[Linux-HA] MMM conflict with Pacemaker
mark at grennan.com
Fri Feb 17 09:29:29 MST 2012
Did I say all this is confusing? Here is a really a great talk on HA. There is a good history of Linux HA and Pacemaker starting at about 9:00 minutes in. Some of parts of systems have been broken into project of their own while others have been combined. Cluster resource are at the heart of what you want done but this is also some of the smoke and mirrors that of some of these packages. Some just call your init scripts. (/etc/init.d) some call their on init scripts. (Heartbeat) and still others expect you to write your own.
> But pacemaker isn't even running on the machines the mmm float is on!
Remember MMM and MHA for that matter, use SSH, with certs, to reach out and run stuff on remote systems. Where pacemaker or MMM is running and what can be effected is a bit tricky.
> ...I can't understand why you're using a public IP for mcast, or why it's even there at all....
There are many refinements I could make to my setup document. I took some short cuts to help people just get it working. But, not so sort they would have to rebuild the system to make it better. Networking is one of them. I like to use multiple network interfaces to isolate the database traffic from all the "systems" traffic. Multi nics is also good because pacemaker can check through a different path.
> I'm still mystified by whether I should use ucast, mcast or bcast...
If I am using a crossover cable to connect two hosts together, I just broadcast the heartbeat out of the appropriate interface. (bcast eth3) If there are more then two hosts in the Pacemaker cluster on the same private network I use mcast.
> ...can't understand why you're using a public IP for mcast...
I'm using mcast because it's the best way to talk to multiple nodes and I expect some people will try that. 220.127.116.11 is not a public IP. (http://tldp.org/HOWTO/Multicast-HOWTO-2.html) The range 18.104.22.168 - 22.214.171.124 is reserved for Multi-Cast and the range 126.96.36.199 to 188.8.131.52 is reserved for this administrative scoping.
> My mmm config was originally installed by Percona, and I've done several others since.
MMM was the way to go until just recently. If it's working for you keep using it. But it may be already at it's end of life. Here is another resource (http://technocation.org/content/oursql-episode-67%3A-ha-and-replication) on what's been happening.
> One critical aspect of an HA system is that it should be really easy to deal with when things go wrong;
This may be the biggest problem with HA/MySQL systems. If you can't fix it when it breaks what good is it. And, complicated is the enemy or reliability.
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