On 12/03/2015 05:23 AM, Nikhil Utane wrote: > Ken, > > One more question, if i have to propagate configuration changes between the > nodes then is cpg (closed process group) the right way? > For e.g. > Active Node1 has config A=1, B=2 > Active Node2 has config A=3, B=4 > Standby Node needs to have configuration for all the nodes such that > whichever goes down, it comes up with those values. > Here configuration is not static but can be updated at run-time.
Being unfamiliar with the specifics of your case, I can't say what the best approach is, but it sounds like you will need to write a custom OCF resource agent to manage your service. A resource agent is similar to an init script: http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#ap-ocf The RA will start the service with the appropriate configuration. It can use per-resource options configured in pacemaker or external information to do that. How does your service get its configuration currently? > BTW, I'm little confused between OpenAIS and Corosync. For my purpose I > should be able to use either, right? Corosync started out as a subset of OpenAIS, optimized for use with Pacemaker. Corosync 2 is now the preferred membership layer for Pacemaker for most uses, though other layers are still supported. > Thanks. > > On Tue, Dec 1, 2015 at 9:04 PM, Ken Gaillot <kgail...@redhat.com> wrote: > >> On 12/01/2015 05:31 AM, Nikhil Utane wrote: >>> Hi, >>> >>> I am evaluating whether it is feasible to use Pacemaker + Corosync to add >>> support for clustering/redundancy into our product. >> >> Most definitely >> >>> Our objectives: >>> 1) Support N+1 redundancy. i,e. N Active and (up to) 1 Standby. >> >> You can do this with location constraints and scores. See: >> >> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#_deciding_which_nodes_a_resource_can_run_on >> >> Basically, you give the standby node a lower score than the other nodes. >> >>> 2) Each node has some different configuration parameters. >>> 3) Whenever any active node goes down, the standby node comes up with the >>> same configuration that the active had. >> >> How you solve this requirement depends on the specifics of your >> situation. Ideally, you can use OCF resource agents that take the >> configuration location as a parameter. You may have to write your own, >> if none is available for your services. >> >>> 4) There is no one single process/service for which we need redundancy, >>> rather it is the entire system (multiple processes running together). >> >> This is trivially implemented using either groups or ordering and >> colocation constraints. >> >> Order constraint = start service A before starting service B (and stop >> in reverse order) >> >> Colocation constraint = keep services A and B on the same node >> >> Group = shortcut to specify several services that need to start/stop in >> order and be kept together >> >> >> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#idm231363875392 >> >> >> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#group-resources >> >> >>> 5) I would also want to be notified when any active<->standby state >>> transition happens as I would want to take some steps at the application >>> level. >> >> There are multiple approaches. >> >> If you don't mind compiling your own packages, the latest master branch >> (which will be part of the upcoming 1.1.14 release) has built-in >> notification capability. See: >> http://blog.clusterlabs.org/blog/2015/reliable-notifications/ >> >> Otherwise, you can use SNMP or e-mail if your packages were compiled >> with those options, or you can use the ocf:pacemaker:ClusterMon resource >> agent: >> >> http://clusterlabs.org/doc/en-US/Pacemaker/1.1-pcs/html-single/Pacemaker_Explained/index.html#idm231308442928 >> >>> I went through the documents/blogs but all had example for 1 active and 1 >>> standby use-case and that too for some standard service like httpd. >> >> Pacemaker is incredibly versatile, and the use cases are far too varied >> to cover more than a small subset. Those simple examples show the basic >> building blocks, and can usually point you to the specific features you >> need to investigate further. >> >>> One additional question, If I am having multiple actives, then Virtual IP >>> configuration cannot be used? Is it possible such that N actives have >>> different IP addresses but whenever standby becomes active it uses the IP >>> address of the failed node? >> >> Yes, there are a few approaches here, too. >> >> The simplest is to assign a virtual IP to each active, and include it in >> your group of resources. The whole group will fail over to the standby >> node if the original goes down. >> >> If you want a single virtual IP that is used by all your actives, one >> alternative is to clone the ocf:heartbeat:IPaddr2 resource. When cloned, >> that resource agent will use iptables' CLUSTERIP functionality, which >> relies on multicast Ethernet addresses (not to be confused with >> multicast IP). Since multicast Ethernet has limitations, this is not >> often used in production. >> >> A more complicated method is to use a virtual IP in combination with a >> load-balancer such as haproxy. Pacemaker can manage haproxy and the real >> services, and haproxy manages distributing requests to the real services. >> >>> Thanking in advance. >>> Nikhil >> >> A last word of advice: Fencing (aka STONITH) is important for proper >> recovery from difficult failure conditions. Without it, it is possible >> to have data loss or corruption in a split-brain situation. _______________________________________________ Users mailing list: Users@clusterlabs.org http://clusterlabs.org/mailman/listinfo/users Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org