folks,
i wanted to draw on teh experience of this group.
my question has to do with models (or as strasser would have said,
ontologies).
when a higher-level tool tasked with maintaining 2 active web servers
notices that one has died, it has to pick a new node and start up the
web service there.
how does the tool know what requirements the web service needs? does
it share
an overall model with teh web service, so that it knows the concepts
of memory,
ports, etc? or does the tool essentially get a model from the web
service
and then paw through that to figure out what is needed?
it seems like there are just two answers:
a) there is a global model, populated by things like port numbers,
main memory,
cpu load, available disk space, firewalls and so on. all services can
state their requirements
and measure their usage and performance in terms (predicates etc) of
these entities.
b) the tool inherently knows nothing. it somehow discovers the
services extant in teh cluster
and then figures out what to do by grubbing around through teh
ontologies for each service.
so when the web service says it needs a port number as part of its
installation, the tool
finds the entity 'port number' as part of teh models belonging to the
'firewall' service
and the 'tcp/ip stack' service for a node.
it would be tempting to go with a), which is what i think the CIM
folks do.
even though it is a huge model, you can start small and it is fairly
straight forward
to compute what you need. it is work to extend the model, as you need
new code
to deal with structurally new things (as well as new bits of the model).
it would seem like b) is the most flexible and supportive of change,
having the least
impact on existing things when a new service (and model) is
introduced. but it is harder,
and if you thought bcfg2 or puppet specifications are a barrier to
adoption, just wait
til you see ontologies!
of course, if you are careful, you could code for b) while adopting
a) to start with...
so to restate, which answer a) or b) (or maybe another one) is the
best solution
for teh question of models for configuration management tools?
------------------
Andrew Hume (best -> Telework) +1 732-886-1886
[EMAIL PROTECTED] (Work) +1 973-360-8651
AT&T Labs - Research; member of USENIX and LOPSA
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