On Monday 05 November 2007 08:42, Michael MacIsaac wrote:
>Jae Hwa,
>
>> How about rpm update works(except kernel updates) for these
>> systems using shared root fs? Are there any ways to apply
>> the updates to many cloned system?
>
>Good question. The short answer is that I defer to either Steve Womer, if
>he cares to comment, or to the current thread "Applying updates to
>multiple servers".
The core problem here is how to install (or update) and RPM on a cloned Linux
guest when it shares filesystems with other guests. Shared filesystems have
to be read-only, so attempting to install an RPM that contains files that are
to go into a shared filesystem on the cloned system will fail. What you have
to do is shut down all guests that share the filesystem so that you can then
bring up one guest that mounts the filesystem read-write. You then install
the RPMs on that guest, figure out which files were changed in all the
non-shared filesystems, and write them into the filesystems of all the other
guests. Finally, you shut down the guest that mounted the shared filesystem
read-write, and start all the guests so that they are sharing the altered
filesystem read-only again, and have the updates on their non-shared
filesystems.
<shameless-product-plug>
I'm quite familier with this problem because I've implemented a variation of
the above in Mainstar's Provisioning Expert for Linux on z/VM to automate
updates to many guests. We found a way to avoid taking all the guests down
for a long time, though, so you can apply the same update to individual
guests or groups of guests and it takes each one down only while altering its
non-shared filesystems, which is usually just a few minutes.
</shameless-product-plug>
It's not a trivial thing to do, and automating it with a tool is pretty much
the only way to get it done right. I've heard that Nationwide built scripts
to push out updates, but I don't know if they do that for their "shared root"
guests or not.
- MacK.
-----
Edmund R. MacKenty
Software Architect
Rocket Software, Inc.
Newton, MA USA
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