[K12OSN] Not recreating the wheel
Christopher K. Johnson
ckjohnson at gwi.net
Fri May 14 12:05:56 UTC 2004
Jim Wildman wrote:
>On Thu, 13 May 2004, Lewis Holcroft wrote:
>Wow. That was quite a diagram!
>I would not do the nfs over the isdn lines. rsync will work fine to
>keep the boxes in sync for basic file stuff, either pushing from the
>master for pulling from the client end. For the people who move around,
>just set an rsync job for them that runs more often than they can get
>between the 2 closest buildings. It doesn't have to be fast, just
>faster than them.
>While folks like to talk about instantenous access to everything, in
>reality the cost to go from "you will never wait more than 15 minutes" to
>"instaneous" can be rather prohibitive.
The tricky thing about using rsync, is that you need to make it work in
the correct direction. When not logged in at an alternate location it
needs to sync all other sites to the person's primary site. When logged
in at an alternate location it needs to sync all other sites to that
alternate copy of their home directory. And if you do it with cron jobs
there is a problem with changes after logging off at an alternate site
being sync'd the wrong way. So you need to manage some state
indicator (a file touched at logon and cleared by cron job only if the
person is no longer logged on) that will enable the cron job to do the
right thing that one last time after logoff.
I'm not saying it can't be done. In fact provided a time lag for travel
between sites I'm sure it could be done. You just have to tackle these
issues to make it work right.
By the way, what will remain problematic in the rsync scenario is if
someone actually does log on remotely to a system. The worst case is
when they simultaneously log on to more than one system. What should
the rsync cron jobs do then and how will they detect that condition to
accomodate it? Perhaps you need to tell people "don't log on to more
than one server at a time".
"Spend less! Do more! Go Open Source..." -- Dirigo.net
Chris Johnson, RHCE #807000448202021
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