[Feature request] client-level constraints

[Legogris]

There are many scenarios where one would like to ensure that a particular node only receives either a certain job(s) or task group(s). As I see it, there is no way of restricting nodes to particular job(s) or task group(s) without introducing constraints in some way on job definitions themselves (e.g. using meta or node_class). There are workarounds, for example restricting those jobs to use different drivers that are only used for those jobs, but that's more of a hacky workaround that will only work for certain cases.

It'd be great if the client stanza had some mechanism to whitelist certain jobs or task groups - be it by a constraint stanza, requiring certain meta fields, or even just a whitelist of job or task group names.

[tgross]

Hi @Legogris!

One way I've done this is to have those clients in a different datacenter (but still joined to the same set of servers). Because datacenter is already a required field in the jobspec, it gives you a very coarse-grained control.

[Legogris]

@tgross Thanks for the suggestion, that's not a bad idea. There's no impact to having this differ from consul dc for nomad clusters on consul, right?

[tgross]

There's no impact to having this differ from consul dc for nomad clusters on consul, right?

Right! A Consul datacenter is actually semantically closer to a Nomad region, so typically you'll end up with one Consul DC per Nomad region.

[pznamensky]

Nevertheless the "datacenter" workaround is not a good decision for all cases: #2299 (comment)