Add user specific quotas

[RobinFrcd]

Hi,
I've added two configuration parameters:

• user_without_quotas will overwrite mem_limit/cpu_limit. Users in this
  list will have unlimited RAM and CPU.

• special_user_quotas will overwrite mem_limit and cpu_limit for a
  specific user. It is possible to set mem_limit OR/AND cpu_limit.

user_without_quotas  = {'user1', 'user2'}
special_user_quotas = {
    'user3': {
        'mem_litmit': '2G'
    },
    'user4': {
        'mem_limit': '4G',
        'cpu_limit: 1.5
    }
}

user_without_quotas is stronger than special_user_quotas.

Hope it will be useful.

[RobinFrcd]

/cc @yuvipanda for his opinion

[yuvipanda]

(thank you for the patch! I'll look into this sometime within the next week!)

Also cc @minrk for his thoughts, if he has time to spare.

[willingc]

Thanks for the PR @RobinFrcd. Some small suggestions for now. Probably should add in the unlimited help text that by setting unlimited to true that the user could use all the resources of the cluster.

[willingc]

Hi and thanks for the PR :-)

Perhaps this would be better as a Bool similar to https://github.com/jupyterhub/jupyterhub/blob/master/jupyterhub/app.py#L453

[RobinFrcd]

So, in that case, we would enable this 'no quotas mode' for all user in the admin group ? So you want to check that the user is in Authenticator.admin_users and that users_without_quotas is True ?

[willingc]

Sorry @RobinFrcd. I didn't mean to confuse. The overarching point that I'm trying to make (though not eloquently) is that any time a user (admin or otherwise) has the ability to use all the resources that should be an opt-in action instead of the default.

[RobinFrcd]

Well, if a user is in users_without_quotas he has the ability to use all the resources. If he's not in, he can't. So the default is that a user can't use all the resources. I think I don't get the point here ! :)

[willingc]

Let's put the help in triple quotes. help="""Dict with...

[astro-arphid]

Is this something that's still a possibiltiy? The abilitiy to have different resource limits on a user or group level would be fantastic.

[consideRatio]

This seems like a very relevant feature, soo much that it should be relevant for other cases than quotas - such as user specific .

This is whats proposed in #98, I'll close this in favor of that.