Amazon’s CloudFront CDN

Amazon’s previously-announced CDN service is now live. It’s called CloudFront. It was announced on the Amazon Web Services blog, and discussed in a blog post by Amazon’s CTO. The RightScale blog has a deeper look, too.

How CloudFront Works

Basically, to use the CloudFront CDN, you drop your static objects (your static HTML, images, JavaScript libraries, etc.) into an S3 bucket. (A bucket is essentially the conceptual equivalent of a folder.) Then, you register that bucket with CloudFront. Once you’ve done this, you get back a hostname that you use for as the base of the URL to your static objects. The hostname looks to be a hash in the cloudfront.net domain; I expect CloudFront customers will normally create a CNAME (alias) in their own domain that points to it.

The tasks use Amazon API calls, but like every other useful bit of AWS functionality, there are tools out there that can make it point-and-click, so this can readily be CDN for Dummies. There’s no content “publication”, just making sure that the URLs for your static content point to Amazon. Intelligently-designed sites already have static content segregated onto its own hostname, so it’s a simple switch for them; for everyone else, it’s just some text editing, and it’s the same method as just about every other CDN for the better part of the last decade.

In short, you’re basically using S3 as the origin server. The actual delivery is through one of 14 edge locations — in the particular case of these locations, a limited footprint, but not a bad one in these days of the megaPOP CDN.

How Pricing Works

Pricing for the service is a little more complex to understand. If your content is being served from the edge, it’s priced similarly to S3 data transfers (same price at 10 TB or less, and 1 cent less for higher tiers). However, before your content can get served off the edge, it has to get there. So if the edge has to go back to the origin to get the content (i.e., the content is not in cache or has expired from cache), you’ll also incur a normal S3 charge.

You can think of this as being similar to the way that Akamai charged a few years ago — you’d pay a bandwidth fee for delivering content to users, but you’d also pay something called an “administrative bandwidth fee”, which was charged for edge servers fetching from the origin. That essentially penalized you when there was a cache miss. On a big commercial CDN like Akamai, customers reasonably felt this was sort of unfair, competitors like Mirror Image hit back by not charging those fees, and by and large the fee disappeared from the market.

It makes sense for Amazon to charge for having to go back to the (S3) origin, though, because the open-to-all-comers nature of CloudFront means that they would naturally have a ton of customers who have long-tail content and therefore very low cache hit ratios. On a practical basis, however, quite a few people who try out CloudFront will probably discover that the cache miss ratio for their content is too high; since a cache miss also confers no performance benefit, the higher delivery cost won’t make sense, and they’ll go back to just using S3 itself for static delivery. In other words, the pricing scheme will make customers self-regulate, over time.

Performance and CDN Server Misdirection

Some starting fodder for the performance-minded: My preliminary testing shows that Amazon’s accuracy in choosing an appropriate node can be extremely poor. I’ve noted previously that the nameserver is the location reference, and so the CDN’s content-routing task is to choose a content server close to that location (which will also hopefully be close to the end-user).

I live in suburban DC. I tested using cdn.wolfire.com (a publicly-cited CloudFront customer), and checked some other CloudFront customers as well to make sure it wasn’t a domain-specific aberration. My local friend on Verizon FIOS, using a local DC nameserver, gets Amazon’s node in Northern Virginia (suburban DC), certainly the closest node to us. Using the UltraDNS nameserver in the New York City area, I also get the NoVa node — but from the perspective of that nameserver, Amazon’s Newark node should actually be closer. Using the OpenDNS nameserver in NoVa, Amazon tries to send me to its CDN node in Palo Alto (near San Francisco) — not even close. My ISP, MegaPath, has a local nameserver in DC; using that, Amazon sends me to Los Angeles.

That’s a serious set of errors. By ping time, the correct, NoVa node is a mere 5 ms away from me. The LA node is 71 ms from me. Palo Alto is even worse, at 81 ms. Both of those times are considerably worse than pure cross-country latency across a decent backbone. My ping to the test site’s origin (www.wolfire.com) is only 30 ms, making the CDN latency more than twice as high.

However, I have a certain degree of faith: Over time, Amazon has clearly illustrated that they learn from their mistakes, they fix them, and they improve on their products. I assume they’ll figure out proper redirection in time.

What It Means for the Market

Competitively, it seems like Rackspace’s Cloud Files plus Limelight may turn out to be the stronger offering. The price of Rackspace/Limelight is slightly higher, but apparently there’s no origin retrieval charge, and Limelight has a broader footprint and therefore probably better global performance (although there are many things that go into CDN performance beyond footprint). And while anyone can use CloudFront for the teensiest bit of delivery, the practical reality is that they’re not going to — the pricing scheme will make that irrational.

Some people will undoubtedly excitedly hype CloudFront as a game-changer. It’s not. It’s certainly yet another step towards having ubiquitous edge delivery of all popular static content, and the prices are attractive at low to moderate volumes, but high-volume customers can and will get steeper discounts from established players with bigger footprints and a richer feature set. It’s a logical move on Amazon’s part, and a useful product that’s going to find a large audience, but it’s not going to majorly shake up the CDN industry, other than to accelerate the doom of small undifferentiated providers who were already well on their way to rolling into the fiery pit of market irrelevance and insolvency.

(I can’t write a deeper market analysis on my blog. If you’re a Gartner client and want to know more, make an inquiry and I’d be happy to discuss it.)

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Posted on November 18, 2008, in Infrastructure and tagged , , , , , , . Bookmark the permalink. 3 Comments.

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