Django HTTP/2 Server Push redirects

A Django middleware that adds a HTTP/2 Server Push header to plain Django redirect responses.

This approach requires Django to be proxied by a server with HTTP/2 Server Push support. E.g. nginx>=1.13.9, apache2>=2.4.26 with mod_http2 enabled or a CDN services like Cloudflare.

Installation

This package is available on PyPI and can be installed with pip:

pip install django-push-redirect

Configuration

First configure your webserver to enable HTTP/2 and enable server push.

This looks something like this for nginx:

server {
  listen 443 ssl http2;
  listen [::]:443 ssl http2;
  ...

  location @python {
    proxy_set_header X-Forwarded-Proto $scheme;
    http2_push_preload on;
    ...
  }
}

The configuration for Apache and other servers/services is left as an exercise for the reader (in other words, I don't know, please contribute if you do!).

Now make sure Django is able to detect if a request is secure by configuring the SECURE_PROXY_SSL_HEADER setting, e.g.:

SECURE_PROXY_SSL_HEADER = ('HTTP_X_FORWARDED_PROTO', 'https')

Then add 'push_redirect.middleware.Http2ServerPushRedirectMiddleware' to your project's MIDDLEWARE, make sure it's before Django's CommonMiddleware:

MIDDLEWARE = [
    ...
    'push_redirect.middleware.Http2ServerPushRedirectMiddleware',
    'django.middleware.common.CommonMiddleware',
    ...
]

This middleware adds the Link rel=preload header on redirect responses that should be preloaded.

If everything is configured correctly you should see that redirects no longer require an extra request the the webserver.

Response opt-out

It is possible for a response to explicitly opt-out from the having a preload header added. This is done by setting allow_push_redirect to False on the response object, e.g.:

def opt_out(request):
    response = HttpResponseRedirect("/")
    response.allow_push_redirect = False
    return response

Inspiration / References

• https://twitter.com/simonw/status/1047865898717966337
• https://www.ctrl.blog/entry/http2-push-redirects
• https://www.nginx.com/blog/nginx-1-13-9-http2-server-push/
• https://httpd.apache.org/docs/2.4/howto/http2.html#push
• https://www.cloudflare.com/website-optimization/http2/serverpush/
• https://code.djangoproject.com/ticket/29925