Creating policy enforcement rules¶

This article illustrates how you can create policy enforcement rules. For testing purposes, create rules that prohibit the creation of instances with the flavor with over 2048 MB of RAM following the procedure below.

Procedure:

Verify that you have configured your OpenStack environment as described in Setting up policy enforcement.

To create the predeploy_errors rule, run:

congress policy rule create murano_system "predeploy_errors(eid, obj_id, msg) :- murano:objects(obj_id, pid, type), murano:objects(eid, tid, \"io.murano.Environment\"), murano:connected(eid, pid), murano:properties(obj_id, \"flavor\", flavor_name), flavor_ram(flavor_name, ram), gt(ram, 2048), murano:properties(obj_id, \"name\", obj_name), concat(obj_name, \": instance flavor has RAM size over 2048MB\", msg)"

The command above contains the following information:

predeploy_errors(eid, obj_id, msg) :-
   murano:objects(obj_id, pid, type),
   murano:objects(eid, tid, "io.murano.Environment"),
   murano:connected(eid, pid),
   murano:properties(obj_id, "flavor", flavor_name),
   flavor_ram(flavor_name, ram),
   gt(ram, 2048),
   murano:properties(obj_id, "name", obj_name),
   concat(obj_name, ": instance flavor has RAM size over 2048MB", msg)

Policy validation engine checks the predeploy_errors rule, and rules referenced within this rule are evaluated by the Congress engine.

In this example, we create the rule that references the flavor_ram rule we create afterwards. It disables flavors with RAM more than 2048 MB and constructs the message returned to the user in the msg variable.

In this example we use data from policy murano which is represented by murano:properties. There are stored rows with decomposition of model representing murano application. We also use built-in functions of Congress:

gt stands for ‘greater-than’
concat joins two strings into one variable

To create the flavor_ram rule, run:
```
congress policy rule create murano_system "flavor_ram(flavor_name, ram) :- nova:flavors(id, flavor_name, cpus, ram)"
```
This rule resolves parameters of flavor by flavor name and returns the ram parameter. It uses the flavors rule from nova policy. Data in this policy is filled by the nova datasource driver.
Check the rule usage.
1. Create an environment with a simple application:
  - Select an application from the murano applications.
  - Create a m1.medium instance, which uses 4096 MB RAM.
2. Deploy the environment.