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NGINX

Monitor NGINX server activity and performance, including active connections, connection states, and client requests through the stub status endpoint.

Guides

Guides overview 1 page

NGINX Operations Guides

Practical guides for running, troubleshooting, and monitoring NGINX in production.

NGINX Operations Guides 32 pages

Open the NGINX Operations Guides hub

NGINX $request_time vs $upstream_response_time: isolating where latency lives

How to interpret NGINX timing variables to distinguish backend latency from client-side and disk I/O delays.

nginx 413 Request Entity Too Large: client_max_body_size explained

Understand why nginx returns 413, how client_max_body_size works across http, server, and location contexts, its interaction with proxy_request_buffering, and why your upstream application must also be configured.

nginx 499 status code: why clients close connections before the response

Diagnose nginx 499 errors where clients abandon requests before the server responds. Learn to distinguish slow upstreams from network drops and load-balancer noise.

nginx 500 Internal Server Error: how to diagnose it

Diagnose nginx 500 Internal Server Errors by distinguishing upstream application failures from nginx internal config, permission, and module errors using logs and status signals.

NGINX 502 Bad Gateway: Causes And How To Fix It

Diagnose and fix nginx 502 Bad Gateway errors by reading error logs, upstream variables, and connection state. Covers connection refusal, upstream crashes, oversized headers, and DNS resolution failures.

Nginx 503 Service Temporarily Unavailable: Causes & Fixes

Diagnose why nginx returns 503, distinguish rate-limit rejections from upstream outages, and fix the root cause without guessing.

NGINX 504 Gateway Time-Out: Causes & Fixes

Fix nginx 504 Gateway Timeout by isolating slow upstreams, tuning proxy_read_timeout, and distinguishing 504 from 502.

NGINX active connections climbing: reading, writing, waiting explained

Interpret NGINX stub_status Reading, Writing, and Waiting states to distinguish healthy keepalive reuse from slow clients, slow upstreams, and connection exhaustion.

NGINX Backend Cascade Failure: When Slow Upstreams Take Down Everything

Diagnose and fix the cascade failure where one slow upstream exhausts nginx worker connections, overloads healthy backends, and brings down your entire proxy tier.

nginx connect() failed (111: Connection refused) while connecting to upstream

Diagnose and fix nginx error 111 when connecting to upstream backends, including container networking pitfalls, IPv6 mismatches, and firewall blocks.

NGINX Connection Exhaustion: Detection, Diagnosis & Prevention

Detect, diagnose, and prevent NGINX connection exhaustion before it causes cliff-edge timeouts. Covers worker_connections limits, kernel accept queues, keepalive pileup, and upstream slowdown.

NGINX Dropped Connections: The Accepts vs Handled Gap

Diagnose NGINX connection drops by reading the stub_status accepts versus handled gap, a leading indicator of slot and file-descriptor exhaustion.

nginx limiting requests, excess -- understanding limit_req rejections

How nginx's limit_req leaky bucket rate limiting works, why rejected requests return 503 by default, and how to interpret excess rejections in error logs.

NGINX Listen Queue Overflow: Somaxconn, Backlog & Silent Connection Drops

Diagnose and fix kernel-level TCP listen queue overflows that silently drop NGINX connections before they reach worker processes.

NGINX Monitoring Checklist: The Signals Every Production Server Needs

A four-level monitoring maturity model for NGINX covering survival, operational, mature, and expert signals every production server needs.

nginx no live upstreams while connecting to upstream: what it means

Why nginx logs no live upstreams while connecting to upstream, how passive health checks mark every server unavailable, and how to recover from the 502 cascade.

NGINX proxy buffer spill to disk: proxy_buffers and temp file latency

Large upstream responses exceeding proxy_buffers spill to temporary files on disk, causing silent latency spikes with no error log entry.

NGINX proxy_cache not caching: why responses bypass the cache

Troubleshoot why NGINX proxy_cache silently skips caching and serves BYPASS or MISS for responses that should be cached.

NGINX reload not applying config: why old workers keep serving

Diagnose why NGINX configuration reloads fail silently or leave old worker processes serving traffic with stale configuration.

NGINX slow requests: from access log to root cause

Triage elevated NGINX $request_time by isolating client-side delays, upstream latency, temp-file spill, and CPU saturation using access log variables and OS signals.

NGINX SSL certificate expired: detection and emergency renewal

Detect expired or expiring SSL certificates in NGINX, diagnose deployment failures, and renew or replace them without extended downtime.

NGINX SSL/TLS handshake CPU saturation: detection and tuning

Detect when NGINX workers saturate CPU on TLS handshakes and tune session caching, protocol version, and connection reuse to recover throughput.

nginx upstream prematurely closed connection while reading response header

Fix nginx 502 errors caused by upstream closing the connection before response headers are fully read. Diagnose keepalive mismatches, backend crashes, and worker recycling.

nginx upstream sent too big header while reading response header from upstream

Fix the nginx 502 Bad Gateway error that occurs when upstream response headers exceed proxy_buffer_size, common with large cookies, JWTs, and multiple Set-Cookie headers.

nginx upstream timed out (110: Connection timed out) while connecting/reading

Diagnose and fix nginx upstream timeout errors. Learn to distinguish connect, send, and read phases, interpret retry encoding in $upstream_response_time, and tune proxy_next_upstream without causing cascades.

NGINX worker_connections & worker_processes: Sizing For Real Traffic

How to size NGINX worker_processes and worker_connections for production traffic, including the reverse-proxy multiplier, FD chain, and headroom rules.

nginx: a client request body is buffered to a temporary file — what it means

Understand why nginx buffers client request bodies to temporary files, how client_body_buffer_size controls the threshold, and when to tune or disable buffering for streaming uploads.

nginx: bind() to 0.0.0.0:80 failed (98: Address already in use)

Diagnose and fix nginx EADDRINUSE errors caused by stale masters, duplicate listen directives, port conflicts, and SO_REUSEPORT misconfigurations.

nginx: configuration file test failed - finding the syntax error

Diagnose and fix nginx configuration syntax errors when nginx -t fails, without disrupting the running server.

nginx: no resolver defined to resolve - dynamic upstream DNS

Fix the nginx 'no resolver defined to resolve' error when using variable-based proxy_pass, and understand dynamic upstream DNS resolution with the resolver directive and the resolve parameter.

Nginx: Too Many Open Files - Diagnosing File Descriptor Exhaustion

Diagnose nginx file descriptor exhaustion when accept4 fails with EMFILE, connections drop silently, and error logging stops.

Nginx: worker_connections Are Not Enough - Causes & Fixes

Diagnose and fix nginx worker_connections exhaustion, including the 2x proxy multiplier, worker_rlimit_nofile limits, and why slow backends are often the real cause.

Academy

Fix NGINX 502/504 Double-Proxy Errors With CloudFront

A systematic guide to diagnosing connection issues between the Cloudflare edge and your NGINX origin server

SSL/TLS Handshake Failures Causing NGINX 502 Errors

A deep dive into diagnosing and resolving the notorious SSL_do_handshake_failed error when proxying traffic with NGINX

Fix NGINX 503 Errors From Misconfigured limit_req

A deep dive into tuning NGINX rate limits to protect your origin without accidentally rejecting legitimate users

Tune NGINX Timeouts: Eliminate Upstream Errors

A practical guide to diagnosing and fixing NGINX 502 and 504 errors by configuring the right timeout directives for your backend services

Buffering keepalive and Hidden 500-Series Errors in NGINX

A deep dive into nginx buffering keepalive timeouts and how they can silently trigger 500 502 and 504 errors in your infrastructure

Fix NGINX 502 Bad Gateway In Kubernetes Ingress

Uncover the root causes of upstream errors in Kubernetes- from Ingress controller timeouts to misconfigured readiness probes that silently take your services offline

Blue-Green And Canary Deployments With NGINX

Stop fearing your rollouts- Learn which deployment KPIs and alerts will make your NGINX-powered progressive delivery a success

25 NGINX Directives to Audit Before Opening a Support Ticket

A practical checklist to help you find and fix common NGINX issues yourself

Fix NGINX 500 Internal Server Error: Easy Steps

Quick and Easy Fixes for the NGINX 500 Error

How To Fix 504 Gateway Timeout Errors In NGINX

A Comprehensive Guide For DevOps & SRE Professionals

NGINX Monitoring

Learn everything about monitoring & troubleshooting NGINX, what metrics are important to monitor and why, and how to monitor NGINX with Netdata.

NGINX Plus Monitoring

Learn everything about monitoring & troubleshooting NGINX Plus, what metrics are important to monitor and why, and how to monitor NGINX Plus with Netdata.

NGINX VTS Monitoring

Learn everything about monitoring & troubleshooting NGINX VTS, what metrics are important to monitor and why, and how to monitor NGINX VTS with Netdata.