Error map
Rack::Timeout::RequestTimeoutException Rails: Rack::Timeout::RequestTimeoutException: Request ran for 15001ms, exceeding the 15000ms timeout (Heroku H12)
Ruby / Rails · 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)
ERROR: canceling statement due to statement timeout
A query ran longer than statement_timeout and PostgreSQL cancelled it.
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.
FATAL: terminating connection due to idle-in-transaction timeout
A session opened a transaction and sat idle longer than idle_in_transaction_session_timeout.
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`.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
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.
Docker build slow: "Sending build context to Docker daemon 2.5GB" / transferring context takes forever
docker build is uploading your whole project folder — node_modules, .git, data files — before building, because there’s no (or a…
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.
Redis: SLOWLOG GET shows KEYS * taking 1500000 microseconds — server blocked
Redis is single-threaded; one slow command delays everything else.
Redis::CannotConnectError: Error connecting to Redis on localhost:6379 (Errno::ECONNREFUSED)
Sidekiq or the Rails Redis cache/cable couldn't connect to Redis.
Rails: ActiveRecord::ConnectionNotEstablished: No connection pool for 'ActiveRecord::Base' found
ActiveRecord has no database connection configured or established for this process.
Rails: ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR: deadlock detected
Two transactions locked rows in opposite orders, so PostgreSQL aborted one.
Two steps away (36)
Cloudflare Error 524: A Timeout Occurred
Cloudflare connected to the origin, but the origin didn’t send an HTTP response within 100 seconds.
HTTP 304 Not Modified
The cached copy is still valid, so the server sends no body and the client reuses its cache.
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.
MySQL ERROR 2002 (HY000): Can't connect to local MySQL server through socket
The client couldn’t reach the MySQL server — it isn’t running, or the client is looking for the socket/port in the wrong place.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
Cloudflare Error 522: Connection Timed Out
Cloudflare’s TCP connection to your origin timed out — the origin didn’t answer at all.
AWS Lambda: Task timed out after X seconds
The function ran longer than its configured timeout (default 3 seconds) and Lambda stopped it.
MySQL ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
MySQL detected a deadlock between two transactions and rolled one back.
ERROR: could not serialize access due to concurrent update
A REPEATABLE READ/SERIALIZABLE transaction conflicted with a concurrent one and must be retried.
MySQL ERROR 1045 (28000): Access denied for user
MySQL rejected the login — wrong password, wrong user/host combination, or the user doesn’t exist.
Deadlock found when trying to get lock; try restarting transaction
Two transactions waited on each other’s locks; the database killed one so the other could continue.
Lock wait timeout exceeded; try restarting transaction (MySQL 1205)
A query waited too long for a row lock held by another transaction and gave up.
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
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.
OAuth Error: redirect_uri_mismatch
The redirect URI in your OAuth request doesn’t exactly match one registered for the client in the provider’s console.
hint: You have divergent branches and need to specify how to reconcile them.
Git 2.27+ asks you to choose merge, rebase or fast-forward-only when local and remote both have new commits.
warning: in the working copy of 'x', LF will be replaced by CRLF the next time Git touches it
Git’s line-ending conversion (core.autocrlf) will change line endings in your working copy.
no space left on device (Docker / Linux)
The disk (or inode table) is full — Docker images, build cache, logs and volumes are common culprits.
npm ERR! code ELIFECYCLE / Command failed with exit code 1
An npm script (build, start, test, postinstall) exited with an error. ELIFECYCLE is only the wrapper — the real error is printed…
gyp ERR! build error / node-gyp rebuild failed
A dependency with native C/C++ code couldn’t compile — missing build tools, Python, or an unsupported Node version.
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.
Nginx: [emerg] SSL_CTX_use_PrivateKey_file("/etc/ssl/server.key") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)
The private key does not belong to the certificate configured in the server.
Certbot: Could not automatically find a matching server block for example.com. Set the `server_name` directive to use the Nginx installer
Certbot's Nginx plugin could not find a `server` block whose `server_name` matches the domain you requested.
Laravel: Symfony\Component\ErrorHandler\Error\FatalError: Maximum execution time of 30 seconds exceeded
A web request ran longer than PHP's `max_execution_time` and was killed.
Redis: Client id=12 addr=10.0.0.5:51234 scheduled to be closed ASAP for overcoming of output buffer limits
A client (often a slow subscriber or a replica) couldn't read data fast enough, so Redis disconnected it to protect memory.
Redis: INFO memory — mem_fragmentation_ratio:2.8 (RSS much larger than used_memory)
The process uses far more RSS than the data size, due to allocator fragmentation or deleted-but-not-returned memory.
Laravel: Predis\Connection\ConnectionException: Connection refused [tcp://127.0.0.1:6379] / RedisException: Connection refused
Laravel can't connect to Redis, which it uses for cache, sessions or queues.
Redis: Error: connect ECONNREFUSED 127.0.0.1:6379 / Could not connect to Redis at 127.0.0.1:6379: Connection refused
Nothing is listening on the Redis host/port your client uses.
Redis: DENIED Redis is running in protected mode because protected mode is enabled and no password is set for the default user
Redis refuses connections from non-local clients when it has no password and is bound to all interfaces.
Rails: ActionController::InvalidAuthenticityToken (Can't verify CSRF token authenticity)
A non-GET request arrived without a valid CSRF token for the session.
Redis: Error: write EPROTO ... SSL routines:ssl3_get_record:wrong version number / Connection reset by peer (TLS vs plaintext)
The client and server disagree about TLS — plaintext client to a TLS port, or TLS client to a plaintext port.
Redis: Error: read ECONNRESET / redis.exceptions.ConnectionError: Connection reset by peer after idle time
A middlebox or Redis closed an idle connection, and the pooled client reused it.
Ruby: NameError: uninitialized constant UsersController::User (Did you mean? Users)
Ruby (or Rails autoloading) couldn't find a class or module with that name in the current scope.
Ruby: NameError: undefined local variable or method 'x' for main:Object
Ruby saw a bare identifier that is neither a local variable nor a method on the current object.
Rails: ActiveRecord::RecordNotFound: Couldn't find User with 'id'=42
`find`/`find_by!` didn't find a row, so Rails raises (and renders a 404 in production).
Map another error
Popular: 500403400ORA-009331064Critical errorFileNotFoundException assemblyTypeError