[Gllug] Back-out plans on Debian/Redhat?

[Alain Williams]

On Sat, Mar 07, 2009 at 11:15:25AM +0000, Khusro Jaleel wrote:
> Hi, I was reading
> 
> "The Practice of System and Network Administration"
> http://www.amazon.co.uk/Practice-System-Network-Administration/dp/0201702711
> 
> and the chapter on Change Management states that you must have a
> back-out plan in case of problems when you are making major updates to
> a system.

Depends on how important the system is, ie does it matter if some
functionality isn't there for a few hours/days while you fix it.

Updates within a major release tend to not cause problems, the only
one that has hit me recently (on CentOS) was a nagios update in Dec,
where the location of some files was changed ... easy to fix once
I realised that nagios was stopped.

If I do something that I am unsure of, either because it is very new
or I have not used it before I will often install first on a test machine.
My test machines these days tend to be virtual machines (KVM).

> What I'm not sure about is for example, if I have a critical
> Debian-based webserver which has a lot of updates due (Apache, Mysql,
> Kernel, Libc, etc) how do I implement a back-out plan for
> dist-upgrades in case there are problems?

Package managers tend to work well for upgrades of stuff, downgrading
to a previous release is dodgy -- if the upgrade script has changed
things, you prob aren't aware of it and since there isn't a 'downgrade'
script you are stuck.

Hence my previous comment: if it is really important do in test.

-- 
Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/
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Past chairman of UKUUG: http://www.ukuug.org/
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