HA clusters in 20 minutes

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Sander van Vugt sounds like that he's done this talk before. Normally he tries to get 3 hours for this talk, but he's only got 20 minutes. He wrote a book ('A Practical Guide to Xen HA', he's happy to email a pdf of the book. He's written a bunch of other books as well.

He mentioned corosync is used for the cluster communication layer. They communicate using multicast address. He mentioned a crm gui and crm shell interface. The bulk of his presentation was actually a demo.

He's using a syse, and hence the yast2 setup. He picked a random 239.0.0.0/24 address, which is a private address space for multicast.

I wasn't really out to fit this idea of clustering into my brain of where you'd use it for, and what. So I was struggling to follow this talk. I wasn't going to ask for any background, as I'm sure other people were right upto speed on this. It sounds like the cluster can be used for a bunch of different things. He mentioned different modes the nodes in te cluster can operate. He talked about a cluster aware file system that could be used, or a master mode where nodes could be setup as a master.

Another example he used was a cluster where both machines could mount an ext3 filesystem, but they had a problem where both hosts tried to open the filesystem at the same time, and once they were both writing the filesystem it all got broken.

He mentinoed that in a cluster you need STONITH (Shoot the other node in the head). So that when the cluster detects a node has stopped functioning, the cluster can force the shutdown of a host, by either a rack PDU force powering down, or triggering a kernel panic.

You need resource monitoring, so you know if your resources are working. You need to remove the resources from your runlevels, so the cluster can start the resource, instead of the resource starting on bootup.

Resource stickineess is about how bad the resource wants to stay on the node it currently running on. So he suggests setting a positive value to ask the cluster to leave the resource on the node it's running.

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This page contains a single entry by Geoff Crompton published on January 25, 2011 12:44 PM.

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