Frontend cache purging¶
New in version 0.4.
Many websites use a frontend cache such as Varnish, Squid or Cloudflare 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¶
"wagtail.contrib.wagtailfrontendcache" to your INSTALLED_APPS:
INSTALLED_APPS = [ ... "wagtail.contrib.wagtailfrontendcache" ]
wagtailfrontendcache module provides a set of signal handlers which will automatically purge the cache whenever a page is published or deleted. You should register these somewhere at the top of your
# urls.py from wagtail.contrib.wagtailfrontendcache.signal_handlers import register_signal_handlers register_signal_handlers()
You then need to set the
WAGTAILFRONTENDCACHE_LOCATION setting to the URL of your Varnish/Squid cache server. This must be a direct connection to the server and cannot go through another proxy. By default, this is set to
http://127.0.0.1:8000 which is very likely incorrect.
Finally, make sure you have configured your frontend cache to accept PURGE requests:
Purging 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): yield '/?page=' + str(page_number)
Purging 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
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.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) @register(page_published, sender=BlogPage): def blog_published_handler(instance): blog_page_changed(instance) @register(pre_delete, sender=BlogPage) def blog_deleted_handler(instance): blog_page_changed(instance)
Purging individual URLs¶
wagtail.contrib.wagtailfrontendcache.utils provides another utils 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')