Testing in a High Caching Environment

By Ruby Brown

October 27, 2021


Website optimization and personalization is all about delivering the right experience at the right time to the right user. To do this, your optimization tool needs to be able to recognize context and retrieve the correct experience, and do it quickly. Many websites use CDNs that rely heavily on caching in order to deliver the fastest experience possible. But, most A/B testing tools rely on an SDK at the server in order to execute server-side A/B testing, and these tools either struggle, or cannot execute server-side changes on cached content. This is because a request for a cached web page doesn’t go back to the origin server, meaning it never gets the information to alter the experience. So why is heavy caching a problem for some A/B testing tools, and what should you ask before you select one?

What is Caching?

A website cache is a data storage layer for web content, so that it does not need to be delivered from the server again on every subsequent request. You regularly interact with browser caches and public caches. For example, let’s say you’re shopping on Amazon.com, but you’re not logged in. Even if you leave the site, when you return your items are still in your cart. This is because that information is cached, so it does not need to be retrieved from the server again. Public caches contain site information so that once a page is delivered from the server, it can be stored for faster retrieval by the next visitor. For example, if I am the first visitor to SiteSpect.com in Boston, the page I’m visiting will come from the origin server. But, upon my request, that page gets cached — meaning it’s stored in a local server. Next time someone visits the same page at SiteSpect.com, it will be delivered from the local Boston cache and load faster.

Why Do Some Sites Cache More?

Many websites use a CDN (content delivery network), such as Fastly, Cloudflare, Amazon CloudFront, and others. CDNs work by caching content on various servers closer to users, so that when a user requests a page it can be delivered faster. Cloudflare explains it well,

“Think of a CDN as being like a chain of grocery stores: Instead of going all the way to the farms where food is grown, which could be hundreds of miles away, shoppers go to their local grocery store, which still requires some travel but is much closer. Because grocery stores stock food from faraway farms, grocery shopping takes minutes instead of days. Similarly, CDN caches ‘stock’ the content that appears on the Internet so that webpages load much more quickly.

When a user requests content from a website using a CDN, the CDN fetches that content from an origin server, and then saves a copy of the content for future requests. Cached content remains in the CDN cache as long as users continue to request it.”

CDNs have servers, or PoPs (points of presence) around the world so that users can access information faster.

How Does My CDN Impact A/B Testing and Optimization?

Most optimization tools rely on an SDK for server-side A/B testing. This means that when a user requests a page, that request goes to the origin server, and only there, does an SDK (software development kit) placed by the optimization tool help alter the request appropriately. When you’re applying server-side changes, this method requires that trip back to the server in order to execute. But, when most of your content is cached, that trip back to the server never happens. Instead, content comes from the CDN cache. That means that server-side A/B testing is either impossible, or requires heavy development and workarounds to happen for most tools.

How Does SiteSpect Manage Server-Side A/B Testing in a High Caching Environment?

While SiteSpect does have an SDK option to execute server-side A/B testing, it also sits in the flow of traffic — just like your CDN. Unlike other optimization tools, SiteSpect can integrate with many CDNs and work in conjunction with them so that you can still optimize even if a large percentage of your website is cached. Depending on your unique workflow, SiteSpect will design and implement a custom solution so that you can still execute all of your optimization requirements — something other tools simply can’t do.

Does SiteSpect Work with My CDN?

Learn about whether SiteSpect integrates with your CDN by visiting our Third Party Integrations page.

To learn more about SiteSpect, visit our website.




Ruby Brown

Ruby Brown

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