Earlier this month, Google announced an Alpha Cloud Content Delivery Network (CDN) offering. The service aims to provide static content closer to end users by caching content in Google’s globally distributed edge caches. Google provides many more edge caches than it does data centers and as a result content can be provided quicker than making full round trip requests to a Google data center. In total, Google provides over 70 Edge points of presence which will help address customer CDN needs.
In order to use Cloud CDN, you must use Google’s Compute Engine HTTP(s) load balancers on your instances. Enabling an HTTP(S) load balancer is achieved through a simple command.
In a recent post, Google explains the mechanics of the service in the following way: “When a user requests content from your site, that request passes through network locations at the edges of Google's network, usually far closer to the user than your actual instances. The first time that content is requested, the edge cache sees that it can't fulfill the request and forwards the request on to your instances. Your instances respond back to the edge cache, and the cache immediately forwards the content to the user while also storing it for future requests. For subsequent requests for the same content that pass through the same edge cache, the cache responds directly to the user, shortening the round trip time and saving your instances the overhead of processing the request.”
The following image illustrates how Google leverages Edge point of presence caches to improve responsiveness.
Image Source: https://cloud.google.com/compute/docs/load-balancing/http/cdn
Once the CDN service has been enabled, caching will automatically occur for all cacheable content. Cacheable content is typically defined by requests made through an HTTP GET request. The service will respect explicit Cache-Control headers taking into account for expiration or make age headers. Some responses will not be cached including ones that include Set-Cookie headers, message bodies that exceed 4 mb in size or where caching has been explicitly disabled through no-cache directives. A complete list of cached rules can be found in Google’s documentation.
Google has traditionally partnered with 3rd parties in order to speed up the delivery of content to consumers. These partnerships include Akamai, Cloudflare, Fastly, Level 3 Communications and Highwinds.
Other cloud providers also have CDN offerings including Amazon’s CloudFront and Microsoft’s Azure CDN. Google will also see competition from Akamai, one of the aforementioned partners, who has approximately 16.3% CDN market share of the Alexa top 1 million sites.