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Introducing Cache Rules: precision caching at your fingertips


6 min read
Introducing Cache Rules: precision caching at your fingertips

Ten years ago, in 2012, we released a product that put “a powerful new set of tools” in the hands of Cloudflare customers, allowing website owners to control how Cloudflare would cache, apply security controls, manipulate headers, implement redirects, and more on any page of their website. This product is called Page Rules and since its introduction, it has grown substantially in terms of popularity and functionality.

Page Rules are a common choice for customers that want to have fine-grained control over how Cloudflare should cache their content. There are more than 3.5 million caching Page Rules currently deployed that help websites customize their content. We have spent the last ten years learning how customers use those rules to cache content, and it’s clear the time is ripe for evolving rules-based caching on Cloudflare. This evolution will allow for greater flexibility in caching different types of content through additional rule configurability, while providing more visibility into when and how different rules interact across Cloudflare’s ecosystem.

Today, we’ve announced that Page Rules will be re-imagined into four product-specific rule sets: Origin Rules, Cache Rules, Configuration Rules, and Redirect Rules.

In this blog we’re going to discuss Cache Rules, and how we’re applying ten years of product iteration and learning from Page Rules to give you the tools and options to best optimize your cache.

Activating Page Rules, then and now

Adding a Page Rule is very simple: users either make an API call or navigate to the dashboard, enter a full or wildcard URL pattern (e.g. or*), and tell us which actions to perform when we see that pattern. For example a Page Rule could tell browsers– keep a copy of the response longer via “Browser Cache TTL”, or tell our cache that via “Edge Cache TTL”. Low effort, high impact. All this is accomplished without fighting origin configuration or writing a single line of code.

Under the hood, a lot is happening to make that rule scale: we turn every rule condition into regexes, matching them against the tens of millions of requests per second across 275+ data centers globally. The compute necessary to process and apply new values on the fly across the globe is immense and corresponds directly to the number of rules we are able to offer to users. By moving cache actions from Page Rules to Cache Rules we can allow for users to not only set more rules, but also to trigger these rules more precisely.

More than a URL

Users of Page Rules are limited to specific URLs or URL patterns to define how browsers or Cloudflare cache their websites files. Cache Rules allows users to set caching behavior on additional criteria, such as the HTTP request headers or the requested file type. Users can continue to match on the requested URL also, as used in our Page Rules example earlier. With Cache Rules, users can now define this behavior on one or more fields available.

For example, if a user wanted to specify cache behavior for all image/png content-types, it’s now as simple as pushing a few buttons in the UI or writing a small expression in the API. Cache Rules give users precise control over when and how Cloudflare and browsers cache their content. Cache Rules allow for rules to be triggered on request header values that can be simply defined like

any(http.request.headers["content-type"][*] == "image/png")

Which triggers the Cache Rule to be applied to all image/png media types. Additionally, users may also leverage other request headers like cookie values, user-agents, or hostnames.

As a plus, these matching criteria can be stacked and configured with operators like AND and OR, providing additional simplicity in building complex rules from many discrete blocks, e.g. if you would like to target both image/png AND image/jpeg.

For the full list of fields available conditionals you can apply Cache Rules to, please refer to the Cache Rules documentation.

Visibility into how and when Rules are applied

Our current offerings of Page Rules, Workers, and Transform Rules can all manipulate caching functionality for our users’ content. Often, there is some trial and error required to make sure that the confluence of several rules and/or Workers are behaving in an expected manner.

As part of upgrading Page Rules we have separated it into four new products:

  1. Origin Rules
  2. Cache Rules
  3. Configuration Rules
  4. Redirect Rules

This gives users a better understanding into how and when different parts of the Cloudflare stack are activated, reducing the spin-up and debug time. We will also be providing additional visibility in the dashboard for when rules are activated as they go through Cloudflare. As a sneak peek please see:

Our users may take advantage of this strict precedence by chaining the results of one product into another. For example, the output of URL rewrites in Transform Rules will feed into the actions of Cache Rules, and the output of Cache Rules will feed into IP Access Rules, and so on.

In the future, we plan to increase this visibility further to allow for inputs and outputs across the rules products to be observed so that the modifications made on our network can be observed before the rule is even deployed.

Cache Rules. What are they? Are they improved? Let’s find out!

To start, Cache Rules will have all the caching functionality currently available in Page Rules. Users will be able to:

  • Tell Cloudflare to cache an asset or not,
  • Alter how long Cloudflare should cache an asset,
  • Alter how long a browser should cache an asset,
  • Define a custom cache key for an asset,
  • Configure how Cloudflare serves stale, revalidates, or otherwise uses header values to direct cache freshness and content continuity,

And so much more.

Cache Rules are intuitive and work similarly to our other ruleset engine-based products announced today: API or UI conditionals for URL or request headers are evaluated, and if matching, Cloudflare and browser caching options are configured on behalf of the user. For all the different options available, see our Cache Rules documentation.

Under the hood, Cache Rules apply targeted rule applications so that additional rules can be supported per user and across the whole engine. What this means for our users is that by consuming less CPU for rule evaluations, we’re able to support more rules per user. For specifics on how many additional Cache Rules you’ll be able to use, please see the Future of Rules Blog.

How can you use Cache Rules today?

Cache Rules are available today in beta and can be configured via the API, Terraform, or UI in the Caching tab of the dashboard. We welcome you to try the functionality and provide us feedback for how they are working or what additional features you’d like to see via community posts, or however else you generally get our attention ?.

If you have Page Rules implemented for caching on the same path, Cache Rules will take precedence by design. For our more patient users, we plan on releasing a one-click migration tool for Page Rules in the near future.

What’s in store for the future of Cache Rules?

In addition to granular control and increased visibility, the new rules products also opens the door to more complex features that can recommend rules to help customers achieve better cache hit ratios and reduce their egress costs, adding additional caching actions and visibility, so you can see precisely how Cache Rules will alter headers that Cloudflare uses to cache content, and allowing customers to run experiments with different rule configurations and see the outcome firsthand. These possibilities represent the tip of the iceberg for the next iteration of how customers will use rules on Cloudflare.

Try it out!

We look forward to you trying Cache Rules and providing feedback on what you’d like to see us build next.

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Alex Krivit|@ackriv

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