Hi,
I'm new to Linux HA and I am already a bit puzzled by a few things. I have two
AMD64 Opteron machines (same hardware config) running SuSE 10.2 and HA. I
managed to configure HA using the GUI and all the wizards I managed to bump
into. It seems to work. The thing is I look at it like at a blob of something
unknown to me and I keep circling it and poking it trying to understand how to
interact with it...
First, I am a little confused by some terminology/behavior. It seems I can use
the GUI on each of my two nodes to set them to standby or active mode (each of
the 4 combinations is accepted). I also read that a node can be master, DC
(decision coordinator), active, passive. Well, all of a sudden, a node can be
many things I think i understand individually but all together confuse me. In
my mind one node in the (2-node) cluster (in my case) is the boss (active) and
the other one is in standby waiting to become active after a failover. This
simple model I have in my mind is definitely challenged by the plethora or
adjectives I listed above, plus by combinations of all active (everyone is
the/a boss) / all standby (anarchy) which seems to be acceptable.
In addition to this, I don't really understand how to interact with HA once it
is up and running. I am writing some software that needs to be able to query
the cluster and find out information about the nodes. It seems crm_mon can help
with this. It gives the list of nodes and which one is DC ( is this what I
think of as THE active node / the boss?). I get the host names and I can figure
their IP addresses separately so that should be fine (wouldn't mind if I could
find this info from HA directly, but doing this separately is not a big deal).
Another source of confusion for me is the fact taht using the GUI I need to
connect to a cluster and provide a password while invoking crm_mon from the
command line goes straight to a"default" cluster (the only one actually) and
fetches information without any need for a password. Now I understand that the
GUI does more than return some info, it can actually manipulate the cluster but
would this be the reason why I don't need a password for crm_mon? It feels like
anybody should be able to look and one's bank account but it takes a password
to make a payment or transfer funds. The first half seems just wrong.
I would also like to be able to force a failover and I am guessing there should
be some command that would do this, is this true? How do I force a failover? Is
there a way to figure that the failover is complete?
Sorry about the avalanche of blurb and questions, but I really hit my head
against all of these and I tried to answer them by myself before asking for
help here and they kind of piled up on me.
Thanks for any kind answer you may have for me! Pointers to literature would be
greatly appreciated (I have read the linux-ha.org webpages as well as some
Novell documentation and yet I had to send this email out).
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