# django.core.exceptions.DisallowedHost: Invalid HTTP_HOST header: 'x'. You may need to add 'x' to ALLOWED_HOSTS.

**Code:** `DisallowedHost` · **Category:** Python · **Seen on:** Python

The request’s Host header isn’t listed in Django’s ALLOWED_HOSTS.

## Meaning

With DEBUG=False, Django only serves hosts in ALLOWED_HOSTS. New domains, server IPs, load balancer health checks and container hostnames must be added.

## Common causes

- New domain/IP not in ALLOWED_HOSTS
- Load balancer health checks using the instance IP
- Proxy not forwarding the Host header

## Quick fix

1. Add the domain(s): ALLOWED_HOSTS = ["example.com", "www.example.com"]
2. Read from an env var per environment
3. Configure the proxy to pass Host

## Detailed fix by platform

### Python

1. `ALLOWED_HOSTS = os.environ.get("ALLOWED_HOSTS", "").split(",")`

## How to diagnose

1. **Host** — Which host is in the message?
2. **Source** — Real users or health checks?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/python/django-disallowedhost)