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VmWare and virtual servers

Following Joel's latest posting, I saw a recent article suggesting that Microsoft's acquisition of Connectix might be because they have very similar ideas in mind - virtualise servers.

http://www.connectix.com/about/acquisition_win.html

Robert Cowham
Tuesday, June 03, 2003

IBM has been offering this capability for years in their high-end AS/400 mainframe products.  Currently on an AS/400, you can load and run multiple Linux servers at the same time, assigning each one a different ip and hostname, so that you can have a virtual cluster.  In environments where 99.999% uptime is a necessity (bank transactions, stock market, air traffic control) this kind of virtualization is commonplace.

One of the big steps forward with Java was to bring this kind of virtualization to the mid and low end.  JVMs internally support a high degree of virtualization (with heirarchical classloaders and garbage collection) and the JVM itself is a virtual machine, making it easier to hot-deploy and upgrade servers.  Buggy Java software also will generally only generate an exception, or at the worst take down the JVM.  Compare this with the core dumps and segfaults that come on Unix and Windows systems using native code, and debugging and restoring code and servers is much easier because of the protection offered by the JVM.

Colin Evans
Tuesday, June 03, 2003

How do you take out a java class and replace it with another while a JVM is running?

Li-fan Chen
Tuesday, June 03, 2003

You need to write a specific class loader. Many java application server implementation have this feature. Ex: Tomcat, jBoss, ...

Robert Chevallier
Tuesday, June 03, 2003

If you want the implementation details, look at these projects. They are open-source

Robert Chevallier
Tuesday, June 03, 2003

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