SQS fair queue

content/posts/sqs-simple-fair-queuing.md

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+---
+title: "SQS Simple Fair Queuing"
+date: 2023-06-16T10:23:06+07:00
+tags: ["AWS", "SQS", "Fair-queue"]
+draft: false
+---
+
+
+In a system with different user workloads, fairness is a must, unless
+you honestly want the big fish to consume all the resources and let
+the smaller ones wait in line.
+
+There are [many][0] fair-queuing algorithms out there, mostly constructed
+to solve the fairness in network schedulers. But for simple web applications,
+we only need a 2-queues system to solve the fairness problem:
+
+- One priority queue, which handles messages selectively, is rate-limited by
+a user basis
+- One regular queue, which handles all the messages sequentially
+
+Fortunately, AWS SQS comes with the dead-letter queues feature that fits
+nicely in our use case. Let's create 2 queues, one dead-letter queue as the
+regular queue, and another queue as the priority queue, with a redrive policy
+that set max receive to 1 and dead-letter queue to the regular.
+
+The fairness logic should be clear now:
+
+- The first worker pulls messages from the priority queue, and checks if
+it's rate limited. If not, go ahead and consume the message, otherwise,
+put it back. Redrive policy will ensure the message is moved to the
+dead-letter queue.
+
+- The second worker will work on the dead-letter queue, which consumes
+messages one by one.
+
+
+
+
+
+
+[0]: https://en.wikipedia.org/wiki/Fair_queuing
+[1]: https://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-dead-letter-queues.html