How to Choose a CDN

There has been a surge in the number of CDN services and the use of CDN services in recent months. In this article, we will consider why a certain provider might be a good fit.

Whole site CDN / static website

Whereas CDNs are conventionally used to host only static assets (CSS, Javascript, fonts and images), some informational websites, where every user sees the same page, can be served entirely from a CDN. In this case, you point your domain at the CDN service and the CDN acts as a reverse proxy for your website, much like Cloudflare and Incapsula, but without the bells and whistles. The CDN caches the whole website in different locations, meaning that your website load time is excellent. When you update content on the website, such as publishing a new article, you clear the CDN to reset the caches.

This type of CDN is known as a Static Site CDN, and tends to include a number of features to make it easy to host static content in different locations. If your website is based on Javascript, you can also consider pre-rendering it to improve speed and help Google to find your content.

Whereas static sites, that is, sites with just HTML content, were popular in the ’90s, they are less common today. Therefore, you may need software to generate one for you, using your existing website. Such static site generators are, incidentally, also surging in popularity. Specialist CDNs for static sites, such as Netlify, include built-in tools, although plenty of open source tools are available for different programming languages. Plugins are also available for WordPress.

You can, generally, use almost any CDN for your static site. However, you should consider the reach of the CDN (as always, they should be present where your users are). The features offered by the CDN are also especially important, as, for example, you may want to use your own SSL certificate and control cache expiry times. Aside from Netlify, we have found KeyCDN to be an excellent choice to maximise the use of modern software innovations as well as an extensive network and reasonable prices.

Network coverage

Your CDN should, first and foremost, be present where your users are. Cheap CDNs, like MaxCDN, generally cover locations where hosting is cheaper, to keep costs low. If all of your users are based in the EU and US, this may be ideal, but bear in mind that users (and potentially search rankings) outside these areas – that is, primarily, Australia and Asia, will be limited. Consider whether, for a small percentage cost difference, it is worth using a CDN with better coverage.

Equally, many of the “big name” CDNs, like Edgecast and Akamai, have points of presence in a very large number of locations. The benefit it touted as the content being as close as possible to the user. This is, potentially, correct. However, bear in mind that if the POP does not have your content in its cache, which is more likely on a larger network, it has to fetch it, usually from your server, before delivering it. This is far from ideal. To counterbalance this, some such CDNs offer their own storage facility, that should be considered alongside the CDN offer.

Neither Akamai not Edgecast (now Verizon) sell directly to small businesses. Akamai’s CDN is available via Rackspace and Edgecast is available via Speedy Rails. These resellers offer access to the same network although the level of control is sometimes limited, and in particular, there may be significant additional costs for certain features that are free with smaller CDNs.

Features

Features should be considered carefully. There are numerous software innovations that, alongside good network coverage, are a significant benefit:

1. HTTP/2
   To vastly simplify this evolution in Internet standards, if your server or CDN supports HTTP/2, all modern web browsers, including mobile, will be able to download more than one resource using the same connection. Since there is some overhead at both ends for each connection, HTTP/2 can make a surprising difference to the speed of your website.
2. Compression
   Conventionally, we hear that HTTP compression, such as gzip, makes websites faster. In reality, one of the reasons why this is not always the case, is that the server has to compress the content before sending it. If the compressed content is not cached, which it usually isn’t, and the website is busy, it can add noticeable CPU overhead to the server, slowing down the website overall. A CDN that implements compression for you is giving you access to compression for nothing.
3. Minification
   CSS, HTML and Javascript can be minified, that is, most of the white space can be removed without impacting the functionality of the files. Consider this carefully, as the implementation of a given minification algorithm may break your specific content. CSS is generally safe, Javascript and HTML can be less safe. Much like compression, offloading this to the CDN saves your server some of its resources.
4. Expiry Times
   Some CDNs let you specify your own expiry times, and specify headers too. Fine-grained control over the amount of time that browsers hold on to CDN-delivered content, and how long the CDN itself holds on to the content, can be extremely useful to ensure that your website it as fast as it can be, without impacting functionality.
5. HTTPS
   Whereas most CDNs let you use HTTPS, some are stuck in the dark ages, when there was a cost associated with it. These are generally the larger CDN networks and also Fastly. For these, you may not be able to use HTTPS with your own domain, due to certificate limitations, or may not be able to use an EV SSL certificate, if you would like to, due to the cost involved in setting it up and maintaining it. This is likely to change in the near future, as standards such as SNI are implemented more widely.

Posted on June 14, 2017 at 9:56 am in Business BenefitsHow toTutorials

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