Questions[cdn](server)

I found this explanation how a CDN works. But there is one thing I don't really understand. Let's assume I setup multiple DNS servers at my location and they use the nameserver domains dns1.example.com, dns2.example.com and dns3.example.com. This DNS servers are able to deliver a server IP depending on the visitors location (ping, geo database, browser language or whatever). Now I update this nameserver settings for my domain www.example.org at the registry.

Now, the very first request on www.example.org with an expired TTL tries to resolve the domain. It asks:

1. the local .hosts/DNS, if TTL expired:
2. the internet providers DNS, if TTL expired:
3. the root DNS, if TTL expired:
4. my local dns1.example.com

But if I understand it correct, the new IP is then added to all these nameserver caches until the TTL expires again. So how is it possible to send other IPs to the visitor depending on his location?

In this answer theandym said the request is "forwarded", but I don't think this is how a CDN works, because "forwarding" means lengthen the transmission way resulting a longer loading time. Or does a CDN require zero TTL for the domain?

Update1
Through this question I found Google's document describing how they optimized CDN performance. It did not explain how the CDN works in general, but there were interesting explanations like the following:

Thereafter, whenever a client attempts to fetch content hosted on the CDN, the client is redirected to the node determined to have the least latency to its prefix. This redirection however is based on the prefix corresponding to the IP address of the DNS nameserver that resolves the URL of the content on the client’s behalf, which is typically co-located with the client.

This means Google checks at first the latency of all IP prefixes and defines a DNS resolution table (?) for all available prefixes. And if a visitor has the IP 198.51.100.231 the Google server IP is used, that is set for the prefix 198.51.100.0. But again: How does Google's DNS know which IP the visitor is using? Most visitors resolve Google's domain through their internet provider and by that the resolving is done through those external DNS servers or not?

As an additional example: If I start a DNS resolution for the domain facebook.com with different online tools (hosted in different countries) it is resolved to different IPs with different domains like:

• 31.13.92.36 Reverse: edge-star-mini-shv-01-frt3.facebook.com
• 31.13.76.68 Reverse: edge-star-mini-shv-01-sea1.facebook.com
• 31.13.69.228 Reverse: edge-star-mini-shv-01-iad3.facebook.com
• 157.240.2.35 Reverse: edge-star-mini-shv-01-ort2.facebook.com

After that I thought it could depend on the DNS server location used by the visitor, but I tried my own (Deutsche Telekom, Germany), Google's (8.8.8.8) and a major one from France (Orange) and they all returned for facebook.com the IP 31.13.92.36.

We just migrated to Amazon AWS. We currently have an EC2 instance that's working well. It's running Nginx in front and Apache in the back-end. That's running well also. All sites are launched properly and includes the Cache-Control header for files that are served from the EC2.

The problem is with ALL static files we placed in Amazon S3 that's being accessed through CloudFront CDN. We can access the files fine (and no issue with CORS), but apparently CloudFront doesn't serve files with Cache-Control header. We want to leverage on browser caching.

The way I see it, the EC2 instance doesn't play a role here as the static files are being served directly by S3+CloudFront, the request does not go to the Web Server in EC2.

I'm at a complete lost.

Question: 1) How do I set the Cache-Control in this case? 2) Is it possible to set the Cache-Control? From S3 or CloudFront?

Note: I've hit a few pages in Google where you can set the Header in S3 for individual objects. That's really not a productive way to do it specially since in my case we are talking of several objects.

Thanks!

I have been put in charge of setting up a CDN account for streaming video but am not actually running the site that will host the content. How can I test that a published RTMP URL is working? Do I need to create a test page with a Flash video player or is there a simple tool that can consume RTMP streams that can be used to test? The URL is in the following format:

rtmp://example.fcod.llnwd.net/a1111/e11/test/example/file.flv

I am planning on moving my static files to Google's App Engine. I was wondering if this is a good idea to do.

I have read that is it possible that Google will cache your files on multiple locations, which is a good thing in my opinion.

The setup should also be quite easy in eclipse with the GAE plugins.

But i still have my doubts on the performance of this. Is the setup of App Engine optimized for serving static content. Now I have Nginx server my static content, will App Engine perform the same way.

Are there any other ups or downs using this method?

I work for a Fortune 500 company that struggles with accurately measuring performance and availability for high availability applications (i.e., apps that are up 99.5% with 5 seconds page to page navigation). We factor in both scheduled and unscheduled downtime to determine this availability number. However, we recently added a CDN into the mix, which kind of complicates our metrics a bit. The CDN now handles about 75% of our traffic, while sending the remainder to our own servers.

We attempt to measure what we call a "true user experience" (i.e., our testing scripts emulate a typical user clicking through the application.) These monitoring scripts sit outside of our network, which means we're hitting the CDN about 75% of the time.

Management has decided that we take the worst case scenario to measure availability. So if our origin servers are having problems, but yet the CDN is serving content just fine, we still take a hit on availability. The same is true the other way around. My thought is that as long as the "user experience" is successful, we should not unnecessarily punish ourselves. After all, a CDN is there to improve performance and availability!

I'm just wondering if anyone has any knowledge of how other Fortune 500 companies calculate their availability numbers? I look at apple.com, for instance, of a storefront that uses a CDN that never seems to be down (unless there is about to be a major product announcement.) It would be great to have some hard, factual data because I don't believe that we need to unnecessarily hurt ourselves on these metrics. We are making business decisions based on these numbers.

I can say, however, given that these metrics are visible to management, issues get addressed and resolved pretty fast (read: we cut through the red-tape pretty quick.) Unfortunately, as a developer, I don't want management to think that the application is up or down because some external factor (i.e., CDN) is influencing the numbers.

Thoughts?

(I mistakenly posted this question on StackOverflow, sorry in advance for the cross-post)