[Linux-ha-dev] Ordering of OCF Start, Stop and Monitor actions

[Andrew Beekhof]

On 3/20/07, Doug Knight <dknight at wsi.com> wrote:
>
>  Hi Alan,
>  I've had some time to try to implement the OCF script for the PostgreSQL
> WAL file forwarding configuration, and I still am having some issues. The
> main issue is how do I set up an OCF script that allows the process to run
> on both servers, one process in a "starting" mode ingesting transferred WAL
> files, the other in an "accessible" mode allowing database access and
> forwarding WAL files to the standby (right now the different states are
> determined within the OCF script by looking for the existence of a
> recovery.conf file, which indicates the "starting", standby side)? What I'm
> trying to figure out is how to tell HA that it needs to start the standby
> process and monitor it.
>
>  I've started looking at the multi-state configurations, but the
> documentation isn't completely clear. Can you expand on it? I'd like
> something similar to the answers you gave for the monitor, stop, and start
> functions (when do they/can they get invoked, on which node, etc). One
> specific area of the multi-state config I have a question about is how to
> tell HA which server has the master role when first starting up the
> resource. Any additional info would be great.

have a look at the drbd and Stateful agents:
   http://hg.beekhof.net/lha/crm-dev/file/be220f2e9b40/resources/OCF/Stateful.in

but first read:
   http://linux-ha.org/v2/Concepts/MultiState

in particular, section 6.1

>
>  Thanks,
>  Doug
>
>
>
>
>  On Wed, 2007-03-14 at 19:59 -0600, Alan Robertson wrote:
>  Doug Knight wrote:
> > Yes, Thanks Alan. Let me digest it, and walk through my OCF script. I'll
> > see if I have any other questions after that.
> >
> > Thanks for getting back to me.
> >
> > Doug
> >
> > On Wed, 2007-03-14 at 11:41 -0600, Alan Robertson wrote:
> >> Doug Knight wrote:
> >> > Hi All,
> >> > I currently am running a two node cluster (host1 and host2) with
> version
> >> > 2.0.8. I have a resource defined with a place constraint of "#uname eq
> >> > host1", so that it will start on host1 (using an OCF RA script,
> >> > including all of the required methods). The resource itself has
> >> > target_role set to "stopped".
> >> >
> >> > Question 1: Is the monitor method called regularly on both nodes to
> make
> >> > sure the resource is not running?
> >>
> >> No. It is called on every node when we first start up (we call it a
> >> probe operation). If you ask us to, we will run it periodically to
> >> ensure that a running copy continues to run.
> >>
> >> You can also manually request to run this initial probe again to catch
> >> errors made by system administrators (but I don't know of anyone who
> >> does that).
> >>
> >>
> >> > Next, I change the target_role to "started" (i.e. I use the GUI and
> >> > click the start button).
> >> [Better yet, use the "outline" start button]
> >>
> >> > Question 2: What is the order of OCF methods called to bring up the
> >> > resource? Is Monitor called before Start on host1? Does Stop and/or
> >> > Monitor ever get called on host2?
> >>
> >> Monitor gets called when we first start up on every node.
> >> It also get called repeatedly on any node that we think is running it --
> >> if you ask us to monitor the resource.
> >>
> >> > Resource is up and running on host1, and I decide to move the resource
> >> > to host2. I click the constraint and change it to "#uname eq host2".
> The
> >> > resource stops on host1 and starts on host2.
> >> >
> >> > Question 3: Same idea, what are the sequence of method calls to migrate
> >> > the resource from host1 to host2?
> >>
> >> In the past...
> >> monitor every resource on every node once to see what's already
> >> running
> >> start on "some node"
> >> monitor periodically on "some node" (if requested)
> >>
> >> Request to move resource arrives...
> >> stop monitoring on "some node" (if it had been requested)
> >> stop resource on "some node"
> >> start resource on "some other" node
> >> monitor periodically on "some other node" (if requested)
> >>
> >> > I'm trying to thoroughly understand the sequence of events that occurs
> >> > for each phase in support of the Postgres WAL file forwarding
> >> > configuration I posted last week ("[Linux-HA] Two node cluster with
> >> > Postgres in WAL file fwding mode", started March 1).
>
>
> Let me offer this caveat:
>
> Monitor might be called at any time.
>
> Stop should work at any time,
>  and succeed harmlessly if it's already stopped.
>
> Start should work at any time,
>  and succeed harmlessly if it's already started.
>
> http://www.linux-ha.org/OCFResourceAgent gives more
> details.
>
>
>
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