Why Does My Node.js Client Send Delayed FIN ACK (~500ms) to Server? Debugging & Fixes
Introduction
If you’ve ever analyzed network traffic between your Node.js client and server (using tools like Wireshark), you might have noticed an unexpected delay—around 500ms—before your client sends a FIN ACK packet to close the connection. This delay can degrade performance, especially in latency-sensitive or high-throughput applications (e.g., microservices, real-time APIs).
In this blog, we’ll demystify why Node.js clients delay FIN ACK packets, walk through step-by-step debugging, and provide actionable fixes to resolve the issue.