Ignore this, I re-sent to ClusterLabs. On 20/04/15 09:36 AM, Digimer wrote: > 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