One big thing they do is cache static assets for you at their edge locations. The majority of the bandwidth costs imposed by static images, CSS and JavaScript (assuming appropriate cache settings) should be offloaded onto CloudFlare once you set it up.
This is what any CDN does, including CloudFront (although supposedly CloudFront's cache hit ration is fairly low). The specific issue at hand is in what way CloudFlare (a CDN) saved more money than CloudFront (another CDN): neither "it typically saves money" (eastdakota's answer) nor "it is a CDN" (effectively your answer) answer that question: these are both nothing more than tautologies restated from the initial question, and do not help someone attempting to compare these two services. (Personally, I use CDNetworks, after having used EdgeCast for a while and evaluating Akamai for my use case; I personally see no reason why I would use CloudFlare, but am always curious.) (Is the issue simply that CloudFront is so expensive that you don't feel you are saving much money? Hence my question then about negotiating with a larger CDN, such as any of the ones I was working with.)
Well, yeah, but my point is that CloudFront does this too. The quote I selected made it sound like CloudFlare reduces bandwidth usage by 70% in comparison to CloudFront. So I'm curious how that works.
$3k/mo buys you a lot of bandwidth, though; even at CloudFront's somewhat-high-for-a-CDN pricing, that's 30TB of bandwidth; to see a 95% reduction in your hosting costs over CloudFront with $3k/mo unmetered bandwidth you'd have to be pushing 1.8PB of data. (edit: I originally said 600TB, but I had done the math wrong for the later discount brackets.)
Even if you were down at the $200/mo plan, that's 45TB/mo before you get to the "95% less expensive" point; I have tens of millions of users worldwide downloading megabytes of packages from me (while the Cydia ecosystem has tons of things much larger, I don't host those: I just have the core package), and I don't often go above 45TB/mo.
Is the idea here that CloudFlare is seriously giving you ludicrously unlimited amounts of bandwidth (and will not give you any crap about it) with a high cache-hit ratio even at their $20/mo plan? If so, I'm going to have to run some insane experiments with their service ;P. (Part of me isn't certain that I want them to hate me that much, though ;P.)
(edit:) Ok, I looked into this some, and this argument ("they don't charge for bandwidth") is just as false as one would expect given that it isn't feasible of them to price that way ;P. Their terms of service makes it very clear that they are only designed for HTML, and that "caching of a disproportionate percentage of pictures, movies, audio files, or other non-HTML content, is prohibited" <- yes, even "pictures".
With this glaring restriction, there is really no way I can imagine any reasonably-normal company getting a 95% reduction in hosting costs over another CDN, even CloudFront: if you are pushing tens of terabytes of mostly-HTML content a month, you are doing something insanely awesome (and we've probably all heard of you ;P).
If it's web content, go right ahead. We have many very large sites using the free plan. From your use, it sounds like you're using a CDN for file distribution (i.e., sending out large package files), not traditional web content. CloudFlare isn't designed for that use case. We're also not setup for streaming content (e.g., if you're running a streaming server for video). In both those cases, you're likely better with a traditional CDN. However, if you're using us for traditional web content, there are no bandwidth caps even on the free plan.
We're running some e-commerce sites with 8-20k items through the $20/month plans and have never heard a complaint from Cloudflare. That said, any sites we 'care' about are running on their business or enterprise levels which are much higher than $20/month :P.
Probably you won't see this reply, but if you do... we move a decent amount, but not a crazy amount. In the last 30 days it was around 3TB total (through Cloudflare... we only saw about 2/3 of that).
Cloudflare pays for this. They've been sponsoring cdnjs for around a year now.
As for the security of our system, all javascript files are verified against official sources before going on the cdn. Additionally, we have many library maintainers submitting updates to their own libraries.
Beyond that the only question remaining is our personal integrity. Like any relationship with a third party, you're going to have to decide whether trusting us is an acceptable level of risk. If past performance is any indication of integrity, we have had no security incidents since we began in January 2011.
I assume you are the creator of cdnjs - what are your relation with cloudflare beyond just the sponsorship? Are you working for them? Do you advise them?
I'm wondering what is the performance increase delivered by cloudflare. I've heard many mixed opinions and I'm at the interesection where I have to decide whether I'm using them or others.
btw - kudos to Cloudflare for sponsoring this - seems like a great way to put yourself in front of developers.
If I'm guessing what the names of your Pingdom checks mean correctly, they seem to show CloudFlare making your response time 10ms slower. I'm assuming that cdnjs.cloudflare.com is the site with CF in front, and cdnjs.com is without, not sure if that's correct.
Looking at the headers both are being served by CloudFlare. And cdnjs.cloudflare.com is being redirected to cdnjs.com. So, I suspect that that's where the extra time comes from.
I think you're looking for an inverse relationship.
e.g. My car has 200hp and can do a quarter mile in 20 seconds. If I then increase my car to 400hp (a 100% increase), let's pretend I can now do a quarter mile in 10 seconds.
Thus, a 100% increase in performance drops cuts my quarter mile (or in this case processing) time in half.
