What is Gunicorn?

The master process is a simple loop that listens for various process signals and reacts accordingly. It manages the list of running workers by listening for signals like TTIN, TTOU, and CHLD. TTIN and TTOU tell the master to increase or decrease the number of running workers. CHLD indicates that a child process has terminated, in this case the master process automatically restarts the failed worker.

The most basic and the default worker type is a synchronous worker class that handles a single request at a time. This model is the simplest to reason about as any errors will affect at most a single request. 

sync worker does not support persistent connections - each connection is closed after response has been sent (even if you manually add Keep-Alive or Connection: keep-alive header in your application).