[Openstack-operators] Dynamic Policy
ayoung at redhat.com
Wed Aug 5 14:50:44 UTC 2015
How do you delegate the ability to delegate?
Lets say you are running a large cloud (purely hypothetical here) and
you want to let a user manage their own project. They are "admin" but
they should be able to invite or eject people.
In order to do this, an ordinary user needs to be able to make a role
assignment. However, Keystone does not support this today: if you are
admin somewhere, you are admin everywhere:
Access control in OpenStack is controlled by Policy. An informal survey
of operators shows that most people run with the stock policies such as
the Nova policy:
In order to scope admin to the proejct, we would need to have rules that
enforce this scoping: Evey rule should check that the project_id in the
token provided matches the project_id of the resource of the API.
If we manage to get the policy files rewritten this way, We then need a
way to limit what roles a user can assign. The default mechanism
would say that a user needs to have an administrative role on the
project (or domain) that they want to assign the role on.
I don't think anything I've written thus far is controversial. Then, why
has it not happened yet? here are the list of problems we need to solve:
1. Operators expect the existing policy files to work as is. Changing
them will break workflow.
2. If everything is scoped, we need a way to delete resources left
orphan when a project is deleted from Keystone and the service does not
get the notification (or know how to handle it).
Of the two, I think the top one is the more difficult to solve. Scoping
everything can be handled via one of two mechanism; either allow a
power-admin user to get a token scoped to some random project (even if
it has been deleted) or allow a token scoped to an administrative
project to also delete resources for a random project.
Dealing with the existing policy file issues is trickier, and that is
the real reason for the Dynamic Policy approach: give the endpoints
the ability to fetch their policy files from Keystone. If policy goes
from being a configuration file to data, it is managed outside of the
configuration management tools, and becomes much more fluid. This has
risks, and should be an Opt-In mechanism.
Fetching the policy files from Keystone also provides the start of a
richer set of management for policy rules. Currently, each of the stock
policy files exists only in their seperate git repos. There is no
sharing of policy rules across projects. If the policy files were
managed, rule by rule, from a centralized repository, rules could be
shared, providing, among other things, the ability to enforce
hierarchical roles, roles namespaced to a service, and other, richer
Feedback on this approach from operators is greatly appreciated. I need
to justify the effort that would go in to making this happen, so if you
want it, speak up.
If, on the other hand, you feel that this is needlessly complicated or
would make deployments more difficult, that is important too, and please
let me know.
Finally, if you can see some alternative methods of implementing a more
dynamic access control, please chime in.
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