Multiple EC2 instances connecting to single SQS

Question

We are using cloudformation template to create multiple EC2 instances. We have Auto scaling and ELB defined. Each EC2 instance runs with its own Tomcat server and a web application. We connect to SQS to pull messages and write to RDS database from this web app.

Problem statement - We do not want both EC2 instances pulling the same message from SQS and writing to RDS. Could you please direct me on how to make this process efficient?

Possible duplicate of [What is a good practice to achieve the "Exactly-once delivery" behavior with Amazon SQS?](http://stackoverflow.com/questions/13484845/what-is-a-good-practice-to-achieve-the-exactly-once-delivery-behavior-with-ama) — Mark B, Feb 01 '16 at 22:26

score 0 · Accepted Answer · edited Mar 25 '16 at 14:08

Your question is reasonable, check out an explanation below.

Immediately after the component receives the message, the message is still in the queue. In order to prevent a situation you described, Amazon SQS blocks them with a visibility timeout, which is a period of time during which Amazon SQS prevents other consuming components from receiving and processing that message. Once your instance processed a message it should invoke a command that deletes a message from the queue. If for some reason, instance didn't finish a job during visibility timeout, the message becomes available for other instances again.

You can find more information here: http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/AboutVT.html

Thank you for the explanation. This is clear to me now. – uma Feb 02 '16 at 15:37 — uma, Feb 02 '16 at 15:37

Multiple EC2 instances connecting to single SQS

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