • smooths out bursts
• Level
• • Topic
  • Subscription (overrides topic unless topic prohibits override explicitely)
• Retry
• • Condition
  • • HTTP 500-599 OR < 200 OR > 599
    • Timeout (15 seconds)
    • Connection error
  • Phases (allow to shape retry behavior)
  • • Immediate retry phase (no delay phase)
    • • immediately after failed attempt
      • parameter: retries with no delay
    • Pre-Backoff Phase 
    • • before backoff function is applied
      • parameter: minimum delay retries, minimum delay (time between attempts)
    • Backoff phase
    • • control delay between retries
      • parameter: minimum delay, maximum delay,
      • parameter: retry backoff function (calculate time delay)
      • • linear, arithmetic, geometric, exponential
    • Post-backoff phase
    • • When backoff function reaches the maximum delay 
      • parameter: maximum delay

References

• https://developers.google.com/cloud-messaging/concept-options#lifetime