500 error when visiting URL - Post process forwarder container keeps restarting

On-Premise
1

The logs of the docker container is:

/usr/local/lib/python2.7/site-packages/sentry/utils/services.py:94: UnsupportedBackend: The 'sentry.digests.backends.dummy.DummyBackend' backend for <class 'sentry.digests.backends.base.Backend'> is not recommended for production use.
  "for production use.".format(self._backend, self._base)
/usr/local/lib/python2.7/site-packages/sentry/utils/services.py:94: UnsupportedBackend: The 'sentry.tsdb.dummy.DummyTSDB' backend for <class 'sentry.tsdb.base.BaseTSDB'> is not recommended for production use.
  "for production use.".format(self._backend, self._base)
The configured event stream backend does not need a forwarder process to enqueue post-process tasks. Exiting...

The container is this:
4ab917318b20 sentry-onpremise-local "/bin/sh -c 'exec /d…" About a minute ago Restarting (0) 2 seconds ago sentry_onpremise_post-process-forwarder_1

These are the messages on /var/log/messages

Apr 25 13:02:11 sentry containerd: time="2020-04-25T13:02:11.790391846+02:00" level=info msg="shim reaped" id=4ab917318b20d2249443f8260910b42d49440703a4eb5ce19ad2403e96fe32f4

Apr 25 13:02:11 sentry dockerd: time="2020-04-25T13:02:11.800527952+02:00" level=info msg="ignoring event" module=libcontainerd namespace=moby topic=/tasks/delete type="*events.TaskDelete"

Apr 25 13:02:11 sentry kernel: br-67f02b76bd07: port 16(veth141e865) entered disabled state

Apr 25 13:02:11 sentry kernel: br-67f02b76bd07: port 16(veth141e865) entered disabled state

Apr 25 13:02:11 sentry kernel: device veth141e865 left promiscuous mode

Apr 25 13:02:11 sentry kernel: br-67f02b76bd07: port 16(veth141e865) entered disabled state

Apr 25 13:02:12 sentry kernel: br-67f02b76bd07: port 16(vethcb4a31c) entered blocking state

Apr 25 13:02:12 sentry kernel: br-67f02b76bd07: port 16(vethcb4a31c) entered disabled state

Apr 25 13:02:12 sentry kernel: device vethcb4a31c entered promiscuous mode

Apr 25 13:02:12 sentry kernel: IPv6: ADDRCONF(NETDEV_UP): vethcb4a31c: link is not ready

Apr 25 13:02:12 sentry kernel: br-67f02b76bd07: port 16(vethcb4a31c) entered blocking state

Apr 25 13:02:12 sentry kernel: br-67f02b76bd07: port 16(vethcb4a31c) entered forwarding state

Apr 25 13:02:12 sentry containerd: time="2020-04-25T13:02:12.666284907+02:00" level=info msg="shim containerd-shim started" address="/containerd-shim/moby/4ab917318b20d2249443f8260910b42d49440703a4eb5ce19ad2403e96fe32f4/shim.sock" debug=false pid=15243

Apr 25 13:02:12 sentry kernel: br-67f02b76bd07: port 16(vethcb4a31c) entered disabled state

Apr 25 13:02:13 sentry kernel: IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready

Apr 25 13:02:13 sentry kernel: IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready

Apr 25 13:02:13 sentry kernel: IPv6: ADDRCONF(NETDEV_CHANGE): vethcb4a31c: link becomes ready

Apr 25 13:02:13 sentry kernel: br-67f02b76bd07: port 16(vethcb4a31c) entered blocking state

Apr 25 13:02:13 sentry kernel: br-67f02b76bd07: port 16(vethcb4a31c) entered forwarding state
2

So I think these 2 are related:

Apr 25 13:13:37 sentry containerd: time="2020-04-25T13:13:37.414789404+02:00" level=info msg="shim containerd-shim started" address="/containerd-shim/moby/682dbf22e4a7e3b39258042b8531305dbfe6dfd483ce6283e43ac2f6955d14d6/shim.sock" debug=false pid=348

Apr 25 13:13:37 sentry kernel: br-824e129e883f: port 16(vethb39763d) entered disabled state

Apr 25 13:13:37 sentry kernel: IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready

As the short ID for the process forwarder container is: 682dbf22e4a7

3

I had to copy sentry.conf.example.py to sentry.conf.py
That solved it.