Re: [vserver] HA vserver in an active/active configuration

On Tue, 5 Feb 2008 14:00:23 +0100 Jon Bendtsen wrote:
> On 03/02/2008, at 11.07, Christian Balzer wrote:
>
> >
> > Hello,
> >
> > 2 hosts, shared storage (SAN, DRBD, iSCSI, it doesn't really matter)
> > and Linux HA aka heartbeat as a CRM. The obvious goal is to have the
> > vservers on host A to fail over to B if need be.
> > The equally obvious problem is that util-vserver is expecting the
> > configs
> > in /etc/vservers and the vserver command has no command line option to
> > specify the config directory.
>
> If you use a different mark in /etc/vservers/*/apps/init/mark
> Like A or B, and then start the respective vserver guests
> for the respective real servers. Should the other server fail,
> just start the vservers with that servers mark.
>
> That way you should be able to keep all /etc/vservers/* copied
> on all servers without problems.
>
That is thought, but it requires to keep /etc/vservers in sync
between the nodes. Which do share the storage, but don't have
active/active mounted cluster filesystems (none of them have
impressed me in the past in terms of feature completeness and/or
speed and adding them into the mix with vserver sounds too much like
a giant headache to me).

> You might also be able to keep the "home" dirs in /var/lib/vservers/*
> copied.
>
And mount them individually below there? Which reminds me to
thank Martin Fick for the Fail-over link on the vserver wiki.
It was a good read, but I'm not planning to have individual
partitions for each vserver, too much overhead and too rigid
when it comes to disk quotas.

So what I'm planning to do is ideally to just have one partition
per cluster node, which gets mounted on the other one in case of
node failure. With a structure something like:

/data-a/etc/vservers/
/data-a/vservers/vserver-001/
[...]

and /etc/vservers and /var/lib/vservers pointing to the respective
directories on the node that is the default host for these. So
with nothing failed over, vserver-utils will work just fine and
out of the box. In a fail-over case (lets say node B to A), the OCF script
will just have to do a "vserver /data-b/etc/vservers vserver-n start" for
each vserver, the list of which it of course could determine by a "mark".

In case I go with a uniform/shared config in /etc/vservers, I would still
have to mount the actual vserver partition like:
/var/lib/vserver/data-a/ [vserver-001...]
/var/lib/vserver/data-b/ [vserver-050...]

to avoid barrier issues, right?

Well, the production hardware should arrive in 2 weeks and then the fun
shall begin for real. ^_^

Regards,

Christian

-- 
Christian Balzer        Network/Systems Engineer                NOC
chibi@gol.com   	Global OnLine Japan/Fusion Network Services
http://www.gol.com/