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notificationspublish-subscribebroadcastamazon-sqs

AWS: Broadcast notifications for multiple worker processes running on multiple instances

I have multiple application instances inside of Amazon EC2, each running several worker processes. What I want is each worker process to be subscribed to some notification(e.g. configuration change). This notification should be basically broadcast message, so that once it is sent - every worker receives it.

I know SQS does not support messages broadcast. Looking through similar questions/threads I see the suggestions to use SNS instead of SQS. I'm not sure this will work for me due to the following reasons:

  • application instances are part of autoscaling group so they can be dynamically added and removed. In this case I don't see any clear way to unsubscribe every worker(I have multiple workers per instance) once instance gets terminated, which means I'll end up with the mess of dead subscribers after some time.
  • protocol to use for subscription is also not clear. HTTP endpoint looks like the only option, which means my every worker should run HTTP server on its own port. It also looks I should listen only on instance public IP, which adds one more layer of complexity and insecurity.

At the moment I have a solution based on third party - I'm using 0MQ pub/sub server. But I'm looking for some out-of-box solutions AWS provides.

Thanks, Vovan

Solution

  • The out-of-the-box AWS solution that comes to mind would be to create one SNS topic, and then for each instance, when the instance boots up, it would create its own SQS queue and subscribe the queue to the SNS topic, so that each individual queue gets a broadcast copy of each message you publish to SNS.

    You'd want unsubscribe and delete these queues on instance termination, which could be done with lifecycle hooks.

    If you didn't want to use a server to manage the processing of the lifecycle hooks (which publish the launch or termination events to SNS or SQS) you could create an AWS API Gateway endpoint to fire an AWS Lambda function, then subscribe the API Gateway endpoint to the SNS topic using https, to handle the cleanup tasks in Lambda, with no server needed.

    That's several services working together and may sound a little complicated, but would be very inexpensive and require little maintenance or attention.