How to Evaluate Caching and Performance When Choosing a CDN Service

When choosing a CDN service, first determine which types of content on your site need acceleration: caching capabilities matter for static files such as images, stylesheets, and JavaScript, while request routing, secure connections, and protecting the origin server are important for personalized pages. The right choice depends not only on the number of edge locations, but also on how your content is updated and where your visitors connect from.

What problem does a CDN service solve?

Instead of sending content directly from the origin server to every visitor, a CDN delivers it through intermediary servers located in different network locations. When a visitor requests a file, an appropriate edge location can respond without contacting the origin server if it has a cached copy of that file. As a result, the number of requests reaching the origin server may decrease, especially for large images, stylesheets, JavaScript packages, and downloadable files.

This setup does not automatically speed up every request. A shopping cart page containing session information, an administration panel, or a user-specific account screen generally should not be cached in the same way for everyone. If static files make up most of your workload, focus on long-term, controlled caching support when choosing a CDN service. If content changes according to the user or session, it becomes more important for the CDN to forward those requests securely to the origin server and for you to be able to manage cache exceptions.

Evaluating cache behavior according to the workload

Caching means keeping a file or response at an edge location for a specific period. How that period is determined may be affected by response headers such as Cache-Control, CDN rules, and the file’s URL. The approach of “cache every type of content” is not a safe choice; showing a stale response to a user can create a more serious content problem than the benefit of saving a few milliseconds.

If you can version file names and publish a new URL after a change, a long cache duration may make sense for static assets. By contrast, frequently changing campaign images or news content require a short duration, controlled invalidation, or an explicit purge operation. Verify in advance whether the CDN allows you to purge a single file, a specific directory, or the relevant cache group, and how this process works with that provider.

For example, suppose, hypothetically, that a documentation site publishes large PDF files and images that rarely change, while displaying personal information on membership pages. In this case, a CDN that offers a long cache duration and file-versioning support would be a suitable candidate; membership URLs must be excluded from the cache. If the same site overwrites the same files every day, it is more appropriate to evaluate purge speed and when the old file is dropped rather than looking only at the number of edge locations.

How should you compare a CDN service during initial use?

Start the comparison with your own content map before looking at the provider’s feature list. Divide files into three groups: publicly accessible static files, frequently changing public content, and responses containing session information or personalization. For the first group, cache duration, file versioning, and domain configuration are the main considerations. For the second group, examine purge and refresh options. For the third group, the default cache behavior must be safe, and exception rules must be clearly manageable.

Next, evaluate the service with a small test domain or a low-risk static file. Open the file through the CDN and inspect the response headers for provider-specific information showing whether it was served from the cache, its age, and records indicating the origin server. The first request may be expected to go to the origin server, while a subsequent identical request may be served from the edge location; however, header names and behavior vary by provider. If the result does not confirm this, examine the file’s response headers, query parameters, and the CDN rule priority.

Change the content of a file in a controlled manner and open the same URL again. If the old content is still displayed, use the CDN’s purge or revalidation mechanism; if file versioning is available, try again with a new file name. If the new content appears, the test is successful, but this does not mean that personalized pages can also be safely cached. The acceptance criterion is that the correct content is delivered for the expected file type and that the rules affect only the intended response.

DNS, HTTPS, and origin server conditions

Using a CDN generally requires the domain’s DNS records to be directed in the format expected by the provider and the HTTPS certificate to work on the correct domain. The details of these steps depend on the provider, the DNS management system in use, and the existing certificate setup. Before making changes, record the existing DNS records and the origin server address; during testing, change only the relevant subdomain so that returning to the previous setup remains easy.

If you are considering restricting access on the origin server so that it trusts only traffic from the CDN, do not add a rule before verifying the network addresses used by the provider and its update method. In some applications, reading the real visitor IP from headers also depends on the configuration. If application logs no longer show the expected client information, do not interpret this as proof that the CDN is automatically malfunctioning; check the relevant headers and the web server’s trusted-proxy settings.

Practical decision criteria for choosing

• Site focused on static files: If images and scripts dominate, prioritize the ability to monitor cache headers, file versioning, and purge options; an extensive rule set for dynamic requests may not be necessary.
• Frequently updated content: If it is critical to know how long old content may remain visible after publication, test the purge scope and revalidation behavior; do not choose an option solely because it offers a long cache duration.
• Session-based application: If you have shopping cart, account, or administration screens, first verify cache-exclusion rules in a small test. If a rule is unclear, a safer starting point is not to place personalized responses in the CDN cache.

After completing this evaluation, review your domain’s DNS management and the CDN’s setup documentation together. You can look at the İyibirNet home page to review general hosting and infrastructure options; however, make the CDN decision based on your own content types and update process.