HTTP 499 Client Closed Request is a non-standard status code logged by Nginx when the client closes the connection before the server finishes sending the response. This appears in Nginx access logs but is never sent to the client.
The client (browser, API client) timed out waiting for the server response and closed the connection.
The user clicked a link or closed the tab before the page finished loading.
A load balancer's health check request timed out and it closed the connection.
If clients are timing out, the server may be too slow. Check application performance and response times.
If the server legitimately needs more time, increase the client's timeout setting.
Identify and optimize the slow endpoints causing timeouts.
# Check Nginx access log for 499 responses:
# awk '$9 == 499' /var/log/nginx/access.log | awk '{print $7}' | sort | uniq -c | sort -rn | head