On 20/04/15 08:29 AM, Lentes, Bernd wrote: > Hi, > > we'd like to create a two-node cluster for our services (web, database, > virtual machines). We will have two servers and a shared fiberchannel SAN. > What would you do e.g. with the content of the webpages we offer ? Put them > on the SAN so we don't need to synchronize them between the two nodes ? Also > the database and the vm's on the SAN ? Which fs would you recommend for the > SAN volumes ? OCFS2 ? Can I mount the same volume on each node contemporarily > ? Or do I have to use the ocfs2 as a resource managed by pacemaker, so that > the volume is only mounted if it is necessary ? > > Thanks for any hint. > > > Bernd
You're trying to make your website HA, specifically? Assuming so, you have two main options; 1. Application level HA 2. Server (VM) level HA The benefit of #1 is that failover and recovery is usually faster, but the downside is complexity. The benefits of #2 are that the HA is obfuscated away from the application, migrating the service between nodes is seamless/no interruption and the HA setup is portable to other apps without modification. If you never plan to create another HA anything, then part of the benefit of #2 goes away. Personally, I am a big fan of keeping things as simple as possible. By making the server HA, you need to change nothing about your application stack. If the host fails, the cluster simply reboots the server on the backup, done. Being a VM, reboot times are (in my experience, across many OSes) 30~90 seconds to get back to the OS login screen (plus stack startup, but that is negligible for most web server stacks). Then you can create new servers on the same config (even OSes like MS Windows) and they're magically HA as well, nothing more to do. If you prefer #1 though, that is OK as well. The question then becomes more about your particular needs, as the setup will be customized per environment. Generally speaking, you want to avoid active/active if you can avoid it. The reason being that clustered file systems, by the very nature of their locking needing to be coordinated and clustered, comes at a performance cost. People often think "well, I have two nodes, why not double my performance?". It is sensible on the surface, until you realize the complexity. If you can get away with it, I'd use active/passive. In this case, only one node will have your LUN at a time, hosting a traditional FS ext4/xfs, and the data for your HA stuff on the LUN. The node that is the current host would: Connect the LUN -> mount the FS -> start the services -> take a floating/virtual IP. Migrate the service is: Old Active; Take down the IP, stop the services -> dismount the FS -> disconnect the LUN New Active; Connect the LUN -> mount the FS -> start the services -> take a floating/virtual IP. (This is why having your service in an HA VM is better for migration; No 'stop' needed, live-migration causes no interruption). Recovery from a crashed/failed active; Fence the lost node -> Connect the LUN -> mount the FS -> start the services -> take a floating/virtual IP. To get into anything more specific, you will need to be more specific about your priorities and the details of your setup. -- Digimer Papers and Projects: https://alteeve.ca/w/ What if the cure for cancer is trapped in the mind of a person without access to education? _______________________________________________ Pacemaker mailing list: Pacemaker@oss.clusterlabs.org http://oss.clusterlabs.org/mailman/listinfo/pacemaker Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org