Error map
502 HTTP 502 Bad Gateway
HTTP · layer 2, Network
Centre: this error. First ring: errors it is linked with (12). 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.
Directly related (12)
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
FastCGI sent in stderr: "Primary script unknown"
Nginx passed a script path to PHP-FPM that PHP-FPM couldn’t find — usually a wrong SCRIPT_FILENAME or root.
HTTP 503 Service Unavailable
The server is temporarily unable to handle the request — overloaded, in maintenance, or has no healthy backends.
Cloudflare-branded 502 Bad Gateway / 504 Gateway Timeout ("cloudflare" footer)
A plain-looking 502/504 page with “cloudflare” at the bottom comes from Cloudflare’s network itself (or an origin response it cou…
API Service Unavailable
The API service is temporarily unable to process requests because the service is unavailable, overloaded, or undergoing maintenan…
Cloudflare Error 521: Web Server Is Down
Cloudflare couldn’t connect to your origin — the connection was refused.
Cloudflare Error 520: Web Server Returned an Unknown Error
Cloudflare connected to your origin, but the origin returned an empty, unknown or invalid response.
Error: socket hang up / read ECONNRESET
The other side closed the TCP connection abruptly while your client was still using it.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
API Gateway {"message": "Internal server error"} 502 — Malformed Lambda proxy response
The Lambda behind an API Gateway proxy integration returned something that isn’t the required {statusCode, headers, body} shape,…
Elastic Beanstalk: Environment health has transitioned from Ok to Severe
Most instances in the Elastic Beanstalk environment are failing health checks or returning errors.
HTTP 421 Misdirected Request
The request reached a server that isn’t configured for that host name — usually HTTP/2 connection reuse across domains sharing a…
Two steps away (33)
HTTP 404 Not Found
The server can’t find anything at the requested URL.
SyntaxError: Unexpected token < in JSON at position 0
`JSON.parse()` / `response.json()` received something that isn’t JSON — very often an HTML error page.
PHP Fatal error: Allowed memory size of X bytes exhausted
The script tried to use more memory than PHP’s `memory_limit` allows.
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…
Fatal error: Uncaught ArgumentCountError: Too few arguments to function foo(), 1 passed and exactly 2 expected
A function was called with fewer arguments than it requires.
Warning: Array to string conversion
An array was used where a string is expected — echoing it, concatenating it, or passing it to a string function.
Kubernetes: CrashLoopBackOff
The container starts, crashes (or exits), and Kubernetes keeps restarting it with increasing back-off delays.
HTTP 429 Too Many Requests
You’ve hit a rate limit — too many requests in a given time window. Slow down and retry later.
WordPress: Briefly unavailable for scheduled maintenance. Check back in a minute.
An update was interrupted and WordPress left its `.maintenance` file behind, so the site stays in maintenance mode.
Cloudflare Error 1016: Origin DNS error
Cloudflare can’t resolve the origin hostname your DNS record points to (usually a CNAME target).
Cloudflare Error 1033: Argo Tunnel error (Cloudflare Tunnel not connected)
The hostname routes to a Cloudflare Tunnel, but no healthy cloudflared connector is running for it.
cloudflared: Unable to reach the origin service. The service may be down or it may not be responding to traffic from cloudflared (502)
The tunnel is connected, but cloudflared can’t reach your local service at the address in the ingress rule.
Cloudflare Error 522: Connection Timed Out
Cloudflare’s TCP connection to your origin timed out — the origin didn’t answer at all.
Cloudflare Error 525: SSL Handshake Failed
Cloudflare couldn’t complete a TLS handshake with your origin (SSL mode Full / Full strict).
java.net.ConnectException: Connection refused
Nothing is listening at the host:port the Java client connected to.
HTTP 301 Moved Permanently
The resource has a new permanent URL; clients and search engines should use the address in the Location header from now on.
SSL: CERTIFICATE_VERIFY_FAILED / unable to get local issuer certificate
The client couldn’t verify the server’s TLS certificate chain, so it refused the HTTPS connection.
Cloudflare Error 526: Invalid SSL Certificate
With SSL mode Full (strict), the origin’s certificate is expired, self-signed, or doesn’t match the hostname.
Error: connect ECONNREFUSED 127.0.0.1:5432
Nothing is listening at that host:port — the target service is down or you’re connecting to the wrong address.
Too many open files (EMFILE)
The process hit its file-descriptor limit — sockets, files and pipes all count.
fatal: unable to access 'https://github.com/…': Could not resolve host: github.com
DNS lookup for the Git host failed from this machine.
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
PHP Fatal error: Maximum execution time of 30 seconds exceeded
The script ran longer than `max_execution_time` and PHP stopped it.
AWS Lambda: Task timed out after X seconds
The function ran longer than its configured timeout (default 3 seconds) and Lambda stopped it.
Runtime.ImportModuleError: Unable to import module 'lambda_function': No module named 'x'
Lambda couldn’t load your handler file or one of its dependencies — the package is missing from the deployment zip/layer or the h…
Runtime.HandlerNotFound: index.handler is undefined or not exported
Lambda loaded the file but couldn’t find the function named in the handler setting.
Stack is in ROLLBACK_COMPLETE state and can not be updated
The stack’s first creation failed and rolled back; a stack in ROLLBACK_COMPLETE can only be deleted, not updated.
CloudFormation stack in UPDATE_ROLLBACK_FAILED
An update failed, and then the rollback also failed, leaving the stack stuck until you continue the rollback.
SES MessageRejected: Email address is not verified. The following identities failed the check in region
SES refused to send because the From address/domain isn’t verified — or the account is still in the SES sandbox, where recipients…
HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
Mixed Content: The page was loaded over HTTPS, but requested an insecure resource
An HTTPS page tried to load a script, API or image over plain HTTP, and the browser blocked (or warned about) it.
CLEARTEXT communication to host not permitted by network security policy
Android 9+ blocks plain `http://` requests by default; the app tried to call a non-HTTPS URL.
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