Re: organizing virtual machines

["Eric S. Johansson" <esj@harvee.org>]

Tom Hibbert wrote:
> There is no requirement for seperating partitions on installation. This
> is considered a best practice because in the event of a partition
> faliure it increases the chance of recovering at least part of the
> system. In the purists world, / is mounted read-only and the only parts
> of the disk that can be written to without mounting readwrite are /var
> and /home. 

(knock wood) I've never had a partition failure.  They have always been 
more on the lines of "*%#@%@ I lost another drive".

> Absolutely true. However, it is possible to have a shared root/usr using
> NFS, with independent /var, /home and /etc. This is a common
> configuration for clusters and big iron.

intriguing.  Makes sense and one could also do this with the dom0 
serving all the other virtual machines.  would have some problems with 
/etc however

> Dogs breakfast? 

yea.  a.k.a. "recycling" and in the wintertime "Poopsicles".

> Only in the event of badly constructed packages or an
> inexperienced aministrator installing from source should there ever be
> any configuration data stored outside of /etc. This is the sole reason
> /etc exists. I don't consider it a dogs breakfast at all, even under
> Gentoo.

I must politely disagree.  In the example you gave above where root 
end-user are shared, what happens when you change a program that also 
has a related change in /etc?  At best, nothing bad happens.  At worst, 
you start getting random failures that drive you mad until you finally 
get all of the images changed.  Sometimes it's a simple replication. 
More often than not it's customized changes on all machines.

Even updating a single machine it can be a "this sucks" moment.  I 
cannot tell you the number of times I have updated gentoo and found that 
I had to slog through 50 configuration file changes.

so, the reason I consider virtually all system configuration 
directories, registries etc. a dogs breakfast is that they don't handle 
change well and the changes are not replicated properly.

my fantasy world for proper system configuration management would record 
baseline and changes so that when baseline changes one can re-create the 
working configuration set (i.e. /etc).  For a virtual machine 
environment like xen, one could have virtual machine associated changes 
with a common baseline so that when you update your executables and 
configuration directory, all the changes replicate properly or can be 
flagged for human attention.

I'm planning a working on this when I have some spare neurons.

---eric

-- 
http://www.salon.com/books/review/2004/12/18/heloise/index.html

The basis of Abelard's philosophy, which he taught to Heloise, was
that logic had to be applied to religion in order to arrive at the
truth.


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