How to resolve SuspiciousOperation: Invalid HTTP_HOST header error?

I was trying to deploy my django app on pythonanywhere.

Traceback from apache error log:

2013-07-23 09:31:35,058 :Internal Server Error: /favicon.ico
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py", line 89, in get_response
    response = middleware_method(request)
  File "/usr/local/lib/python2.7/dist-packages/django/middleware/common.py", line 55, in process_request
    host = request.get_host()
  File "/usr/local/lib/python2.7/dist-packages/django/http/__init__.py", line 179, in get_host
    "Invalid HTTP_HOST header (you may need to set ALLOWED_HOSTS): %s" % host)
SuspiciousOperation: Invalid HTTP_HOST header (you may need to set ALLOWED_HOSTS): monty_singh.pythonanywhere.com

I tried ['*'] and ['monty_singh.pythonanywhere.com'] as values for ALLOWED_HOSTS but the app is still not working. No matter what value I set for ALLOWED_HOSTS I get the same error.

Solution

When Django validates the host from the HTTP request it attempts to match it against the following regex which you can find in the source here:

host_validation_re = re.compile(r"^([a-z0-9.-]+|\[[a-f0-9]*:[a-f0-9:]+\])(:\d+)?$")

The underscore in your username is causing Django to reject the host name on the request. You can create a new PythonAnywhere account with a new username or use a different web framework.