Asking for specific rabbits in jobspec

[jameshcorbett]

Marty has been adding some --requires=hosts constraints to his jobspecs to force flux to pick compute nodes associated with specific rabbits. However, it would be more ergonomic to simply specify the rabbits desired, since that's a much more compact representation. Something like --requires=hosts:rabbit203 to cause the scheduler to only choose compute nodes on the same rack as rabbit203.

[grondo]

I'm more just thinking out loud here, but --requires=hosts:rabbit203 would only work (I think) if constraining the resource graph to only vertexes that match a "hostname" of rabbit203 would result in something that could match the rest of the job request. (Given that I have no idea how the datawarp/rabbit matches work in Fluxion, I could be way off here)

An alternative would be to establish a new requires scheme rabbits which, when used (e.g. as --requires=rabbbits:rabbit203), would activate a custom rabbit constraint that would constrain the graph to only the resources with access or that would use the specified rabbits. A drawback to this is that there is no way that I know of to extend the constraints supported by Fluxion at the moment.

I just thought I'd bring these points up in case they were helpful. If the hosts solution works then that might be preferable.