Context
AWS Simple Queue Service (SQS) provides fully managed message queuing for microservices, distributed systems, and serverless applications.
Best practices
Consume messages in a separate thread or process
Node is single threaded; it can only operate on one task at a time. Creating a separate process creates isolation, preventing API availability issues if, for example, consumers spike CPU or memory usage.
Consumers should be idempotent
Both EventBridge and SQS provide “at-least once” message delivery. That means duplicate messages WILL, at some point, happen. Consumers must handle this gracefully. A simple way to avoid duplicate writes is to use producer-provided IDs that consumers use to deduplicate messages.
Process messages quickly or set the proper configuration
From AWS’s SQS Best Practices:
Setting the visibility timeout depends on how long it takes your application to process and delete a message. For example, if your application requires 10 seconds to process a message and you set the visibility timeout to 15 minutes, you must wait for a relatively long time to attempt to process the message again if the previous processing attempt fails. Alternatively, if your application requires 10 seconds to process a message but you set the visibility timeout to only 2 seconds, a duplicate message is received by another consumer while the original consumer is still working on the message.
If using the sqs-consumer library and you know how long it takes to process a message batch, configure the visibility timeout. Otherwise, configure the heartbeat interval.
Configure a dead-letter queue (DLQ) with maximum message retention (14 days)
Details. If a consumer fails to process a message N number of times (configured via SQS’s maxReceiveCount), the message is sent to the DLQ. This prevents “poison pill” messages from continuously failing, which negatively affects consumer throughput.
Avoid automatically consuming DLQs
If you consume DLQ messages and delete them, they’re gone forever. Instead, set the maximum 14 day message retention. This provides a safe place for messages to sit while you root cause the issue causing messages to end up there. Once a fix is deployed, you can then consume DLQ messages to bring your service’s data up-to-date.
Handle partial batch responses
If your handler returns without error, sqs-consumer deletes the messages from the queue. Throwing an error, however, fails an entire batch. To delete them instead, return a list of successful messages from the handler. For Lambdas, see this.
For Lambda, set visibility timeout to 6x the function timeout and redrive policy to at least 5
To allow your function time to process each batch of records, set the source queue's visibility timeout to at least six times the timeout that you configure on your function. The extra time allows for Lambda to retry if your function is throttled while processing a previous batch.
To give messages a better chance to be processed before sending them to the dead-letter queue, set the
maxReceiveCounton the source queue's redrive policy to at least 5.
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