Great help! Please allow me to trouble you with one last question.
If I get this, when I use fencing and the corosync fails then linux-2 will
attempt to crash linux-1 and take over. At this point though linux-1 won't try
to do anything right? Since it knows it is the primary, I mean.
Then you say:"Any
resource previously running on linux-1 will be started on linux-2."
Now at this point: By resource you mean only pacemaker and its related modules,
right? Because I want Tomcat to be up and running and receiving requests in
Linux-2 as well, which will be forwarded by load balancer of linux-1. Is this
correct?
Also in your setup of 2 NICs or 2 switches I assume that the idea is that the
probability of split-brain due to network failure is very low right? Because I
have read that it is not possible to avoid split-brain without adding a third
node. But I may be misunderstanding this
________________________________
From: David Coulson <[email protected]>
To: Hermes Flying <[email protected]>
Cc: General Linux-HA mailing list <[email protected]>; Digimer
<[email protected]>
Sent: Saturday, December 1, 2012 3:26 PM
Subject: Re: [Linux-HA] Some help on understanding how HA issues are addressed
by pacemaker
On 12/1/12 8:21 AM, Hermes Flying wrote:
Thanks for your reply.
>First of all I didn't get if the VIP will migrate if Tomcat or
load balancer also fails. It will right?
>
If you configure Pacemaker correctly, yes.
Also if I understand this correctly, I can end up with VIP on both nodes if
corosync fails due to network failure. And you suggest redundant communication
paths to avoid this.
>But if I understand the problem, if the VIP runs in my linux-1
and pacemaker is somehow via corosync ready to take over on
failure from linux-2, if there is a network failure (despite
redundant communication paths, unless you guys recommend some
specific topology to the people using Pacemaker that you are
100% full proof) how can you detect if the other node is
actually crashed or just corosync fails? In this case won't the
linux-2 also "wakeup" to take VIP?
>
That is what fencing is for. If linux-1 goes offline from the perspective of
linux-2, linux-2 will attempt to crash/power-cycle/power-off linux-1 to ensure
it is really dead. Any resource previously running on linux-1 will be started
on linux-2.
Usually with a two node config I take two NICs on each box and
connect them directly to the other one - Also would work if you had
two separate switches you could run each path through. Then I use
Linux NIC bonding to provide redundancy and run corosync over the
bond interface.
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