Each page explains one concrete backend or network error, the common causes behind it, the evidence that separates lookalike failures, and the first commands worth running.
Start with the exact phrase from the log, then confirm the layer that produced it: DNS, TCP, TLS, proxy, application runtime, or host resource limit. The guides are organized to prevent a common incident mistake: changing timeout, kernel, or proxy settings before proving which component failed.
If a symptom crosses layers, use the related guide links and the topic clusters below to move from the visible error to adjacent causes.
Start with a concrete error message. Keep the query short and exact.
Use the first visible signal to choose the right guide cluster.
Start from the layer that owns the symptom, then move to adjacent causes.
Gateway errors, upstream timeouts, connection closes, and proxy routing failures.
Resets, refused connections, broken pipes, retransmissions, and packet loss.
Handshake failures, unknown authorities, verification errors, and trust-store issues.
Host-level limits, DNS failures, ports, routes, and runtime diagnostics.
A practical cannot assign requested address guide that separates wrong bind IP, missing local address, container networking, source address selection, ephemeral port exhaustion, and TIME_WAIT pressure.
Read guideA practical connect timed out guide that separates DNS, routing, firewall drops, TCP SYN loss, listener backlog pressure, load balancers, and wrong targets.
Read guideA practical DNS SERVFAIL guide that separates resolver reachability, authoritative server failure, DNSSEC validation, broken delegation, private zone issues, and transient upstream resolver errors.
Read guideA practical Nginx client intended to send too large body guide that separates upload limits, route-specific sizing, buffering, app limits, ingress limits, and unsafe global increases.
Read guideA practical Nginx host not found in upstream guide that separates startup DNS resolution, resolver directive behavior, Docker and Kubernetes DNS, variable proxy_pass, and upstream name changes.
Read guideA practical Nginx upstream sent too big header guide that separates oversized response headers, cookies, redirects, auth tokens, proxy buffers, and unsafe global buffer increases.
Read guideA practical TLS wrong version number guide that separates HTTP-to-HTTPS mismatches, TLS termination mistakes, proxy upstream schemes, STARTTLS confusion, and port mixups.
Read guideA practical SYN backlog overflow guide that separates connection bursts, listener accept pressure, SYN flood symptoms, load balancer churn, kernel counters, and unsafe backlog tuning.
Read guideA practical Linux DNS troubleshooting guide for temporary failure in name resolution, covering resolver config, systemd-resolved, search domains, containers, Kubernetes DNS, and resolver timeouts.
Read guideA practical TLS certificate expired guide that separates server certificate expiry, intermediate chain expiry, wrong SNI, stale load balancer certificates, client clock drift, and cached trust issues.
Read guideA practical CLOSE_WAIT troubleshooting guide that separates peer close behavior, application cleanup bugs, leaked response bodies, slow workers, connection pools, and file descriptor pressure.
Read guideA practical DNS server unreachable guide that separates resolver configuration, routing, firewall, UDP/TCP 53, container DNS, and upstream resolver outages.
Read guideA practical Nginx 499 guide that separates real client aborts, browser cancels, load balancer timeouts, slow upstreams, streaming responses, and proxy timeout mismatch.
Read guideA practical Nginx 504 troubleshooting guide that separates slow upstream code, dependency latency, connection problems, and unsafe timeout changes.
Read guideA practical socket hang up guide for backend clients that separates peer resets, proxy timeouts, keepalive reuse, protocol mismatch, and application aborts.
Read guideA practical certificate verify failed guide that separates hostname mismatch, expired certificates, incomplete chains, missing trust stores, containers, and runtime-specific CA behavior.
Read guideA practical TLS handshake timeout guide that separates TCP connect delay, packet loss, SNI, certificate exchange, server CPU pressure, mTLS, and proxy TLS termination issues.
Read guideA practical guide to Nginx upstream prematurely closed connection errors, focused on proving whether the app, proxy, keepalive reuse, or transport layer closed first.
Read guideA practical x509 unknown authority guide that separates incomplete server chains, missing client trust stores, internal CAs, containers, and runtime-specific TLS behavior.
Read guideA practical guide to connection reset by peer that explains TCP resets, how to prove who sent the RST, and what to check in Linux, proxies, and upstream services.
Read guideA practical guide to broken pipe errors in Linux services, focused on finding who closed first, which write path failed, and how proxies, clients, and streaming responses trigger it.
Read guideA practical curl error 28 guide that breaks timeout failures into DNS, TCP connect, TLS handshake, first byte, response body, and upstream application latency.
Read guideA practical guide to Nginx upstream timed out errors that separates connect, send, and read timeouts from slow apps, dependency latency, and overloaded upstream workers.
Read guideA practical TLS handshake failure guide that separates certificate chain problems, SNI mismatch, protocol and cipher mismatch, mTLS failures, and proxy TLS termination mistakes.
Read guideA practical guide to connection refused errors that separates missing listeners, bind address mistakes, wrong ports, container networking, and active firewall rejects.
Read guideA practical Linux file descriptor guide that separates low limits, descriptor leaks, burst traffic, socket accumulation, slow dependencies, and system-wide exhaustion.
Read guideA practical TCP retransmission guide that separates packet loss, congestion, receiver pressure, reordering, bad links, and misleading one-sided packet captures.
Read guideA practical Linux latency guide that separates RTT, TCP connect time, TLS setup, server processing, queueing, retransmissions, and slow dependencies.
Read guideA practical read timeout guide that separates established connections, first-byte delay, stalled response bodies, packet loss, proxy idle timeouts, and upstream dependency latency.
Read guideA practical guide to intermittent packet loss that explains how to prove timing, direction, path, host counters, queue drops, and application impact.
Read guideA practical i/o timeout guide for backend services that separates DNS, TCP connect, TLS, read deadlines, storage stalls, dependency latency, and overly aggressive timeout budgets.
Read guideA practical Linux bind conflict guide that separates active listeners, stale processes, restart races, TIME_WAIT confusion, SO_REUSEADDR, containers, and systemd socket activation.
Read guideA practical no route to host guide that separates missing routes, gateway failures, firewall rejects, container networks, Kubernetes policies, and unreachable subnets.
Read guideA practical Nginx 502 guide that separates down upstreams, wrong proxy targets, protocol mismatch, early closes, malformed responses, and deploy-time failures.
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