Those who have haven’t heard of Content Delivery Network (CDN) , here is the summation along with an example :
“Content Delivery Network is a collection of network for offloading web traffic with usually decision based on geographic location”
Example : You are running a website hosted in London. Your CDN providers has servers dispersed globally ,including New York. Now if the visitors are requesting the web resource from New York itself , they would get a response from CDN server based in New York rather then request going all the way down to London.
I wont be discussing the internals of CDN here as it out of scope of the current article. But still you can refer below urls (or google it yourself):
While going for a CDN vendor here are the 5 things which are important and people usually miss out :
1. Full Page Caching
Their are some of the providers who provide CDN services which is limited to static files ie. js,css and image files for a very meager sum or for free. If you are using it for free , it sounds all right and may be your images will get load faster.
But in a scenario where you have content rich page , what is the use of delivering static files only through CDN as the whole call for the url would get called to origin for each and every visitor inducing a latency. Caching static files on CDN is a good practice and caching static files along with whole HTML is a much better practice.
2. Adaptive response
Most of the Internet bloggers and portal owners went into panic, after google released its new search engine update, making responsive and mobile friendly page must for better rankings. It meant people running different portal for mobile and handheld device, had to convert the legacy design to responsive one. But along with responsive, to achieve performance and decrease page size many went for responsive+adaptive method.
Make sure if you are basing a decision for enterprise as a part of technology team or consultant it should be a must. Ideally the provider should agree to maintain multiple cache copies based on device type or geographic locations if the backend code is adaptive. I have seen some of the providers ,who commit to an adaptive response but don’t cache the response bypassing the response directly to origin.
3. Flexible Dashboard
Sometimes it is required to set the caching at a very granular level . For an example their is an NFL tournament going on and we need to update the score every 30 second. We don’t want to our visitors to see the old scores, do we ? Dashboard should have ideally the flexibility of setting caching interval on url basis , with an option specifying regex.
Also features ie. Cache purge , Logs analysis , WAF , Performance meter, billing metrics , geographic visitors segreagration etc , compromised a part of an ideal package,
4. Origin failover or “Keep serving stale option”
What would happen if origin goes down ? CDN would keep on serving the data until cache expiry time. If a story has a caching time of 5 minutes, CDN would keep on serving it for that time.
In case you have a disaster recovery site or a server running in redundancy. You could ask for feature known as origin failover , which would automatically shift the incoming request to secondary location or origin in case primary goes down.
Some of them also provide feature , where they keep on serving last cached data (stale data) irrespective of caching expiry until CDN POPs are being able to communicate to the origin.
5. Cedexis rating and reviews
Cedexis has done a wonderful job of segregating and benchmarking CDN and ISP networks globally. I wont say it would be 100% accurate, as the benchmark data is usually a minor percentage of a sample, but it gives a perfect comparative picture of providers.
