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I have 20K message in SQS queue. I also have a lambda will process the SQS messages, and put data into ElasticSearch server.
I have configured SQS as the lambda's trigger, and limited the Lambda's SQS batch size to be 10. I also limited the only one instance of the lambda can be run at a giving time.
However, sometime I see over 10K in-flight messages from the AWS console. Should it be max at 10 in-flight messages?
Because of this, the lambdas will only able to process 9K of the SQS message properly.
Below is a screen capture to show that I have limited the lambda to have only 1 instance running at a giving time.
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Example Amazon SQS message event (standard queue) By default, Lambda polls up to 10 messages in your queue at once and sends that batch to your function. To avoid invoking the function with a small number of records, you can tell the event source to buffer records for up to 5 minutes by configuring a batch window.
A single Amazon SQS message queue can contain an unlimited number of messages. However, there is a quota of 120,000 for the number of inflight messages for a standard queue and 20,000 for a FIFO queue.
Creating IAM User for managing Lambda. So we need permissions for below AWS Services. But since this Lambda function will receive and consume messages from SQS, this IAM user also needs a permission to receive message from SQS, which is sqs:ReceiveMessage .
Inflight messages are the messages that have been received by a consumer, but have not been deleted or failed. In other words, they are actively being processed. For a standard SQS queue, there is a limit of 120,000 inflight messages, and and 20,000 is the limit for FIFO queues.
I've been doing some testings and contacting AWS tech support at the same time.
What I do believe at the moment is that:
Amazon Simple Queue Service supports an initial burst of 5 concurrent function invocations and increases concurrency by 60 concurrent invocations per minute. Doc
1/ The thing that does that polling, is a separate entity. It is most likely to be a lambda function that will long-poll the SQS and then, invoke our lambda functions.
2/ That polling Lambda does not take into account any of our Receiver-Lambda at all. It does not care whether the function is running at max capacity or not, or how many max concurrency is available for the Receiver-Lambda
3/ Due to that combination. The behavior is not what we expected from the Lambda-SQS integration. And worse, If you have suddenly, millions of message burst in your queue. The Receiver-Lambda concurrency can never catch up with the amount of messages that the polling Lambda is sending, result in loss of work
The test:
The result:
I will update this answer as soon as I got the confirmation from AWS support
Support answer. As of Q1 2019, TL;DR version
1/ The assumption was correct, there was a "Poller"
2/ That Poller do not take into consideration of reserved concurrency as part of its algorithm
3/ That poller have hard limit of 1000
Q2-2019 :
The above information need to be updated. Support said that the poller correctly consider reserved concurrency but it should be at least 5. The SQS-Lambda integration is still being updated and this answer will not. So please consult AWS if you get into some weird issues
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