.. _frontend_cache_purging: Frontend cache invalidator ========================== 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.frontend_cache"`` to your INSTALLED_APPS: .. code-block:: python INSTALLED_APPS = [ ... "wagtail.contrib.frontend_cache" ] 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.frontend_cache`` app is loaded. Varnish/Squid ^^^^^^^^^^^^^ Add a new item into the ``WAGTAILFRONTENDCACHE`` setting and set the ``BACKEND`` parameter to ``wagtail.contrib.frontend_cache.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). .. code-block:: python # settings.py WAGTAILFRONTENDCACHE = { 'varnish': { 'BACKEND': 'wagtail.contrib.frontend_cache.backends.HTTPBackend', 'LOCATION': 'http://localhost:8000', }, } WAGTAILFRONTENDCACHE_LANGUAGES = [] Set ``WAGTAILFRONTENDCACHE_LANGUAGES`` to a list of languages (typically equal to ``[l[0] for l in settings.LANGUAGES]``) to also purge the urls for each language of a purging url. This setting needs ``settings.USE_I18N`` to be ``True`` to work. Its default is an empty list. Finally, make sure you have configured your frontend cache to accept PURGE requests: - `Varnish `_ - `Squid `_ .. _frontendcache_cloudflare: 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.frontend_cache.backends.CloudflareBackend``. This backend can be configured to use an account-wide API key, or an API token with restricted access. To use an account-wide API key, find the key `as described in the Cloudflare documentation `_ and specify ``EMAIL`` and ``API_KEY`` parameters. To use a limited API token, `create a token `_ configured with the 'Zone, Cache Purge' permission and specify the ``BEARER_TOKEN`` parameter. A ``ZONEID`` parameter will need to be set for either option. To find the ``ZONEID`` for your domain, read the `Cloudflare API Documentation `_ With an API key: .. code-block:: python # settings.py WAGTAILFRONTENDCACHE = { 'cloudflare': { 'BACKEND': 'wagtail.contrib.frontend_cache.backends.CloudflareBackend', 'EMAIL': 'your-cloudflare-email-address@example.com', 'API_KEY': 'your cloudflare api key', 'ZONEID': 'your cloudflare domain zone id', }, } With an API token: .. code-block:: python # settings.py WAGTAILFRONTENDCACHE = { 'cloudflare': { 'BACKEND': 'wagtail.contrib.frontend_cache.backends.CloudflareBackend', 'BEARER_TOKEN': 'your cloudflare bearer token', 'ZONEID': 'your cloudflare domain zone id', }, } .. _frontendcache_aws_cloudfront: 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.frontend_cache.backends.CloudfrontBackend``. This backend requires one extra parameter, ``DISTRIBUTION_ID`` (your CloudFront generated distribution id). .. code-block:: python WAGTAILFRONTENDCACHE = { 'cloudfront': { 'BACKEND': 'wagtail.contrib.frontend_cache.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. .. code-block:: python WAGTAILFRONTENDCACHE = { 'cloudfront': { 'BACKEND': 'wagtail.contrib.frontend_cache.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. .. code-block:: python 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 ^^^^^^^^^^^^^^^^^^^^^^^^ Pages that list other pages (such as a blog index) may need to be purged as well so any changes to a blog page are also reflected on the index (for example, a blog post was added, deleted or its title/thumbnail was changed). To purge these pages, we need to write a signal handler that listens for Wagtail's ``page_published`` and ``page_unpublished`` signals for blog pages (note, ``page_published`` is called both when a page is created and updated). This signal handler would trigger the invalidation of the index page using the ``PurgeBatch`` class which is used to construct and dispatch invalidation requests. .. code-block:: python # models.py from django.dispatch import receiver from django.db.models.signals import pre_delete from wagtail.core.signals import page_published from wagtail.contrib.frontend_cache.utils import PurgeBatch ... def blog_page_changed(blog_page): # Find all the live BlogIndexPages that contain this blog_page batch = PurgeBatch() for blog_index in BlogIndexPage.objects.live(): if blog_page in blog_index.get_blog_items().object_list: batch.add_page(blog_index) # Purge all the blog indexes we found in a single request batch.purge() @receiver(page_published, sender=BlogPage) def blog_published_handler(instance, **kwargs): blog_page_changed(instance) @receiver(pre_delete, sender=BlogPage) def blog_deleted_handler(instance, **kwargs): blog_page_changed(instance) .. _frontend_cache_invalidating_urls: Invalidating URLs ^^^^^^^^^^^^^^^^^ The ``PurgeBatch`` class provides a ``.add_url(url)`` and a ``.add_urls(urls)`` for adding individual URLs to the purge batch. For example, this could be useful for purging a single page on a blog index: .. code-block:: python from wagtail.contrib.frontend_cache.utils import PurgeBatch # Purge the first page of the blog index batch = PurgeBatch() batch.add_url(blog_index.url + '?page=1') batch.purge() The ``PurgeBatch`` class ^^^^^^^^^^^^^^^^^^^^^^^^ All of the methods available on ``PurgeBatch`` are listed below: .. automodule:: wagtail.contrib.frontend_cache.utils .. autoclass:: PurgeBatch .. automethod:: add_url .. automethod:: add_urls .. automethod:: add_page .. automethod:: add_pages .. automethod:: purge