[OpenAFS] Client update and failover for afsdb hosts

[Benjamin Kaduk]

On Thu, Aug 22, 2019 at 02:53:13PM -0400, Steve Simmons wrote:
> To make a long story short, we're going to be moving the network on which
> our afsdb servers reside from one data center to another. Trust me, you
> don't want to know the details. This will required a period of time wherein
> all the current afsdb hosts are down. The fileservers will not be affected.
> 
> To minimize the pain during the transition, we're temporarily adding a
> fourth non-voting server and updating CellServDB files appropriately. Some
> questions have come up about how the clients will react to this change and
> the best strategy to pursue for them. Complicating this are clients running
> various versions of openafs, most of which are recent 1.6/1.8, but there
> are a few 1.4.14/15 clients out there. All the clients referred to here are
> running various flavors of Linux. Yeah, I could read the code  for all
> those versions, but in case someone happens to know:
> 
> Does a client read the CellServDB only at startup? Can it be forced to
> re-read it without a restart?
> 
> If a CellServDB contains multiple entries (4) for a given cell, does the
> client process them in any particular order (round robin, random, other)?
> If some are non-responsive, will the client give preference to the others?

Look at fs newcell and fs setserverprefs.

-Ben