Azure App Service Container Fails to Start — Gunicorn/Django Timeout and Invalid Host Header Error

Hi @Damion Barrett ,

Thank you for submitting your question on Microsoft Q&A.

This looks like two separate but related issues:

1. Django is rejecting the Host header > DisallowedHost
2. App Service’s health pings can’t reach your app > “timed out waiting for HTTP pings on port 80”

Below is a concise, battle‑tested checklist to get a Django container running reliably on Azure App Service for Containers with Gunicorn, and to fix both errors.

Why the error occurs .

App Service for Containers assumes your container listens on port 80. If your app listens on another port (e.g., 8000), you must tell App Service via WEBSITES_PORT to probe that port; otherwise, health pings hit the wrong port and the site fails to start.

App Service performs warm‑up pings (default path "/robots933456.txt") until the container responds, or until the startup time limit (default ~230s) is reached. Both the warm‑up path and success status codes can be customized.

Django’s ALLOWED_HOSTS must include your app’s hostname (gracealone-api.azurewebsites.net) or a suitable pattern; otherwise, Django throws DisallowedHost

Fix -1 is allow the Azure hostname in Django

Add your Azure host to ALLOWED_HOSTS. A safe, flexible pattern is to read from an env var:

# settings.py
import os

ALLOWED_HOSTS = os.getenv(
    "ALLOWED_HOSTS",
    "gracealone-api.azurewebsites.net,.azurewebsites.net,localhost,127.0.0.1"
).split(",")

Django rejects requests whose Host header is not in ALLOWED_HOSTS. Using an env var lets you keep the same image across environments.

Fix - 2 is Make App Service probe the same port your app listens on

You’ve confirmed Gunicorn is bound to 0.0.0.0:8000. Choose one of these approaches (both work):

Option A (keep app on 8000)

• Set WEBSITES_PORT=8000 in App Service → Configuration → Application settings.
• EXPOSE 8000 in your Dockerfile.
• Keep your Gunicorn bind as 0.0.0.0:8000.

# Dockerfile
EXPOSE 8000
# (your CMD/ENTRYPOINT launching gunicorn on 0.0.0.0:8000)

App Service expects 80 unless WEBSITES_PORT is set; also ensure the Dockerfile exposes the same port.

Option B (move app to port 80)

• Change your Gunicorn bind to 0.0.0.0:80.
• EXPOSE 80 in your Dockerfile.
• You can omit WEBSITES_PORT (default is 80).

Binding to 80 matches the platform’s default probing behavior. Warm‑up pings target the configured port and path until the container is ready.

Note on PORT vs WEBSITES_PORT

• On custom containers, use WEBSITES_PORT.
• On blessed images (platform-provided stacks), PORT is used by the underlying runner. If in doubt, set both

Fix - 3: Avoid App Service startup timeouts

If your app does migrations or loads resources at startup, increase the container startup time limit:

az webapp config appsettings set \
  --resource-group gracealone-rg \
  --name gracealone-api \
  --settings WEBSITES_CONTAINER_START_TIME_LIMIT=600

WEBSITES_CONTAINER_START_TIME_LIMIT defaults to ~230s and can be increased up to 1800s.

Optionally, set a health path your app can return 200 OK quickly:

az webapp config appsettings set \
  --resource-group gracealone-rg \
  --name gracealone-api \
  --settings WEBSITE_WARMUP_PATH=/healthz WEBSITE_WARMUP_STATUSES=200

By default, any status from "/robots933456.txt" counts as ready; you can require 200/202 on a custom path for stricter checks.

Recommended startup/compose patterns

1. Let your image start itself (preferred)

Define ENTRYPOINT/CMD in your Dockerfile and do not override “Startup Command” in App Service. This avoids mismatch between portal settings and your image:

# Example ENTRYPOINT/CMD with port coming from env
ENV GUNICORN_WORKERS=3
# Bind to $PORT if present else fallback to 8000
CMD ["bash","-lc","gunicorn core.wsgi:application --workers ${GUNICORN_WORKERS} --bind 0.0.0.0:${PORT:-8000}"]

Overriding container commands is possible but easy to misconfigure; baking the start command into the image reduces surprises.

2. If you must use “Startup Command”

Make sure it matches the port strategy above and uses the correct env var:

gunicorn core.wsgi:application --workers 3 --bind 0.0.0.0:8000
# and set WEBSITES_PORT=8000

The portal override replaces your image’s entry point ensure it aligns with the exposed/bound port.

Reference :

https://v4.hkg1.meaqua.org/en-us/azure/app-service/reference-app-settings?tabs=kudu%2Cdotnet

https://stackoverflow.com/questions/40667519/why-is-django-throwing-error-disallowedhost-at

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