Error map
TimeoutException java.util.concurrent.TimeoutException
Java · layer 4, Application & API
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)
Cloudflare Error 522: Connection Timed Out
Cloudflare’s TCP connection to your origin timed out — the origin didn’t answer at all.
API Request Timed Out (ETIMEDOUT / ReadTimeout / timeout of 30000ms exceeded)
The client gave up waiting — either for the connection to open or for the response to arrive.
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
AWS Lambda: Task timed out after X seconds
The function ran longer than its configured timeout (default 3 seconds) and Lambda stopped it.
Operation cannot be fulfilled on deployments.apps "x": the object has been modified; please apply your changes to the latest version and try again
Optimistic-concurrency conflict: the object changed (new resourceVersion) between when you read it and when you tried to update i…
TaskCanceledException: The request was canceled due to the configured HttpClient.Timeout of 100 seconds elapsing
The HTTP call took longer than HttpClient.Timeout (100 s default), so .NET cancelled it.
API Gateway: {"message": "Endpoint request timed out"} (504 after 29 seconds)
The backend (usually Lambda) didn’t respond within API Gateway’s integration timeout (29 seconds by default for REST APIs).
HTTP 409 Conflict
The request conflicts with the current state of the resource — e.g. a duplicate or an edit based on an outdated version.
Cloudflare Error 524: A Timeout Occurred
Cloudflare connected to the origin, but the origin didn’t send an HTTP response within 100 seconds.
API Error: Idempotency key reused with different parameters (idempotency_key_in_use)
An Idempotency-Key header was sent again with a different request body, or while the first request with that key was still runnin…
gRPC Error: 4 DEADLINE_EXCEEDED: Deadline exceeded
The call didn’t complete before the client’s deadline — slow server, network issues, or a deadline that’s too short.
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.
Two steps away (36)
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
Cloudflare Error 520: Web Server Returned an Unknown Error
Cloudflare connected to your origin, but the origin returned an empty, unknown or invalid response.
Cloudflare Error 521: Web Server Is Down
Cloudflare couldn’t connect to your origin — the connection was refused.
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.
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.
Error: socket hang up / read ECONNRESET
The other side closed the TCP connection abruptly while your client was still using it.
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.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
fatal: unable to access 'https://github.com/…': Could not resolve host: github.com
DNS lookup for the Git host failed from this machine.
AWS: ThrottlingException / Rate exceeded
You exceeded the request rate for an AWS API; retry with exponential backoff.
MySQL ERROR 2013 (HY000): Lost connection to MySQL server during query
The connection dropped mid-query — server crash/restart, timeouts, or a proxy cutting long queries.
cURL error 28: Operation timed out after 30001 milliseconds with 0 bytes received
A PHP cURL (or Guzzle) request timed out before the remote server answered.
java.util.ConcurrentModificationException
A collection was modified while being iterated (even in a single thread).
HTTP 412 Precondition Failed
A conditional request header (If-Match, If-Unmodified-Since) didn’t match the current state of the resource.
java.lang.InterruptedException (sleep interrupted)
A blocked thread (sleep, wait, join, queue take) was interrupted by another thread.
MySQL ERROR 2006 (HY000): MySQL server has gone away
The connection to MySQL was closed — usually by a timeout or a packet larger than `max_allowed_packet`.
PHP Fatal error: Maximum execution time of 30 seconds exceeded
The script ran longer than `max_execution_time` and PHP stopped it.
ERROR: canceling statement due to statement timeout
A query ran longer than statement_timeout and PostgreSQL cancelled it.
FATAL: terminating connection due to idle-in-transaction timeout
A session opened a transaction and sat idle longer than idle_in_transaction_session_timeout.
SQL Server: Execution Timeout Expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
The command ran longer than the client’s CommandTimeout (default 30 seconds).
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,…
MySQL ERROR 1062 (23000): Duplicate entry for key
An INSERT/UPDATE would create a duplicate value in a PRIMARY or UNIQUE key.
HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
HTTP 422 Unprocessable Content
The request is well-formed, but the data fails validation (e.g. invalid email, missing required field).
ERROR: out of shared memory — HINT: You might need to increase max_locks_per_transaction.
A transaction took more locks than the lock table can hold — usually touching many tables/partitions at once.
Performance: N+1 query problem (one query per row in a loop)
Code runs one query to load a list, then one more query per item — hundreds of queries per page.
Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. All pooled connections were in use and max pool size was reached.
The application’s connection pool was exhausted — all connections busy or leaked.
HTTP 428 Precondition Required
The server requires a conditional request (If-Match / If-Unmodified-Since) to prevent lost updates, and you didn’t send one.
ERROR: could not serialize access due to concurrent update
A REPEATABLE READ/SERIALIZABLE transaction conflicted with a concurrent one and must be retried.
Optimistic lock conflict: OptimisticLockException / StaleObjectStateException / version mismatch
Someone else changed the record after you read it, so your update — based on an old version — was rejected to avoid overwriting t…
Error Domain=NSURLErrorDomain Code=-1001 "The request timed out."
The server didn’t respond within URLSession’s timeout (60 s default) — slow server, unreachable host on this network, or a stalle…
gRPC Error: 14 UNAVAILABLE: No connection established / failed to connect to all addresses
The gRPC client couldn’t reach the server — wrong address/port, TLS vs plaintext mismatch, server down, or a proxy that doesn’t s…
gRPC Error: 12 UNIMPLEMENTED: unknown service x / Method not found
The server doesn’t have the service or method the client called — proto mismatch, wrong package name, or calling the wrong server.
HTTP 502 Bad Gateway
A proxy or gateway (Nginx, load balancer, CDN) got an invalid response — or no response — from the upstream server behind it.
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…
400 Bad Request: The plain HTTP request was sent to HTTPS port (Nginx 497)
Plain http:// traffic arrived on a port Nginx expects to be TLS (443 or a custom SSL port).
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