Django Cache Headers

Overview

Django Cache Headers allows you to set HTTP caching headers for URL patterns according to certain policies. It does not perform any caching itself - it merely sets the headers on the response which are then interpreted by eg. Varnish.

Doing a truly zero-conf Varnish turned out to be fragile, so Django Cache Headers now generates a VCL file that can be included into or adapted to your default Varnish configuration file.

Installation

1. Install or add django-cache-headers to your Python path.
2. Add cache_headers to your INSTALLED_APPS setting.
3. Add cache_headers.middleware.CacheHeadersMiddleware before SessionMiddleware and AuthenticationMiddleware and MessageMiddleware to your MIDDLEWARE_CLASSES setting.

Policies

Django Cache Headers provides four caching policies. You may define your own policies.:

1. all-users - response is marked as cached once for all users.
2. anonymous-only - response is marked as cached once only for anonymous users.
3. anonymous-and-authenticated - response is marked as cached once for anonymous users and once for authenticated users.
4. per-user - response is marked as cached once for anonymous users and for each authenticated user individually.

Settings

The timeouts key combines the policy, timeout in seconds and URL regexes in a nested dictionary:

CACHE_HEADERS = {
    "timeouts": {
        "all-users": {
            60: (
                "^/all-users/",
            )
        },
        "anonymous-only": {
            60: (
                "^/anonymous-only/",
            )
        },
        "anonymous-and-authenticated": {
            60: (
                "^/anonymous-and-authenticated/",
            )
        },
        "per-user": {
            60: (
                "^/per-user/",
            )
        },
        "custom-policy": {
            60: (
                "^/custom-policy/",
            )
        }
    }
}

Set browser-cache-seconds to specify how long the browser may cache a response before it has to revalidate with the server. It defaults to 5 seconds.:

CACHE_HEADERS = {"browser-cache-seconds": 10}

Set enable-tampering-checks to enable checks that guard against cache poising by tampering with the cookies. Keep this disabled for most unit tests. Unit test's client.login() does not trigger the normal expected login path.

CACHE_HEADERS = {"enable-tampering-checks": True}

Varnish configuration

Generate the VCL snippet:

python manage.py generate_vcl > /path/to/generated.vcl

Save the contents of sample.vcl as /etc/varnish/default.vcl. Restart Varnish for the configuration to take effect.