The service was failing with:
gunicorn[2192104]: [2020-12-31 13:35:28 +0000] [2192104] [ERROR] Exception in worker process
gunicorn[2192104]: Traceback (most recent call last):
gunicorn[2192104]: File "/nix/store/jmc14qf1sfnlhw27xyyj862ghkmdkj5a-python2.7-gunicorn-19.10.0/lib/python2.7/site-packages/gunicorn/arbiter.py", line 586, in spawn_worker
gunicorn[2192104]: worker.init_process()
gunicorn[2192104]: File "/nix/store/jmc14qf1sfnlhw27xyyj862ghkmdkj5a-python2.7-gunicorn-19.10.0/lib/python2.7/site-packages/gunicorn/workers/ggevent.py", line 196, in init_process
gunicorn[2192104]: self.patch()
gunicorn[2192104]: File "/nix/store/jmc14qf1sfnlhw27xyyj862ghkmdkj5a-python2.7-gunicorn-19.10.0/lib/python2.7/site-packages/gunicorn/workers/ggevent.py", line 65, in patch
gunicorn[2192104]: monkey.patch_all(subprocess=True)
gunicorn[2192104]: File "/nix/store/fysf67w3i8iv1hfvp536nl8jbzqyk1s7-python-2.7.18-env/lib/python2.7/site-packages/gevent/monkey.py", line 1160, in patch_all
gunicorn[2192104]: from gevent import events
gunicorn[2192104]: File "/nix/store/fysf67w3i8iv1hfvp536nl8jbzqyk1s7-python-2.7.18-env/lib/python2.7/site-packages/gevent/events.py", line 67, in <module>
gunicorn[2192104]: from zope.interface import Interface
gunicorn[2192104]: ImportError: No module named zope.interface
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