How Managed Virtualization (including HA) conflicts with System Management
Managed Virtualization Versus System Management
In an earlier post, I talked about a couple of kinds of virtualization, comparing two of them and highlighting their strengths. This posting discusses how virtualization can confuse and confound conventional systems management – both automated and manual, and gives some thoughts on how to deal with it.
We all know that virtualization is a GoodThing(TM). Therefore, it can’t really have any disadvantages, can it? <tongue-in-cheek-off> Unfortunately, it does have disadvantages. The great strength of virtualization is its ability to break the ties between a service or operating system and the server which implements its service. Many software systems and a good number of human administrators find this confusing. If I want to reboot a physical server, what services or operating systems will be disrupted by the reboot?
Conversely, if I want to do something to the machine that’s running a particular service, which machine do I have to log into? If you’re running both service virtualization (conventional HA like Linux-HA) on top of server virtualization (ala Xen or VMware), then you have a doubly difficult task – first you have to figure out which virtual machine is running a service, then you have to figure out which physical machine is running that particular virtual machine.
This can be really annoying and can easily result in system administrators making mistakes either in the middle of the night, or when under pressure (which all sysadmins know is pretty much all the time).
Remember – Complexity is the Enemy of Reliability. This is just another example of my favorite phrase at work.
And, if you want to have server monitoring software which tries to figure out whether a service is stopped and have it restart it, then it can also get confused by the fact that all these stupid servers and services are always moving around. They just won’t stay put! Back in the olden days, you logged into a server and you edited the inittab, and you always knew what hardware it was running on and what server it was. Now, with virtualization, and especially with virtualization management software, you never know what’s where.
To learn more and to read the entire article please refer to the rest of the article at its source: Managing Computers with Automation: How Managed Virtualization (including HA) conflicts with System Management