If you don’t know what CDN (content delivery network) is, you may have a lot of questions concerning this technology, and how it influences performance. It’s time to answer the most frequently asked ones and help you to get the general idea of this hosting option.

1. Which performance issues does a CDN solve?

While content delivery networks serve to improve global availability of content and reduce bandwidth, the main problem they solve is latency, e.g. amount of time required for the host server to receive, process and deliver a request for page assets (CSS files, images, JavaScript, etc.). Latency is usually defined by far away a user is from the server, and the total number of resources a web page contains.

For instance, if all your resources are hosted in London, and a user visits your page from New York. In this case, every request has to make a long trip from New York to London and back. If your page contains about 100 objects (which is normal for a usual page), user’s browser will have to make 100 individual requests to the server to retrieve these objects.

As a rule, normal latency stays within 75-140 ms range, but it can get much higher, especially for mobile users who visit a website over 3G network. That can add about 2-3 seconds of loading time, which is pretty much considering the fact that there are many other things which can slow down your pages.

A content delivery network caches static resources in edge servers that are located in PoPs (points of presence) over several regions, or worldwide. That helps to bring resources closer to users and reduce round trip time.

2. Does a CDN help every project?

A CDN can be benefitial for many websites, but not for every site. For instance, if your target audience is located in one region only, a CDN won’t be of much use, and can even hurt performance. Some website developers misbelieve that CDN is a standalone solution. However, you should keep in mind that in E-commerce and SaaS spheres, server-side processing and third-party content can affect performance, and CDN won’t be helpful for that.

3. Are all CDNs the same?

The type of CDN you choose matters a lot. The benefits you reap will depend on the provider you select, as well as the type of content you want your CDN to store, and how far PoPs are placed from your users. To choose the best CDN for your website, you should be aware of where your users are.

Besides, latency also varies from one provider to another. If you compare the differences in latency among different provides, you can realize that it’s dramatic. 3G latency is an aspect that should also be checked separately.

4. Does CDN performance vary?

Recent studies prove that performance even in CDNs from leading providers differs considerably. It depends on the PoPs where servers are located, the quality of servers and many other characteristics.

5. Is CDN efficient for mobile users?

This is a bit tricky question. Yes, CDN are somewhat useful for mobile users, but it’s hard to estimate the cost based on return. Recent studies concerning acceleration of pages for mobile users have shown that:

• Doc loading time was decreased by 10%, while during desktop optimization, 20% improvement was observed.
• Start render time is decreased by just a second, which isn’t very considerable.

Although mobile CDN has some performance gains, they are not particularly significant. However, it doesn’t mean that CDNs are not efficient for mobile. You just need to find a suitable solution that is created specifically for mobile experience: the way how provider tracks users and defines their location matters.

6. Will CDN ensure 100% availability of my website?

Every CDN provider promises about 100% availability, even in case of massive power outages, hardware failures, and network issues, and this guarantee is justified. The thing is that CDNs have automatic mechanisms that track server activity and redirect users to another server, if one (or several) fail. When it comes to “nearly 100% availability”, CDN’s uptime should be specified in customer SLA. Besides, if you want to know the details of a particular provider, you should Google outage availability of company and check what kind of information is shown.

7. Do the most popular websites use a CDN?

Surprisingly, they don’t. Almost 80% of top European E-commerce websites and Top 2.000 E-commerce websites in the USA funciton without help of a CDN. Probably, it’s conditioned by the fact that they can afford infrastructure expansion, and that content delivery networks used to be way more expensive a few years ago. Anyway, today you can easily find more competitively-priced variants on the market.

8. CDNs vs front-end optimization: what helps to deliver pages faster?

In order to reach maximum acceleration, some customers apply the combination of front-end optimization, CDN with application delivery controller and even in-house engineering. As it has been mentioned, CDN boosts performance by bringing resources closer to users: it reduces round trips and accelerates loading process. FEO (front-end optimization) addresses performance at the front end, so pages are loaded more efficiently via browser.

This approach is not a new one – it’s widely used by many companies. It has a significant impact on page metrics starting from the number of requests and finishing by payload. Applying several best practices for website acceleration (compression and keep-alives, CDN, and FEO) for unoptimized desktop website versions can have a very great impact on speed. Compare: if an unoptimized pages loads during 15 seconds, it can load 9 seconds with compression and keep-alives, 7 seconds with compression, keep-ailves and CDN, and only 3 seconds with all above plus FEO. There are many other solutions of using FEO along with a CDN network, including:

1. If you rename files served from CDN automatically, it’ll take much time. With a FEO solution in its place, you can do it automatically and save a lot of time.
2. Use of expires headers is the best solution that can be used. If you add headers, it’s easy, but work with versioning is a headache, especially if you use a CDN. You either need to have someone in charge of CDN purge, of you need to waste a lot of developers’ hours to integrate with CDN’s API. An automated solution will do these things for you and save your time.

9. Can CDNs use SPDY?

Google’s SPDY is a protocol that helps to deliver website content and reduce latency. Experiments with SPDY have shown that it helps to improve delivery time by 27-60% over HTTP.  However, this technology hasn’t been widely adopted by the industry. You can be one of few web-masters to benefit from it: the solution is, in fact, is ultimately useful for end users.

10. Is CDN market competitive today?

In our times, being a website owner is much simpler and more convenient than it used to be. Some several years ago, CDN was affordable for well-off companies (monthly CDN bills were worth thousands dollars!), but today the situation has taken another turn. There’s a wide selection of competitive products offered by innovative companies: they offer advanced CDN technologies that combine perfectly with many other technologies, for instance, real user monitoring (RUM).

11. How to select the right CDN for my project?

This is a question that cannot be answered in a few words. In order to make the choice, you should take into consideration. This is what you should be guided with:

1. First and foremost, define your company’s needs. If you have a more or less well-developed website with pretty much traffic, CDN will be beneficial for you.
2. You focus on E-commerce? Specialize on online or box games? Have a video blog? Choose a CDN option accordingly: it should provide you with sufficient amount of bandwidth and resources and provide additional services tailored for your exact project.
3. Actually, to decide whether you need a CDN or not, you should undestand where your target audience is situated. If you host a local website, you won’t benefit from this technology. However, if your visitors are scattered around the globe (or at least several continents or countries), using CDN will definitely make sense.
4. Pay attention to particular providers. Check guaranteed uptime, customer support characteristics and real users’ reviews. That will help you to understand whether a company can be relied on.