How we tamed Node.js event loop lag: a deepdive

The article discusses how the team at Trigger.dev identified and resolved performance issues in their Node.js application caused by event loop lag. Initially, crashes and high CPU usage led them to investigate errors like Prisma transaction timeouts and network traffic spikes. By analyzing AWS logs, they discovered a single IP address generating excessive traffic to a specific endpoint, causing network congestion. Further investigation revealed a nested loop issue processing logs inefficiently, leading to high CPU usage. Implementing a fix and monitoring event loop lag, they addressed various issues like limiting log sizes and optimizing payload calculations. By deploying these fixes, they observed a significant reduction in event loop lag instances. Moving forward, the team plans to optimize payload handling further to enhance application reliability. The article emphasizes the importance of distributing main-thread work efficiently in Node.js applications to prevent event loop lag and ensure smooth operation for all clients.