Proven Drupal Caching Best Practices for Experienced Developers

As your Drupal site expands, both in complexity and traffic, server resources can quickly become overburdened, slowing down your site’s performance and negatively impacting the user experience. Caching is the solution to avoid these issues. 

But effective Drupal caching isn’t as simple as flipping a switch. It’s a multi-layered system that can transform a sluggish site into a high-speed, responsive platform.

In this article, we’ll break down the finer points of Drupal caching, exploring advanced techniques and strategies to optimize performance. With the right approach and tools – like those offered by Pantheon – your site can deliver a fast, smooth experience even under heavy loads!

The Basics of Drupal Caching: Layered Caching Architecture

Drupal has a sophisticated layered caching architecture designed to speed up your site by caching content at multiple levels. Let’s break it down:

Application-Level Caching

Drupal has built-in application-level caching that is active by default. It stores internal data like entities, fields, menus and other system components. The goal is to reduce the time spent fetching this data repeatedly. 

For example, the Entity Cache stores rendered entities such as nodes, taxonomy terms and users. By reducing database queries, entity caching improves performance, especially on content-heavy sites. It’s part of Drupal 10’s core, giving you this advantage right out of the box.

Component-Level Caching

Moving deeper, component-level caching focuses on user-facing elements like blocks, panels and views. These are typically disabled by default but can be enabled for components that remain static across different pages, boosting performance when configured correctly. For example:

• Block cache allows caching for static content blocks, meaning Drupal doesn’t have to rebuild these blocks every time a page is loaded. It's an ideal solution for elements like a footer or sidebar that stay consistent across multiple pages.
• Views cache, the powerful query builder in Drupal, doesn’t cache its data by default. However, with the Views Content Cache module, you can set up view caching with automatic cache invalidation. This is particularly helpful for dynamic content on frequently updated sites.
• Rendered output cache saves the final HTML output of rendered entities or components, serving cached versions of the content to avoid regenerating the markup repeatedly.

Page-Level Caching

At the top layer, page-level caching stores and serves entire HTML pages, particularly for anonymous users. This type of caching is highly efficient, as it prevents the execution of PHP or database queries when serving content. For instance:

• Page cache stores fully rendered HTML pages for anonymous visitors, so subsequent requests for the same page deliver cached content without regenerating it.
• Dynamic page cache goes beyond the basic page cache. This cache optimizes performance for authenticated users by caching most of the page while regenerating only the dynamic sections that can’t be cached.

The Main External Caching Systems in Drupal

In addition to Drupal’s internal caching system, you can supercharge your site’s performance by integrating external caching solutions like:

CDNs store cached copies of your website at various edge locations around the globe. This reduces the physical distance between your users and the content they’re accessing, drastically cuts down latency and speeds up page load times. Think of it as placing a copy of your site’s assets in multiple digital “warehouses” worldwide, making delivery as fast as possible for every visitor.

Reverse Proxy Caches

A reverse proxy cache sits in front of your web server, caching generated pages so they can be delivered faster without hitting the server again. Popular reverse proxy solutions include:

• Varnish: Known for its high performance, Varnish is often used with Drupal to cache entire pages for anonymous users, offloading much of the page generation process from your web server.
• Nginx: Capable of reverse proxy caching, helping improve response times by caching the web content and serving it directly to users.

These systems are excellent at handling high-traffic loads and ensuring your users get a quick response, especially for pages that don’t change frequently.

PHP Opcode Caches

PHP opcode caching ensures that PHP code doesn’t need to be parsed and recompiled with each request. Instead, it caches the compiled code so subsequent requests are served faster. One of the most common options is APC (Alternative PHP Cache), which can significantly reduce server resource usage by eliminating the need to reprocess code on every page load.

Object Caches

Object caching stores cached data in memory, reducing the need for repeated database queries or external data retrieval. Redis is a frequently used object cache with Drupal, storing data objects in memory to speed up retrieval and lighten the load on your database. This is particularly useful for large-scale sites with complex data structures that are queried often.

Mastering the Drupal Cache API

The Drupal Cache API is a powerful tool that allows developers to store and reuse previously computed data, speeding up future requests and enhancing site performance. It's a layered system designed to manage caching across different components and it plays an important role in reducing server load while keeping your site responsive.

Cacheability Metadata

One of the best features of Drupal’s Cache API is its cacheability metadata, which lets developers control how and when data is cached through the Render API. Here’s how the metadata breaks down:

• Cache tags enable fine-grained control over cache invalidation. For example, if you publish a new blog post, Drupal can automatically invalidate the cache entries related to your content list so that it reflects the latest update.
• Cache contexts define variations of cache entries based on specific contexts, such as user roles, languages, or geographic location. This ensures users see the right version of content based on their unique situation, like showing different product prices to users in different countries.
• Cache max-age sets how long an item should stay in cache before it’s refreshed. For example, you can set short max-ages for highly dynamic content or longer max-ages for static content, helping balance performance and freshness.

These metadata elements can “bubble up” within a render array, meaning that cacheability requirements of nested elements are combined and respected at higher levels of the rendering process.

Cache Bins

Drupal also organizes cached data into cache bins, which serve as storage containers for cached items. This binning system allows for faster, more efficient lookups and developers can interact with cache bins programmatically via the cache backend service. For custom caching needs, you can use different bins to separate various types of data, making your cache more structured and easier to manage.

Cache Invalidation

Cache invalidation means that your site’s cached content stays up to date. Using cache tags, Drupal automatically invalidates cache entries when related data changes. For example, updating a product description or deleting a user will trigger invalidation, preventing stale data from being served. This automation ensures that your users always receive fresh content without you having to manage cache clearing manually.

Drupal Caching Strategies for Anonymous and Authenticated Users User Types

Caching for Anonymous Users

For anonymous users, Drupal leans on the Page Cache module to deliver a static, full-page caching solution. This module stores entire HTML pages as files, serving them to subsequent anonymous visitors without invoking Drupal’s bootstrap process or executing PHP code. This drastically reduces load times and server strain, making it ideal for high-traffic, read-heavy sites.

To verify if page caching is working for anonymous users, you can inspect the headers of a page request. Look for the x-drupal-cache: HIT header. If it shows MISS on the first request, simply refresh the page and you should see HIT on subsequent visits, indicating that caching is now in play.

Caching for Authenticated Users

Authenticated users present a greater challenge because they often see personalized, dynamic content that can’t simply be cached as static HTML. Drupal’s Dynamic Page Cache module intelligently caches parts of the page that are static while keeping dynamic elements – such as personalized blocks or user-specific content – intact. It allows Drupal to serve cached versions of the page while still tailoring certain elements to each user.

To check if dynamic page caching is working for authenticated users, look for the x-drupal-dynamic-cache: HIT header in the request. Similar to the Page Cache module, you’ll see MISS on the first load, but it should switch to HIT after refreshing the page.

Boosting Drupal Performance With Pantheon

Pantheon – our WebOps hosting platform – is designed with Drupal performance in mind, offering built-in caching and optimization features to keep your site running at peak speed.

Global CDN Page Caching

Pantheon’s Global CDN, powered by Fastly, means your site is served quickly from one of over 40+ global points of presence (POPs). This CDN caches assets like CSS, images and entire web pages (including HTML). 

With Varnish built-in, the CDN delivers repeat page views directly from its cache, bypassing the need for rendering from the CMS. This dramatically reduces page load times, especially for high-traffic sites and ensures your users are getting a lightning-fast experience no matter where they are.

Pantheon Advanced Page Cache

To further integrate caching with Drupal, Pantheon provides the Advanced Page Cache module, which works easily with the Global CDN. This module uses Drupal's cacheability metadata to intelligently clear specific cached pages when content is updated. Through surrogate key technology, cached responses are tagged with data identifiers like author or category, allowing only the necessary parts of the cache to be refreshed.

Additionally, developers have more control over Varnish features through the Advanced Page Cache module and Pantheon’s dashboard. For instance, you can configure the NO_CACHE cookie to bypass the cache for users like admins, who need to preview changes without affecting cached pages.

Redis Object Cache

For dynamic pages and logged-in users, Pantheon offers a Redis-based Object Cache as an add-on. Redis caches Drupal application objects and database queries in memory, eliminating the delays of disk access. This means that even dynamic content can be served almost instantly, greatly improving performance for authenticated users and more complex site interactions.

One-Click Development Environments

Pantheon also makes it easy for developers to fine-tune their caching and performance strategies with one-click development environments. With a single click, you can spin up a Dev, Test, or Live environment to test out different caching configurations or other performance improvements. Even better, Pantheon’s Multidev feature allows you to create unlimited, cloud-based environments to work on different features or optimizations without impacting the live site.

Supercharge Your Drupal Site With Pantheon Today

To truly master Drupal caching, experienced developers know that it's not enough to stick to the basics. Advanced techniques and the right tools must become a part of your performance optimization workflow to make sure your site is not only fast but also scalable and reliable.

As the fastest Drupal hosting on the planet, Pantheon offers everything you need to push your site’s performance to the limit. From Global CDN page caching to Advanced Page Cache and Redis, Pantheon provides a powerful suite of tools that make implementing caching best practices effortless.

With Pantheon, your Drupal site will deliver a smooth and efficient experience to users across the globe. Try Pantheon for free today and explore its advanced Drupal solutions!