Error map

limiting requests, excess: (503 from limit_req) Nginx: [error] limiting requests, excess: 5.370 by zone "perip", client: 203.0.113.5

Nginx / Apache · layer 3, Edge & web server

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Centre: this error. First ring: errors it is linked with (8). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.

1 · On your device 2 · Network 3 · Edge & web server 4 · Application & API 6 · Platform & cloud
limiting requests, excess: (503 from limit_req) — Nginx: [error] limiting requests, excess: 5.370 by zone "perip", client: 203.0.113.5 (Nginx / Apache)limiting re…429 — HTTP 429 Too Many Requests (HTTP)429cf-mitigated: challenge — API/app requests get 403 with cf-mitigated: challenge (Bot Fight Mode / challenge on non-browser clients) (Cloudflare)cf-mitigated: chall…499 Client Closed Request / client prematurely closed connection — Nginx: [info] client prematurely closed connection while reading response header from upstream / access log status 499 (Nginx / Apache)499 Client Closed R…too many certificates already issued — Let's Encrypt: urn:ietf:params:acme:error:rateLimited :: too many certificates (5) already issued for this exact set of identifiers in the last 168 hours (SSL / TLS)too many certificat…accept4() failed (24: Too many open files) — Nginx: [crit] accept4() failed (24: Too many open files) / open() failed (24: Too many open files) (Nginx / Apache)accept4() failed (2…ModSecurity: Access denied with code 403 — Nginx/Apache: ModSecurity: Access denied with code 403 (phase 2). Matched "Operator GE matched 5 at TX:anomaly_score" (Nginx / Apache)ModSecurity: Access…nginx: client intended to send too large body — Nginx: [error] client intended to send too large body: 5242880 bytes (413 Request Entity Too Large) (Nginx / Apache)nginx: client inten…worker_connections are not enough — Nginx: [alert] 1234#1234: *987 1024 worker_connections are not enough while connecting to upstream (Nginx / Apache)worker_connections …ImagePullBackOff — Kubernetes: ImagePullBackOff / ErrImagePull (Kubernetes)ImagePullBackOffThrottlingException — AWS: ThrottlingException / Rate exceeded (AWS)ThrottlingException403 — HTTP 403 Forbidden (HTTP)403SyntaxError: JSON — SyntaxError: Unexpected token < in JSON at position 0 (JavaScript)SyntaxError: JSON418 — HTTP 418 I'm a teapot (HTTP)418444 — Nginx 444 No Response (connection closed without response) (HTTP)444500 — HTTP 500 Internal Server Error (HTTP)500504 — HTTP 504 Gateway Timeout (HTTP)504499 — HTTP 499 Client Closed Request (Nginx) (HTTP)499Challenge failed for domain — Let’s Encrypt / Certbot: Challenge failed for domain example.com — Invalid response from http://example.com/.well-known/acme-challenge/x: 404 (SSL / TLS)Challenge failed fo…SSLCertificateFile: file does not exist — Apache: AH02240: Server should be SSL-aware but has no certificate configured / SSLCertificateFile: file '/etc/ssl/x.crt' does not exist or is empty (SSL / TLS)SSLCertificateFile:…DNS problem: NXDOMAIN looking up A — Certbot: Detail: DNS problem: NXDOMAIN looking up A for www.example.com - check that a DNS record exists for this domain (SSL / TLS)DNS problem: NXDOMA…EMFILE — Too many open files (EMFILE) (Linux)EMFILEfork: retry: Resource temporarily unavailable — fork: retry: Resource temporarily unavailable (process/thread limit) (Linux)fork: retry: Resour…1025 — Cloudflare Error 1025: Please check back later (Workers request limit) (Cloudflare)10251020 — Cloudflare Error 1020: Access Denied (Cloudflare)1020bind() failed (98: Address already in use) — nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use) (Linux)bind() failed (98: …upstream timed out — Nginx: upstream timed out (110: Connection timed out) while reading response header from upstream (Nginx / Apache)upstream timed out413 — HTTP 413 Content Too Large (Request Entity Too Large) (HTTP)413Link expired — WordPress: The link you followed has expired (WordPress)Link expired100 — HTTP 100 Continue (HTTP)100414 Request-URI Too Large / 400 Request Header Or Cookie Too Large — Nginx: 400 Bad Request — Request Header Or Cookie Too Large / client sent too long header line (Nginx / Apache)414 Request-URI Too…AH00161: server reached MaxRequestWorkers setting — Apache: [mpm_event:error] AH00484: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting (Nginx / Apache)AH00161: server rea…AH00288: scoreboard is full, not at MaxRequestWorkers — Apache: [mpm_event:error] AH00288: scoreboard is full, not at MaxRequestWorkers. Increase ServerLimit (Nginx / Apache)AH00288: scoreboard…

Directly related (8)

429HTTP

HTTP 429 Too Many Requests

You’ve hit a rate limit — too many requests in a given time window. Slow down and retry later.

cf-mitigated: challengeCloudflare

API/app requests get 403 with cf-mitigated: challenge (Bot Fight Mode / challenge on non-browser clients)

Cloudflare is answering API calls, webhooks or mobile-app requests with a challenge page (HTML 403) because bot protection treats…

499 Client Closed Request / client prematurely closed connectionNginx / Apache

Nginx: [info] client prematurely closed connection while reading response header from upstream / access log status 499

The client (browser, mobile app, load balancer) disconnected before Nginx finished the response; Nginx logs status 499.

too many certificates already issuedSSL / TLS

Let's Encrypt: urn:ietf:params:acme:error:rateLimited :: too many certificates (5) already issued for this exact set of identifiers in the last 168 hours

You hit a Let's Encrypt rate limit — too many certificates, failed validations or new orders in a period.

accept4() failed (24: Too many open files)Nginx / Apache

Nginx: [crit] accept4() failed (24: Too many open files) / open() failed (24: Too many open files)

Nginx workers hit the file-descriptor limit and can't accept or open more.

ModSecurity: Access denied with code 403Nginx / Apache

Nginx/Apache: ModSecurity: Access denied with code 403 (phase 2). Matched "Operator GE matched 5 at TX:anomaly_score"

The ModSecurity WAF (OWASP Core Rule Set) blocked the request as suspicious.

nginx: client intended to send too large bodyNginx / Apache

Nginx: [error] client intended to send too large body: 5242880 bytes (413 Request Entity Too Large)

A request body exceeded `client_max_body_size` (default 1 MB), so Nginx returned 413 before reaching your app.

worker_connections are not enoughNginx / Apache

Nginx: [alert] 1234#1234: *987 1024 worker_connections are not enough while connecting to upstream

Nginx ran out of simultaneous connection slots in a worker.

Two steps away (24)

ImagePullBackOffKubernetes

Kubernetes: ImagePullBackOff / ErrImagePull

The node can’t pull the container image — wrong name/tag, missing registry credentials, or registry unreachable.

ThrottlingExceptionAWS

AWS: ThrottlingException / Rate exceeded

You exceeded the request rate for an AWS API; retry with exponential backoff.

403HTTP

HTTP 403 Forbidden

The server understood the request but refuses to authorize it — you (or the server process) are not allowed to access this resour…

SyntaxError: JSONJavaScript

SyntaxError: Unexpected token < in JSON at position 0

`JSON.parse()` / `response.json()` received something that isn’t JSON — very often an HTML error page.

418HTTP

HTTP 418 I'm a teapot

An April Fools’ status from RFC 2324 — some sites and WAFs return it on purpose to tell bots or scrapers to go away.

444HTTP

Nginx 444 No Response (connection closed without response)

An Nginx-specific code: the server deliberately closed the connection without sending anything — a rule is dropping the request.

500HTTP

HTTP 500 Internal Server Error

The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.

504HTTP

HTTP 504 Gateway Timeout

A proxy or gateway waited too long for the upstream server to respond and gave up.

499HTTP

HTTP 499 Client Closed Request (Nginx)

Nginx-specific code logged when the client disconnected before the server finished responding.

Challenge failed for domainSSL / TLS

Let’s Encrypt / Certbot: Challenge failed for domain example.com — Invalid response from http://example.com/.well-known/acme-challenge/x: 404

Let’s Encrypt couldn’t verify you control the domain — the HTTP-01 challenge file wasn’t served, or DNS points elsewhere.

SSLCertificateFile: file does not existSSL / TLS

Apache: AH02240: Server should be SSL-aware but has no certificate configured / SSLCertificateFile: file '/etc/ssl/x.crt' does not exist or is empty

Apache cannot find the certificate or key file named in its configuration, or `SSLEngine on` is set without any certificate.

DNS problem: NXDOMAIN looking up ASSL / TLS

Certbot: Detail: DNS problem: NXDOMAIN looking up A for www.example.com - check that a DNS record exists for this domain

Let's Encrypt could not resolve the domain you asked a certificate for; no A/AAAA record exists.

EMFILELinux

Too many open files (EMFILE)

The process hit its file-descriptor limit — sockets, files and pipes all count.

fork: retry: Resource temporarily unavailableLinux

fork: retry: Resource temporarily unavailable (process/thread limit)

The user or container hit its maximum number of processes/threads (ulimit -u, pids cgroup), so new processes can’t be created.

1025Cloudflare

Cloudflare Error 1025: Please check back later (Workers request limit)

The site’s Cloudflare Workers plan exceeded its daily request limit (free plan: 100,000 requests/day).

1020Cloudflare

Cloudflare Error 1020: Access Denied

A Cloudflare firewall/WAF custom rule blocked the request — the visitor’s IP, country, user agent or request pattern matched a bl…

bind() failed (98: Address already in use)Linux

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

Nginx (or another server) can’t listen on the port because another process already holds it — often Apache, another Nginx, or a s…

upstream timed outNginx / Apache

Nginx: upstream timed out (110: Connection timed out) while reading response header from upstream

Nginx waited longer than proxy_read_timeout (60 s default) for the backend (app server, PHP-FPM) to respond, then returned 504.

413HTTP

HTTP 413 Content Too Large (Request Entity Too Large)

The request body is bigger than the server is willing to accept — usually a file upload over the configured limit.

Link expiredWordPress

WordPress: The link you followed has expired

Usually an upload (theme, plugin, media) larger than PHP’s upload/post limits — WordPress receives an empty request and shows thi…

100HTTP

HTTP 100 Continue

An interim response telling the client to go ahead and send the request body — normal when the client sent Expect: 100-continue.

414 Request-URI Too Large / 400 Request Header Or Cookie Too LargeNginx / Apache

Nginx: 400 Bad Request — Request Header Or Cookie Too Large / client sent too long header line

The request line or headers (often cookies) exceed `large_client_header_buffers`.

AH00161: server reached MaxRequestWorkers settingNginx / Apache

Apache: [mpm_event:error] AH00484: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting

Apache used all its worker slots, so new requests queue or time out.

AH00288: scoreboard is full, not at MaxRequestWorkersNginx / Apache

Apache: [mpm_event:error] AH00288: scoreboard is full, not at MaxRequestWorkers. Increase ServerLimit

The shared scoreboard (process table) has no free slot even though the request limit isn't reached.

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