Debugging Scenarios

Intermediate 502 Bad Gateway in Nginx Reverse Proxy 15 min

Intermediate 502 Bad Gateway Behind Cloudflare 20 min

Intermediate 503 Service Unavailable During Traffic Spikes 15 min

Beginner 500 Internal Server Error in Django 10 min

Beginner 500 Internal Server Error in PHP/Apache 10 min

Beginner 404 Not Found in Single Page Applications 10 min

Beginner Getting 401 Instead of 403 (or Vice Versa) 5 min

Intermediate 403 Forbidden Due to CORS Misconfiguration 15 min

Beginner 429 Too Many Requests — Rate Limiting Hits 10 min

Intermediate 408 Request Timeout on Slow API Calls 15 min

Intermediate 301 Redirect Loop (ERR_TOO_MANY_REDIRECTS) 10 min

Beginner 413 Content Too Large — File Upload Rejected 5 min

Intermediate 504 Gateway Timeout — Upstream Not Responding 15 min

Beginner Mixed Content Errors After HTTPS Migration 10 min

Beginner 422 Unprocessable Content — API Validation Failures 5 min

Beginner 403 Forbidden Due to CSRF Token Mismatch 5 min

Beginner 400 Bad Request — Malformed JSON Body 5 min

Beginner 405 Method Not Allowed — Wrong HTTP Verb 5 min

Advanced 409 Conflict — Optimistic Locking Failure 15 min

Intermediate 511 Network Authentication Required — Captive Portal 10 min

Intermediate 304 Not Modified — Cache Serving Stale Content 10 min

Intermediate 431 Request Header Fields Too Large — Cookie Overflow 10 min

Advanced 502 Bad Gateway — WebSocket Upgrade Failure Through Proxy 15 min

Advanced 206 Partial Content — Video Streaming Buffering Issues 15 min

Advanced 426 Upgrade Required — HTTP/1.1 to HTTP/2 Migration 15 min

Beginner 550 Mailbox Not Found — Email Bouncing 10 min

Intermediate 421 Service Unavailable — SMTP Connection Refused 15 min

Advanced Email Rejected Due to SPF/DKIM/DMARC Failures 30 min

Intermediate 550 Relay Access Denied — Cannot Send Through SMTP Server 15 min

Advanced 554 Transaction Failed — Blacklisted IP 15 min

Beginner 535 Authentication Failed — App Password Required 5 min

Beginner 452 Insufficient Storage — Mailbox Full 5 min

Intermediate 503 Bad Sequence of Commands — AUTH Before STARTTLS 10 min

Beginner 421 Service Unavailable — STARTTLS Required 5 min

Intermediate 550 Domain Has No Mail — MX Record Missing 10 min

Intermediate gRPC UNAVAILABLE — Connection Failures 15 min

Intermediate gRPC DEADLINE_EXCEEDED — Timeout Issues 15 min

Beginner gRPC PERMISSION_DENIED — Auth and Authorization Issues 10 min

Intermediate RESOURCE_EXHAUSTED — gRPC Message Size Limit Exceeded 10 min

Beginner UNAUTHENTICATED — Missing or Invalid gRPC Metadata 5 min

Advanced INTERNAL — Protobuf Serialization Mismatch 15 min

Advanced FAILED_PRECONDITION — Stale State in Distributed System 15 min

Intermediate CANCELLED — Client Abandoning Slow gRPC Requests 10 min

Beginner NXDOMAIN — Domain Does Not Exist 10 min

Intermediate SERVFAIL — DNS Server Failure 15 min

Intermediate REFUSED — Recursive Query to Authoritative-Only Server 10 min

Beginner NXDOMAIN — Subdomain Typo or Missing DNS Record 5 min

Advanced SERVFAIL — Lame Delegation 15 min

Intermediate FORMERR — Malformed DNS Query 10 min

Intermediate High TTL Causing Delayed DNS Failover 10 min

Advanced NOTAUTH — Unauthorized DNS Dynamic Update 15 min

Intermediate WebSocket 1006 Abnormal Closure 15 min

Intermediate 1008 Policy Violation — Authentication Timeout 10 min

Intermediate 1009 Message Too Big — Payload Size Limit 10 min

Advanced 1015 TLS Handshake Failure — Certificate Mismatch 15 min

Intermediate 1011 Internal Error — Server Crash During Stream 10 min

Advanced 1002 Protocol Error — Invalid Frame from Proxy 15 min

Intermediate 1013 Try Again Later — Server Overloaded 10 min

Beginner 530 Login Authentication Failed 5 min

Intermediate 425 Can't Open Data Connection — Passive Mode Firewall 10 min

Beginner 550 File Unavailable — Permission Denied 5 min

Intermediate 421 Service Unavailable — Connection Limit Reached 10 min

Intermediate 426 Connection Closed — Transfer Aborted Mid-File 10 min

Beginner 227 Entering Passive Mode — Wrong IP Behind NAT 5 min

Beginner 553 File Name Not Allowed — Invalid Characters or Path 5 min

Advanced 408 Request Timeout in NAT Traversal 15 min

Intermediate 503 Service Unavailable — SIP Trunk Overloaded 10 min

Beginner 401 Unauthorized — SIP Registration Failure 5 min

Intermediate 486 Busy Here — Call Routing Loop Misdiagnosis 10 min

Advanced 488 Not Acceptable Here — Codec Mismatch 15 min