FM-KED-007 — 502 Bad Gateway Error (Application Unreachable)

Severity: S1 — Critical Recovery Class: B — Standard Recovery Covered by Monthly Support: Yes (known causes only) 

 

 Description 

 Nginx returns a 502 Bad Gateway error because the Django application backend becomes unreachable. 

 In the majority of observed cases, this is caused by Out Of Memory (OOM) conditions on the virtual machine hosting the application worker, leading to termination of Gunicorn or equivalent application processes. 

 

 Typical Symptoms 

 HTTP 502 responses from Nginx Application intermittently unavailable Gunicorn workers restarting or disappearing Kernel logs indicating OOM events 

 

 Primary Root Cause 

 Application requests producing excessive memory usage Large datasets loaded into memory Insufficient RAM on the worker virtual machine 

 When memory limits are exceeded, the operating system terminates the application process, leaving Nginx without a valid upstream. 

 

 Diagnostic Checklist 

 Confirm OOM Condition 

 dmesg | grep -i oom

journalctl -k | grep -i kill 

 Check Available Memory 

 free -h 

 Verify Application Server Status 

 systemctl status gunicorn 

 

 Recovery Options 

 Apply one or more of the following, depending on constraints. 

 

 Option 1: Reduce Request Scope 

 Apply stricter filters to API requests Limit requested date ranges Reduce number of portfolios, instruments, or entities per request Avoid bulk data retrieval in a single call 

 This reduces memory pressure at the application level. 

 

 Option 2: Increase RAM on Worker Virtual Machine 

 Increase memory allocation on the worker VM Restart application services after resizing Verify stability under previous load 

 This addresses the issue at the infrastructure level. 

 

 Escalation and Unknown Issues 

 If the issue persists after: 

 request scope reduction, and sufficient memory allocation 

 then the incident is classified as an unknown issue . 

 Such cases require investigation, profiling, or architectural analysis and are not covered by the standard monthly support allocation. 

 

 Preventive Notes 

 Avoid unbounded API queries Monitor memory usage trends Define safe defaults and limits at API level Prefer asynchronous processing for heavy workloads 

 

 Responsibility Boundary 

 Finmars SCSA provides best-effort diagnostics and guidance for known memory-related causes. Application design decisions and infrastructure capacity planning beyond documented scenarios require separate analysis.