load sharing

[Piercarlo Grandi]

On 6 Feb 91 16:22:07 GMT, pjw at usna.navy.mil, jw at math30, (Peter J.
Welcher (math FACULTY)) said:

pjw> The question is, is there any easy way to perform load-sharing,
pjw> other than by randomly assigning sections or students to hosts ?

fwp1 at CC.MsState.Edu (Frank Peters) writes:

fpw1> I once toyed with an idea to do something like this using DNS but
fpw1> never implemented it.

On 7 Feb 91 09:20:19 GMT, mfg at castle.ed.ac.uk (M Gordon) said:

mfg> I implemented a similar idea for our network of suns.  Named has
mfg> been altered to recognise "sun3" and "sun4" as special cases and
mfg> use RPC to get a hostname from a server.  There were several reaons
mfg> for doing it this way, rather than having named doing the polling
mfg> itself.

These are hacks, that may work or something like that. There are
actually two load sharing issues; one is directing logins to specific
hosts, another is directing commands to specific hosts.

The second is more interesting. There are some posted implementations of
shells that will probe various compute servers to find the least loaded
using rstatd and then call the rexecd daemon to remote execute the
comamdn on the least loaded host. One I think was done by George Goble
at Purdue; another by somebody at BTL and is posted in
comp.sources.unix.

A similar tool is extremely easy to write, a couple dozen lines. It is
possible to just use these couple dozen lines as a wrapper around most
large or frequently executed commands, or actually take a shell source
and stick them in in the section that invokes external commands. I think
that the heuristic of choosing the lowest load average host is not one
of the best, but at least is simple; I think that memory size and
whether the host has local or remote access to the files needed by the
command should be taken into account.

Doing a nice system that will execute each command, maybe described in
some profile file, on the most apropriate machine, is a nice research
project.

Directing logins is an easier exercise; usually, if one has remote
command execution as above, a simple rotor (FIFO) style policy will
suffice. Many rlogin boxes will do it automatically.
--
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