How to Evaluate Content and Caching When Choosing a CDN Service

CDN service delivers cacheable content from your website, such as images, style files, JavaScript files, and some downloadable files, through servers located closer to visitors. This means the origin server does not have to handle every request on its own. However, a CDN does not automatically speed up database queries or personalized session operations; making the right choice depends on distinguishing which content is static and which is dynamic.

How does a CDN service provide its benefits?

A CDN places distributed cache servers between the website’s origin server and its visitors. When a visitor requests a file, the system serves it from an appropriate edge server if an up-to-date copy has already been stored there. If no copy exists, the request goes to the origin server, the file is retrieved, and, depending on the rules, it is cached for subsequent requests. This structure can reduce the number of requests sent to the origin server, especially for large and frequently requested files.

The first decision is to determine what type of content makes up the site’s workload. If most visitors download the same images and CSS files, a CDN is a logical candidate because the same file does not need to be fetched repeatedly from the origin server as long as it has not changed. By contrast, if each request generates a user account, shopping cart, or current inventory status, caching those responses may be inappropriate for data privacy and freshness. In that case, the CDN can be used for static files while dynamic application traffic is left to the origin server.

Why does the difference between static and dynamic content matter?

Static content is a file that provides mostly the same data to most users when the same URL is requested. A logo, product image, font, style file, browser script, or publicly available PDF may fall into this category. Dynamic content changes according to the logged-in user, location, shopping cart, or current state of the database. Even if a page’s HTML structure appears fixed, a user-specific section within it may be dynamic.

This is where the second decision chain arises: if content is the same for everyone and changes infrequently, a long cache duration may be considered; if content is updated frequently but is still served identically to everyone, a shorter duration or versioned filenames may be preferred; if content varies by user, it should be kept outside the CDN cache, or only safe, shared sections should be cached. Extending the duration unnecessarily can cause outdated files to be shown, while shortening it unnecessarily can reduce the load advantage the CDN provides to the origin server.

Cache duration and the update method

Cache duration determines how long a file is considered valid on an edge server. When a file is updated, there are two common approaches: remove old copies through a purge operation in the CDN panel, or change the file’s URL by adding version information. The second approach can be more predictable during the publishing process because it separates the old and new files; however, the HTML file must reference the new URL. Since the provider’s interpretation of headers and purging behavior may vary, this detail should be verified when choosing a service.

Which features should be examined before choosing a CDN service?

First, examine how the CDN works with the domain name used by your site, its HTTPS setup, and its origin server. Some services require DNS routing, while others require a particular domain name or a reverse-proxy configuration. Where the TLS certificate terminates, how the connection to the origin server is protected, and the extent to which HTTP cache headers are honored may vary by provider. Therefore, looking only at the number of server locations is not enough.

• Cache rules: Check which content can be stored according to the URL, file type, or response headers, and how dynamic responses are excluded.
• Purging behavior: Determine whether you can purge only one changed file or a broader area; a broad purge may place many simultaneous new requests on the origin server.
• Monitoring tools: Being able to see cache hits, origin-server requests, and error status in response headers lets you investigate problems using evidence instead of assumptions.
• Origin-server limits: A CDN’s protection or caching feature does not automatically increase the application’s capacity; the origin server still handles dynamic requests and responses that are not cached.

Suppose images on a news website are published under the same URLs and editors change images several times during the day. Using a CDN for the images may be appropriate; however, if it is unacceptable for the old image to remain visible for a long time, a short cache duration or a publishing workflow that changes the file URL should be selected. Comment submission, membership, and administration screens should not be included in the same cache rule because they are user-specific.

How can you evaluate the initial setup safely?

Before placing an important static file behind the CDN, first note its URL, response status, and content version. Then create a rule for only a low-risk file type; caching the entire domain at once can broaden the impact of an incorrect rule. During testing, open the Network section of the browser’s developer tools and inspect the same file through a new request. A successful response, the file arriving with the correct content, and the cache header showing the expected state are the basic acceptance criteria.

After changing the file, test the same URL again. If the new content does not appear, first compare the cache duration in the CDN rule and the result of the purge, and then compare the cache headers sent by the origin server. Purge only the cache for the tested file and make the same request again; if the result improves, the problem is likely the validity period of the old copy. If it does not improve, check that the file has actually changed on the origin server and that the domain routing to the CDN is correct. Recording the previous rule and its values before making a change makes it easier to roll back if the result is unexpected.

When evaluating whether a CDN is suitable for your site, first determine the share of traffic made up by static files, then the sensitivity of dynamic responses, and finally the update frequency. During this evaluation, you can also review the related hosting and server information on İyibirNet; however, verify your technical decision against your own domain structure and the provider’s documentation.