Proxy Monitoring

Guides

Guides overview 2 pages

HAProxy Operations Guides

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

NGINX Operations Guides

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

HAProxy Operations Guides 18 pages

Open the HAProxy Operations Guides hub

HAProxy 400 And 408 Request Errors: How To Fix

Troubleshoot HAProxy 400 Bad Request and 408 Request Timeout spikes: tune.bufsize, PROXY protocol mismatches, HTTP/2 framing, request smuggling, and Slowloris.

HAProxy 502 Bad Gateway: Causes And Fixes

Diagnose HAProxy 502 Bad Gateway errors by separating connection failures (econ) from broken responses (eresp), using stats counters, termination flags, and show errors.

HAProxy 503 Service Unavailable: no server is available to handle this request

Diagnose and fix HAProxy 503 Service Unavailable errors: all servers DOWN, queue overflow, maxconn saturation, and routing gaps, using stats and log termination codes.

HAProxy 504 Gateway Timeout: timeout server and the backend timeout cascade

Why HAProxy emits 504 Gateway Timeout when timeout server fires, how the backend timeout cascade builds, and how to diagnose it with rtime, qcur, econ, and frontend vs backend 5xx.

HAProxy 5xx delta: telling HAProxy-generated errors from backend errors

Use the delta between frontend hrsp_5xx and backend hrsp_5xx to isolate errors HAProxy generated itself (503, 504, 502) from errors your backend servers returned.

HAProxy backend losing servers: active server count and cascade risk

How to detect and respond when HAProxy backends lose servers: the act/bck signals, why BACKEND status stays UP, and how to judge cascade risk before the last server fails.

HAProxy backend queue building (qcur): requests waiting for a free server slot

What qcur means in HAProxy stats, why the backend queue grows, how to diagnose it, and how to fix saturation before it turns into 503s.

HAProxy connection errors (econ): backend connections refused, timed out, or reset

Troubleshoot rising HAProxy econ counters: how to tell refused from timed-out from reset backend connections, find the root cause, and prevent recurrence.

HAProxy ephemeral port exhaustion: TIME_WAIT and backend connection churn

Diagnose and fix HAProxy ephemeral port exhaustion: why backend connection churn fills TIME_WAIT, how to confirm it with econ spikes and ss, and how http-reuse, a wider port range, and tcp_tw_reuse fix it.

HAProxy health check L4TOUT and L4CON: server marked DOWN and unreachable

What L4TOUT and L4CON mean in HAProxy health check output, how to tell a timeout from an immediate refusal, and how to find whether the fault is the server, the network, or HAProxy itself.

HAProxy health check L7STS: server DOWN on the wrong HTTP status

What HAProxy's L7STS health check code means, why a server goes DOWN on an unexpected HTTP status, and how to tell L7STS apart from L7RSP and L7TOUT.

HAProxy health checks green but the application is broken: when UP does not mean healthy

All HAProxy servers show UP but users get 5xx. Why TCP and stub HTTP health checks lie, how to confirm it with per-server hrsp_5xx, and how to fix the check.

HAProxy Idle_pct dropping: event-loop CPU saturation and the busy-polling trap

What HAProxy Idle_pct actually measures, how to diagnose event-loop CPU saturation when it drops, and why the metric is meaningless when busy-polling is enabled.

HAProxy maxconn reached: new connections queued and rejected

Diagnose and fix HAProxy maxconn saturation: CurrConns flat at Maxconn, connections queuing in the kernel backlog, and clients timing out while CPU looks fine.

HAProxy monitoring checklist: the signals every production proxy needs

A production checklist of the HAProxy signals that matter, organized by monitoring maturity: liveness, backend health, saturation, latency, errors, TLS, and certificate expiry.

HAProxy scur approaching slim: the concurrent-session saturation signal

What the HAProxy scur/slim ratio means at the global, frontend, backend, and server levels, how to alert on it, and what to do when concurrent sessions approach the configured limit.

HAProxy SSL certificate expired: total TLS failure and how to catch it first

An expired HAProxy frontend certificate means instant, total TLS failure for every client. How to confirm it, hot-fix it without a reload, and alert on expiry 30 days before it pages you.

HAProxy Too many open files: file descriptor exhaustion and refused connections

Diagnose and fix HAProxy file descriptor exhaustion: EMFILE on accept, refused connections, ulimit vs maxconn sizing, and reload-related FD leaks.

NGINX Operations Guides 4 pages

Open the NGINX Operations Guides hub

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 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 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.

Academy

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

How To Fix 504 Gateway Timeout Errors In NGINX

A Comprehensive Guide For DevOps & SRE Professionals

APIcast Monitoring

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

Cilium Proxy Monitoring

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

Clash Monitoring

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

DNSdist Monitoring

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

Envoy Monitoring

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

HAProxy Monitoring

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

ProxySQL Monitoring

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

Squid Monitoring

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

Tengine Monitoring

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

Traefik Monitoring

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

Varnish Monitoring

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

Resources

Best Envoy Proxy Monitoring Tools (2026): 10 Ranked

We compare the 10 best Envoy proxy monitoring tools for 2026, ranked on metric depth, collection granularity, trace correlation, and pricing predictability.

Best HAProxy Monitoring Tools: 10 Ranked Picks (2026)

We ranked 10 HAProxy monitoring tools on metric depth, resolution, alerting, and cost. See which delivers real per-second load balancer visibility.

Best Traefik Monitoring Tools (10 Ranked for 2026)

We ranked the 10 best Traefik monitoring tools for 2026 on per-second metric resolution, setup effort, signal breadth, cost predictability, and alerting.