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Thursday, June 05, 2003 |
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Our local Microsoft guru, Ken Durigan, threw a small wrench into my vision of using virtual servers to consolidate application servers. According to Ken both VMWare and VS (sign in with guest id "vspreview") use a web server to expose a management console. That means the server's host OS is still vulnerable to attack. That, in turn, means the server will have to be brought down to apply security patches. For most web applications this is not a big issue. We commonly set up a virtual IP address for web applications that resolves to an intelligent switch (e.g. Foundry's ServerIron) which then directs the request to one or more physical IP addresses. Taking a server offline in this model is fairly simple because the switch recognizes when the server is offline and stops sending requests to it. If the virtualized instances are hosting applications that are not load-balanced, however, you have a more difficult problem - one in which some down-time cannot be easily avoided. Worse, multiple applications are going to be affected. I think virtualization of production servers is still a viable strategy for providing application isolation. It still allows me to avoid the "required upgrade" syndrome described yesterday. Upgrades to the host OS, however, are going to cost a little bit of flexibility unless we provide architectural solutions (e.g. load balancing). |
