WARNING

How to Fix Nginx 499 Client Closed Request

Quick Fix Summary

TL;DR

Increase proxy_read_timeout and client_body_timeout values in your Nginx configuration.

Nginx logs a 499 status code when the client closes its connection before the server can send a full response. This is not a server error but indicates the request-response cycle was interrupted by the client.

Diagnosis & Causes

Client-side timeout or browser cancellation.

Upstream application server response is too slow.

Network instability or packet loss between client and server.

Client script or application aborting the request prematurely.

Load balancer or proxy terminating idle connections.

Recovery Steps

Step 1: Increase Nginx Timeout Directives

The most common fix is to adjust timeout values to give slow upstreams more time to respond before the client gives up.

nginx

# In your nginx.conf or site configuration (e.g., /etc/nginx/nginx.conf)
http {
    ...
    # Increase timeouts for proxy connections
    proxy_read_timeout 300s;
    proxy_connect_timeout 75s;
    proxy_send_timeout 300s;
    ...
}
# In your server or location block handling the proxy
location /your-app/ {
    proxy_pass http://upstream_backend;
    proxy_read_timeout 300s; # Override global setting if needed
    client_body_timeout 300s;
    client_header_timeout 300s;
    send_timeout 300s;
}

Step 2: Analyze Upstream Application Performance

High 499 rates often point to a slow backend. Use Nginx logs and upstream metrics to identify bottlenecks.

bash

# 1. Configure Nginx log format to include upstream response time ($upstream_response_time)
log_format main '$remote_addr - $remote_user [$time_local] "$request" '
                  '$status $body_bytes_sent "$http_referer" '
                  '"$http_user_agent" "$http_x_forwarded_for" '
                  'rt=$request_time uct="$upstream_connect_time" urt="$upstream_response_time"';
access_log /var/log/nginx/access.log main;
# 2. After reloading nginx, analyze slow requests
tail -f /var/log/nginx/access.log | grep 499
# 3. Check for patterns (specific endpoints, high $upstream_response_time)
awk '$9 == 499 {print $7, $(NF)}' /var/log/nginx/access.log | sort | uniq -c | sort -rn

Step 3: Implement Keepalive Connections to Upstream

Reusing connections to your application server reduces overhead and can improve response times, potentially preventing client timeouts.

nginx

# In your http block or upstream block
upstream backend_servers {
    server 10.0.1.10:8080;
    server 10.0.1.11:8080;
    keepalive 32; # Maintain a cache of idle keepalive connections
}
location / {
    proxy_pass http://backend_servers;
    proxy_http_version 1.1; # Required for keepalive
    proxy_set_header Connection ""; # Clear the 'Connection' header
    # Your other proxy settings...
}

Step 4: Tune OS and Nginx for High Load

Under extreme load, socket buffers can fill, causing delays. Adjust system and Nginx buffer settings.

bash

# Edit /etc/nginx/nginx.conf
events {
    worker_connections 4096;
}
http {
    # Increase buffer sizes for large headers or slow clients
    proxy_buffer_size 128k;
    proxy_buffers 4 256k;
    proxy_busy_buffers_size 256k;
    # Adjust for long-polling or streaming
    proxy_request_buffering off; # Use with caution - disables buffering of client request body
}
# Reload Nginx after changes
sudo nginx -t && \
  sudo systemctl reload nginx

Architect's Pro Tip

"A sudden spike in 499 errors is often a client-side symptom, but the root cause is usually a degraded upstream. Correlate 499 spikes with increases in `$upstream_response_time` to prove it."

Frequently Asked Questions

Is the Nginx 499 error a server-side problem?

No. The 499 status code is logged by Nginx when the client (browser, app, load balancer) closes its connection before Nginx finishes processing the request. It indicates the client gave up, often due to a slow server response.

Should I ignore 499 errors in my logs?

No. While not a server error, a high or sudden volume of 499s is a critical performance indicator. It signals that your application response time is exceeding your clients' tolerance, leading to a poor user experience and potentially lost revenue.

What's the difference between 499 and 504 Gateway Timeout?

A 499 means the *client* closed the connection. A 504 means Nginx itself timed out waiting for the *upstream server* (e.g., your app). 499s often happen just before a 504 would be logged.

Related Nginx Guides

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