Cloud versus cloud: A guided tour of Amazon, Google, AppNexus, and GoGrid

AppNexus

If you like the idea of the cloud but aren't sure if you want to leave behind the old trustworthy world of Unix, cron jobs, and other tools, then AppNexus is a service that aims to be a bit more transparent. The company has taken a big, industrial-sized server farm with the best load-sharing tools and storage boxes and found a way to let you buy it in small portions. AppNexus provides a number of command-line abstractions that let you turn servers on and off, but they also let you drill down into the file system.

The main functions of the AppNexus cloud are similar to Amazon's EC2. You log in through a command line and boot up images of Linux distributions. AppNexus says it can rebuild images from other sources like Amazon's EC2 by replacing the kernel with a version that's more aware that it is running in a virtual environment. Then it just takes a few key clicks on a command line to set up a load balancer.

One open question in the world of cloud computing is where the abstraction occurs; that is, where do the walls between the machines become blurred and it all starts to look a bit cloudy? Amazon's SimpleDB hides the storage behind a software wall and gives you access to it through some Web service call. AppNexus is working at a lower level by building in a cluster of Isilon IQ X-Series storage clusters into its cloud.

This gives you the option of simply mounting the storage and sharing the data across your cluster of servers -- if you consider that simple. Instead of working with abstract keys, you use real file names as the keys. The cluster handles the rest of the work.

A better solution is to use what AppNexus calls its CDN, or Content Delivery Network. The storage cluster has its own set of HTTP servers built in, and you can automatically begin serving static data from your files. Just write the files to the /cdn directory and they become available. AppNexus will distribute this storage cloud to multiple datacenters, making it simpler to serve up the static data from the closest location. (See the QuickTime video.)