502 error: "Process exited unexpectedly before completing request"

Fix: configure keep-alive and idle timeout

Apply both settings on the HTTP server running inside the custom container:

1. Enable keep-alive mode on the HTTP server.

2. Disable idle timeout, or set it to more than 15 minutes. Function Compute may reuse connections after long idle periods. If the server closes the connection before Function Compute sends the next request, the connection is lost.

The exact configuration depends on the HTTP server framework. The following examples cover common frameworks.

Go (GoFrame)

s := g.Server()
// Disable idle timeout to prevent the server from closing keep-alive connections
s.SetIdleTimeout(0)
// ReadTimeout defaults to 60s; adjust if needed for long-running requests

Python (Uvicorn)

# Set --timeout-keep-alive to a value greater than 900 seconds (15 minutes)
uvicorn app:app --host 0.0.0.0 --port 9000 --timeout-keep-alive 920

Node.js (Express / HTTP)

const server = app.listen(9000, '0.0.0.0');
// Set keepAliveTimeout to a value greater than 900000 ms (15 minutes)
server.keepAliveTimeout = 920000;
server.headersTimeout = 940000;

Fix: remove exit calls and add top-level exception handling

1. Check for explicit exit calls. Search the codebase for exit operations (exit, os.Exit, sys.exit, process.exit). Remove any that run during request handling, or replace them with error responses.

2. Add top-level exception handling. Wrap the request handler in a try-catch block so that uncaught exceptions return an error response instead of crashing the process.

   Python (Flask)

   @app.errorhandler(Exception)
   def handle_exception(e):
       # Log the error and return a 500 response instead of crashing
       app.logger.error(f"Unhandled exception: {e}", exc_info=True)
       return {"error": "Internal server error"}, 500

   Node.js

   // Catch unhandled exceptions to prevent the process from exiting
   process.on('uncaughtException', (err) => {
       console.error('Uncaught exception:', err);
   });
   
   process.on('unhandledRejection', (reason) => {
       console.error('Unhandled rejection:', reason);
   });