AWS SNS

 AWS SNS

AWS SNS - 

• Used to broadcast messages
• Pub-sub model (publisher publishes messages to a topic, subscribers listen to the topic)
• Instant message delivery (does not queue messages)

Encryption - 

• In-flight encyption by default using HTTPS API
• At-rest encyption using KMS keys
• Client-side encryption

Access Management - 

• IAM policies to regulate access to the SNS API
• SNS Access Policies (resource based policies)
• Used for cross-account access to SNS topic
• Used for allowing other AWS services to publish to an SNS topic 

Standard Topics - 

• Highest throughput 
• At least once message delivery 
• Best effort ordering 
• Subscibers can be -
• SQS queues
• HTTP/HTTPS endpoints
• Lamda function
• Emails (using SNS)
• SMS and mobile notification
• Kinesis Data Firehouse to send the data into S3 or Redshift

Fifo Topics - 

• Guaranteed  ordering of messages in that topic 
• Publishing messages to a fifo topic reqiures - 
• Group ID - messages will be ordered and grouped for each group ID
• Message De-duplication ID - for de-deuplication of messages 
• Can only have SQS FIFO queues as subscribers
• Limited throughput (same as SQS FIFO) because only SQS FIFO queues can read from FIFO topics 
• The topic name must end with .fifo

SNS + SQS Fanout Pattern - 

• Fully decoupled, no data loss
• SQS allows for - data persistence, delayed processing and retries of work
• Make sure your SQS queues access policy allows for SNS to write

Message Filtering - 

• JSON policy used to filter messages sent to SNS topics subscriptions
• Each subscriber will have its own filter policy (if a subscriber doesn't have a filter policy, it recieves every message )
• Ex. filter messages sent to each queue by the order status 

SNS + Lamda + DLQ - 

• Lamda retries each failed message 3 times after which it is sent to the DLQ by Lamda