Fix the Docker healthcheck script to supply correct Host header

Commit 8fed685f12 added a HEALTHCHECK
instruction in the Dockerfile. The healthcheck script calls http://localhost:8000/api/v3/status/, which fails if localhost is not in ALLOWED_HOSTS.

With this change, the healthcheck script is now a Django management
command. It reads Django's ALLOWED_HOSTS setting, grabs the first
element, and uses it in the "Host:" HTTP header when making a HTTP
request.

cc: #1051

CHANGELOG.md

@@ -1,6 +1,11 @@
 # Changelog
 All notable changes to this project will be documented in this file.
 
+## v3.5.2 - 2024-08-21
+
+### Bug Fixes
+- Fix the Docker healthcheck script to supply correct Host header (#1051)
+
 ## v3.5.1 - 2024-08-20
 
 ### Bug Fixes

docker/Dockerfile

@@ -33,6 +33,7 @@ RUN --mount=type=bind,target=/wheels,source=/wheels,from=builder \
     pip install --no-cache /wheels/*
 
 COPY --from=builder /opt/healthchecks/ /opt/healthchecks/
+COPY docker/fetchstatus.py /opt/healthchecks/hc/api/management/commands/
 
 RUN \
     rm -f /opt/healthchecks/hc/local_settings.py && \
@@ -44,5 +45,5 @@ RUN mkdir /data && chown hc /data
 USER hc
 
 ENV USE_GZIP_MIDDLEWARE=True
-HEALTHCHECK --interval=10s --start-period=10s --retries=1 CMD /opt/healthchecks/docker/fetchstatus.sh
+HEALTHCHECK --interval=10s --start-period=10s --retries=1 CMD ./manage.py fetchstatus
 CMD [ "uwsgi", "/opt/healthchecks/docker/uwsgi.ini"]

docker/fetchstatus.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from typing import Any
+from urllib.request import Request, urlopen
+
+from django.conf import settings
+from django.core.management.base import BaseCommand
+
+
+class Command(BaseCommand):
+    def handle(self, **options: Any) -> str:
+        host = settings.ALLOWED_HOSTS[0]
+        if host == "*":
+            host = "localhost"
+
+        req = Request("http://localhost:8000/api/v3/status/", headers={"Host": host})
+        with urlopen(req) as response:
+            assert response.status == 200
+
+        return "Status OK"

docker/fetchstatus.sh

@@ -1 +0,0 @@
-python -c "from urllib.request import urlopen; urlopen('http://localhost:8000/api/v3/status/')"