SAA

• Max retention days 14 days
• Max size 256 KB

• Cross Account Access
• S3 push notification

• MaximumReceive API
• Set threshold

• Request Queue
• Response Queues for each request (2 requests, then create 2 response queues)
• SQS Temporary Queue Client

https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-temporary-queues.html

FIFO Queue

When creating a FIFI queue, Queue name should end with `.fifo`

Has GroupID and Deduplication ID

• Need to create a Custom Metric
• Queue length: ApproximateNumberOfMessages

SAP

• SQS can be used as a write buffer for DynamoDB
  • Because SQS auto-scale
  • write an application to read from SQS then insert to DynamoDB
  • to prevent PrevisionThroughtExpection error

• SQS might be processed twice
• Need to make sure consumer is idempotency
• For example, two EC2 happens to handle the same SQS message
• Then need to insert data to DynamoDB
• this is not idempotent, because two record will be the same
• Instead, we can upsert
  into DynamoDB based on primary key
• so that, two operations are still idempotency

idempotency is a Web API design principle defined asthe ability to apply the same operation multiple times without changing the result beyond the first try.

Upsert: An operation that inserts rows into a database table if they do not already exist, or updates them if they do.

• Lambda read 10 message in batch
• Using long polling for efficiency
• DLQ should be set only on SQS side
• Invoke DLQ is async, because Lambda doesn't need response from DLQ
• Use Lambda destination
• 6x the timeout of your Lambda function