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Always allow the loopback in ALLOWED_HOSTS, for health checks

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/healthz is hit over 127.0.0.1 (the deploy probe) and localhost (the container's
own healthcheck) before any proxy has supplied a real Host header. With only the
public domain in ALLOWED_HOSTS, Django 400s both, the container is marked unhealthy
forever, and the deploy never goes green — which is how the first real deploy
failed.

The loopback is now appended unconditionally. It widens nothing: gunicorn binds to
the loopback only and the proxy owns the public domains, so nothing external can
present these hosts. Tested with a non-loopback ALLOWED_HOSTS.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Bernard Siebens
2026-07-15 13:15:08 +02:00
parent a1266378fc
commit 4d74f3fbde
2 changed files with 14 additions and 0 deletions
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6
rosterchief/settings.py
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@@ -30,6 +30,12 @@ SECRET_KEY = config("DJANGO_SECRET_KEY")
DEBUG = config("DJANGO_DEBUG", default=False, cast=bool)
ALLOWED_HOSTS = config("DJANGO_ALLOWED_HOSTS", cast=Csv(), default="")
# The loopback is always allowed, and it must be: the container's own healthcheck and the
# deploy probe hit /healthz over 127.0.0.1/localhost, before any proxy has supplied a real
# Host header. Without this they get a 400 and the container is marked unhealthy forever.
# It widens nothing — gunicorn binds to the loopback only; the proxy owns the public domains.
ALLOWED_HOSTS += [host for host in ("localhost", "127.0.0.1") if host not in ALLOWED_HOSTS]
INTERNAL_IPS = config("DJANGO_INTERNAL_IPS", cast=Csv(), default="127.0.0.1")
CSRF_TRUSTED_ORIGINS = config("DJANGO_CSRF_TRUSTED_ORIGINS", cast=Csv(), default="")

8
rosterchief/tests.py
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@@ -78,3 +78,11 @@ class HealthCheckTests(SimpleTestCase):
response = self.client.get(reverse("healthz"))
self.assertIn("no-cache", response["Cache-Control"])
@override_settings(ALLOWED_HOSTS=["example.com", "localhost", "127.0.0.1"])
def test_it_answers_over_the_loopback(self):
# The container healthcheck and the deploy probe hit it as 127.0.0.1/localhost, before
# a proxy supplies a real Host. If ALLOWED_HOSTS rejects those, /healthz 400s and the
# container is unhealthy forever — which is exactly how the first deploy failed.
for host in ("127.0.0.1", "localhost"):
self.assertEqual(self.client.get(reverse("healthz"), HTTP_HOST=host).status_code, 200, host)