Question

I’m using Google Appengine in a production environment and we are currently getting 500 errors on both our website and console. Is there anything we can do to prevent these or handle them more gracefully?

EDIT: We’re using python with Webapp

Answer 1

1. Setup error handlers: http://code.google.com/appengine/docs/python/config/appconfig.html#Custom_Error_Responses

2. When the error occurs in the app, error handlers can’t help. One solution is to wrap the application to handle uncaught exceptions:

   import logging
   
   from google.appengine.ext import webapp
   from google.appengine.ext.webapp import util
   
   def error_handler_middleware(app):
       """Wraps the application to catch uncaught exceptions."""
       def wsgi_app(environ, start_response):
           try:
               return app(environ, start_response)
           except Exception, e:
               logging.exception(e)
               # ... display a custom error message ...
               response = webapp.Response()
               response.set_status(500)
               response.out.write('Ooops! An error occurred...')
               response.wsgi_write(start_response)
               return ['']
   
       return wsgi_app
   
   app = webapp.WSGIApplication([...])
   app = error_handler_middleware(app)
   
   def main():
       util.run_wsgi_app(app)
   
   if __name__ == '__main__':
       main()
   

3. If you can, give webapp2 a try. You can set simple functions to handle app-wide exceptions.