I was pleased to find that since the Mediawiki source files Id copied onto my original server had been stored not on the server component itself but on a virtual NAS (network-attached storage) device within my application, my Mediawiki files were waiting for me when I fired up my application. I also had the option of swapping out my single Web server with a four- or eight-pack of virtual servers, complete with an integrated virtual load balancer. In this way, I could take advantage of the four separate physical machines in my test grid while spending as little time as possible fiddling with the particulars of each component. This makes load-sharing fairly transparent and allows for practically built-in failover in case of hardware crashes.As with other virtualization products, AppLogics individual VMs run only on one physical machine at a time. If the machine thats hosting a VM goes down, that VM goes down as well. When that happens, AppLogic restarts the interrupted VM on another machine in the gridmuch like VMware ESX or Virtual Iron do. Unlike VMware ESX or Virtual Iron, however, AppLogic provides for the shared storage necessary to enable VM migrations by aggregating the local storage on each of a grids physical servers into a mirrored RAID. 3PAR sells a product that adds this functionality to VMware ESX server, but, out of the box, ESX and most other virtualization products either ignore local storage or make it available only to the host on which its installed. Its possible to connect an iSCSI SAN (storage area network) to an AppLogic grid by linking it to the virtual network interfaces of individual VMs within an application, but, according to 3Tera officials, few AppLogic customers use this configuration. Software Support AppLogic relies on Xen for its virtualization, so as long as the servers that comprise an AppLogic grid include processors with hardware-assisted virtualization, its technically possible to run any x86 or x86-64 operating system. For now, AppLogic supports only Linux. According to 3Tera officials, the next operating system in line for official support is Solaris, followed by FreeBSD and then Windows. While Xen can run unmodified operating systems, AppLogic guest machines do require some particular software to partake in the products grid environment. In my tests, I encountered a snag related to these services. After I applied all available updates to my CentOS 5-based VM and restarted my Mediawiki application, the application failed to start properly. As it turns out, the update broke the services required to participate in the grid. Based on my tests with AppLogic, it appears that tending to your application component templates will be the most time-consuming part of deploying workloads on AppLogic. Id love to see 3Tera forge partnerships with companies focused on delivering software appliances--such as rPath, Red Hat, VMware or (eventually, at least) Microsoft--to make it easier to deploy AppLogic grids on the software appliances that these companies provide or aggregate. Check out eWEEK.coms for the latest news, views and analysis on servers, switches and networking protocols for the enterprise and small businesses.
In fact, at one point during my tests, one of the four physical machines in my grid went down, and, while I could see from the AppLogic Web interface that I was down a machine, the outage did not affect my testing.