Register and Document Policy in Code

https://blueprints.launchpad.net/heat/+spec/policy-in-code

Operators need to maintain a (possibly complex) policy.json file that might differ only slightly from the default one, and some values in the policy.json file are tied to config options without explicit dependency between them.

Problem description

As an operator, I would like to specify in the policy.json file only those policies that are different from defaults.

Such support was declared as cross-project OpenStack community goal for Queens release [1].

Proposed change

Since version 1.9.0 oslo.policy supports handling policies in the way similar to how oslo.config handles config options [2]. Policies now can be declared inside Python code with provided defaults, and registered in the policy engine. The policy engine then loads these and the policy.json file on start, with entries in the latter overriding the defaults specified in the code.

This way, a service with default policies can run without policy.json file, and operators only need to fill this file in the case their rules are different.

Another nice benefit is that this allows to use values from config file in the default policy - as example, the name of the temporary user’s role in Heat currently is defined both in config file and default policy.json file, so operators need to update both heat.conf and policy.json file when changing this role.

A small performance penalty during service startup is expected, as well as marginal performance improvements during run-time, as there’s no need to re-read a possibly large policy.json file.

Sample policy file can be generated based on the registered policies rather than needing to manually maintain one.

A number of additional ways to generate policy-related files are supported by oslo.policy >= 1.10:

  • Merged policy file - a policy file can be generated which is a merge of registered defaults and policies loaded from a file. This shows the effective policy in use.
  • Redundant policies file - a list can be generated which contains policies defined in a file which match defaults registered in code. These are candidates for removal from the file in order to keep it small and understandable.

Heat already depends on oslo.policy >= 1.23 in its requirements, so no bump in dependencies is required.

Alternatives

None. Required to complete the cross-project goal.

Implementation

Assignee(s)

Primary assignee:
pshchelo <Pavlo Shchelokovskyy> IRC: pas-ha

Milestones

Target Milestone for completion:
queens-1

Work Items

  • accumulate, define and register policies in the Python code
  • change invocations of Enforcer.enforce to Enforcer.authorize (the call signature is unchanged)
  • amend genconfig tox environment to also generate sample policy.json file
  • remove policy.json file and update DevStack / Heat’s DevStack plugin to not use policy.json
  • (see dependencies) provide configs/scripts to generate merged policy file and redundant policy file.
  • amend documentation accordingly

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