Frontend cache invalidator

    Changed in version 0.7:
  • Multiple backend support added

  • Cloudflare support added

    Changed in version 1.7:
  • Amazon CloudFront support added

Many websites use a frontend cache such as Varnish, Squid, Cloudflare or CloudFront to gain extra performance. The downside of using a frontend cache though is that they don’t respond well to updating content and will often keep an old version of a page cached after it has been updated.

This document describes how to configure Wagtail to purge old versions of pages from a frontend cache whenever a page gets updated.

Setting it up

Firstly, add "wagtail.contrib.wagtailfrontendcache" to your INSTALLED_APPS:

INSTALLED_APPS = [
   ...

   "wagtail.contrib.wagtailfrontendcache"
]

Changed in version 0.8: Signal handlers are now automatically registered

The wagtailfrontendcache module provides a set of signal handlers which will automatically purge the cache whenever a page is published or deleted. These signal handlers are automatically registered when the wagtail.contrib.wagtailfrontendcache app is loaded.

Varnish/Squid

Add a new item into the WAGTAILFRONTENDCACHE setting and set the BACKEND parameter to wagtail.contrib.wagtailfrontendcache.backends.HTTPBackend. This backend requires an extra parameter LOCATION which points to where the cache is running (this must be a direct connection to the server and cannot go through another proxy).

# settings.py

WAGTAILFRONTENDCACHE = {
    'varnish': {
        'BACKEND': 'wagtail.contrib.wagtailfrontendcache.backends.HTTPBackend',
        'LOCATION': 'http://localhost:8000',
    },
}

Finally, make sure you have configured your frontend cache to accept PURGE requests:

Cloudflare

Firstly, you need to register an account with Cloudflare if you haven’t already got one. You can do this here: Cloudflare Sign up

Add an item into the WAGTAILFRONTENDCACHE and set the BACKEND parameter to wagtail.contrib.wagtailfrontendcache.backends.CloudflareBackend. This backend requires three extra parameters, EMAIL (your Cloudflare account email), TOKEN (your API token from Cloudflare), and ZONEID (for zone id for your domain, see below).

To find the ZONEID for your domain, read the Cloudflare API Documentation

# settings.py

WAGTAILFRONTENDCACHE = {
    'cloudflare': {
        'BACKEND': 'wagtail.contrib.wagtailfrontendcache.backends.CloudflareBackend',
        'EMAIL': '[email protected]',
        'TOKEN': 'your cloudflare api token',
        'ZONEID': 'your cloudflare domain zone id',
    },
}

Amazon CloudFront

Within Amazon Web Services you will need at least one CloudFront web distribution. If you don’t have one, you can get one here: CloudFront getting started

Add an item into the WAGTAILFRONTENDCACHE and set the BACKEND parameter to wagtail.contrib.wagtailfrontendcache.backends.CloudfrontBackend. This backend requires one extra parameter, DISTRIBUTION_ID (your CloudFront generated distribution id).

WAGTAILFRONTENDCACHE = {
    'cloudfront': {
        'BACKEND': 'wagtail.contrib.wagtailfrontendcache.backends.CloudfrontBackend',
        'DISTRIBUTION_ID': 'your-distribution-id',
    },
}

Configuration of credentials can done in multiple ways. You won’t need to store them in your Django settings file. You can read more about this here: Boto 3 Docs

In case you run multiple sites with Wagtail and each site has its CloudFront distribution, provide a mapping instead of a single distribution. Make sure the mapping matches with the hostnames provided in your site settings.

WAGTAILFRONTENDCACHE = {
    'cloudfront': {
        'BACKEND': 'wagtail.contrib.wagtailfrontendcache.backends.CloudfrontBackend',
        'DISTRIBUTION_ID': {
            'www.wagtail.io': 'your-distribution-id',
            'www.madewithwagtail.org': 'your-distribution-id',
        },
    },
}

Note

In most cases, absolute URLs with www prefixed domain names should be used in your mapping. Only drop the www prefix if you’re absolutely sure you’re not using it (e.g. a subdomain).

Advanced usage

Invalidating more than one URL per page

By default, Wagtail will only purge one URL per page. If your page has more than one URL to be purged, you will need to override the get_cached_paths method on your page type.

class BlogIndexPage(Page):
    def get_blog_items(self):
        # This returns a Django paginator of blog items in this section
        return Paginator(self.get_children().live().type(BlogPage), 10)

    def get_cached_paths(self):
        # Yield the main URL
        yield '/'

        # Yield one URL per page in the paginator to make sure all pages are purged
        for page_number in range(1, self.get_blog_items().num_pages + 1):
            yield '/?page=' + str(page_number)

Invalidating index pages

Another problem is pages that list other pages (such as a blog index) will not be purged when a blog entry gets added, changed or deleted. You may want to purge the blog index page so the updates are added into the listing quickly.

This can be solved by using the purge_page_from_cache utility function which can be found in the wagtail.contrib.wagtailfrontendcache.utils module.

Let’s take the the above BlogIndexPage as an example. We need to register a signal handler to run when one of the BlogPages get updated/deleted. This signal handler should call the purge_page_from_cache function on all BlogIndexPages that contain the BlogPage being updated/deleted.

# models.py
from django.dispatch import receiver
from django.db.models.signals import pre_delete

from wagtail.wagtailcore.signals import page_published
from wagtail.contrib.wagtailfrontendcache.utils import purge_page_from_cache


...


def blog_page_changed(blog_page):
    # Find all the live BlogIndexPages that contain this blog_page
    for blog_index in BlogIndexPage.objects.live():
        if blog_page in blog_index.get_blog_items().object_list:
            # Purge this blog index
            purge_page_from_cache(blog_index)


@receiver(page_published, sender=BlogPage):
def blog_published_handler(instance):
    blog_page_changed(instance)


@receiver(pre_delete, sender=BlogPage)
def blog_deleted_handler(instance):
    blog_page_changed(instance)

Invalidating individual URLs

wagtail.contrib.wagtailfrontendcache.utils provides another function called purge_url_from_cache. As the name suggests, this purges an individual URL from the cache.

For example, this could be useful for purging a single page of blogs:

from wagtail.contrib.wagtailfrontendcache.utils import purge_url_from_cache

# Purge the first page of the blog index
purge_url_from_cache(blog_index.url + '?page=1')