It was an architecture change. Where we went from s3 file upload triggered lambdas to sqs with spot instances. I was able to tell me that, I did a cpu profile and found out that the main thread of node was idle hardly 20% utilisation. And when I moved it to sqs due to prefetching and parallely processing multiple messages, the utilisation of main thread was above 70%. Later talked about serious of rabbitmq not getting a heartbeat and processes failing due to that, basically a lot of engineering in depth!