Understanding and Resolving “Worker Failed to Boot” Error in Gunicorn

What Is the “Worker Failed to Boot” Error?

The “Worker Failed to Boot” error is a common issue faced by developers using the Gunicorn web server. It typically appears in the logs when Gunicorn workers fail to start or boot properly. This can result in your web application failing to run, causing downtime and potentially affecting your users’ experience.

Traceback (most recent call last):
  File "/usr/local/bin/gunicorn", line 8, in <module>
    sys.exit(run())
  File "/usr/local/lib/python3.8/site-packages/gunicorn/app/wsgiapp.py", line 61, in run
    WSGIApplication("%(prog)s [OPTIONS] [APP_MODULE]").run()
  File "/usr/local/lib/python3.8/site-packages/gunicorn/app/base.py", line 223, in run
    super(Application, self).run()
  File "/usr/local/lib/python3.8/site-packages/gunicorn/app/base.py", line 72, in run
    Arbiter(self).run()
  File "/usr/local/lib/python3.8/site-packages/gunicorn/arbiter.py", line 232, in run
    self.halt(reason=inst.reason, exit_status=inst.exit_status)
  File "/usr/local/lib/python3.8/site-packages/gunicorn/arbiter.py", line 345, in halt
    self.stop()
  File "/usr/local/lib/python3.8/site-packages/gunicorn/arbiter.py", line 393, in stop
    time.sleep(0.1)
  File "/usr/local/lib/python3.8/site-packages/gunicorn/arbiter.py", line 245, in handle_chld
    self.reap_workers()
  File "/usr/local/lib/python3.8/site-packages/gunicorn/arbiter.py", line 525, in reap_workers
    raise HaltServer(reason, self.WORKER_BOOT_ERROR)
gunicorn.errors.HaltServer: <HaltServer 'Worker failed to boot.' 3>

Find out the cause of the error and its resolution here