This is an attempt to emulate uWSGI’s uwsgi.worker_id() that ensures that I have worker IDs from 1…--workers which is useful in logging and instrumentation where changing PIDs are annoying.

gunicorn_callbacks_for_worker_id.py

def on_starting(server):
    setattr(server, '_worker_id_set', set())


def _next_worker_id(server):
    if hasattr(server, '_worker_id_set') and isinstance(server._worker_id_set, set) and len(server._worker_id_set) > 0:
        return server._worker_id_set.pop()

    in_use = set(w._worker_id for w in tuple(server.WORKERS.values()) if hasattr(w, '_worker_id') and w.alive)
    free = set(range(1, server.num_workers + 1)) - in_use

    return free.pop()


def on_reload(server):
    setattr(server, '_worker_id_set', set(range(1, server.num_workers + 1)))


def pre_fork(server, worker):
    # Attach worker_id to worker before forking
    setattr(worker, '_worker_id', _next_worker_id(server))


def post_fork(server, worker):
    # Pass worker_id through env after forking
    os.environ[ENV_VAR_APP_WORKER_ID] = str(getattr(worker, '_worker_id', 0))