Application communication

• synchronous communications

  

  ⇒ can be problematic if there are sudden spikes of traffic

• asynchronous / event based

  

  ⇒ scalable

Producing messages

• define body
• add message attributes (metadata - optional)
• delay delivery (optional)
• get back
  • message identifier
  • MD5 hash of body

Consuming messages

• poll message from SQS (maximum 10 messages at a time)
• process the message within the visibility timeout
• delete the message using message ID & receipt handle

visibility timeout

• when a consumer polls a message from a queue ⇒ the message is invisible to other consumers for a defined period ⇒ Visibility Timeout
  • 0 second - 12 hours (default 30 seconds)
  • when consumer fails to process the message, the message is still invisible until Visibility Timeout finish ⇒ be carefull to set high Visibility Timeout (eg 15 minutes)
  • if too low (30 senconds) and consumer needs time to process the message (2 minutes) ⇒ another consumer will receive and process the message more than once
• ChangeMessageVisibility API to change the visibility
• DeleteMessage API to tell SQS the message was successfully processed

Long Polling