Property Group

https://blueprints.launchpad.net/heat/+spec/heat-property-group

Adds PropertyGroup for grouping set of properties of a Heat Resource plug-in.

Problem description

In many of heat resource plug-in implementation, properties are getting defined with validation schema and there is no group concept exist which is required for following reasons:

  • some time, resource mandates to provide either PropertyA or PropertyB, and one of them is mandatory. This can’t be defined as of now in heat Properties schema, as developer can’t set required=true for both the properties and as part of validate() method, developer should implement the logic whether one of these property is provided.
  • some of the plug-in supports multiple versions of its thing, for example, docker plug-in supports multiple versions. so Some properties are only supported in some versions only. Now there is no generic way exist to specify declaratively that some properties are required for a given client version.

Proposed change

The first problem, could be solved by introducing the concept of PropertyGroup, which helps declarative validation as defined below:

Assume that there are two Properties PropertyA and PropertyB, and are already declared with proper Property Schema. Then Property Group could be defined as follows:

properties_schema: {
    PropertyA: {},
    PropertyB: {},
    ''' Here Either of these Properties are mandatory, but required=True
    can't be defined.'''
    property_groups: [
        group1: {
            properties:[PropertyA,PropertyB],
            operator: xor
        }
    ]
}

Here as part of ‘validation()’ phase, each of the groups in the property_groups will be validated in sequence by using the operator across properties. This helps to bring up the complex validation logic across dependent properties.

Each group declared in the property_groups can refer the other group in it’s properties list. so the complex validation could be:

property_groups: [
        group1: {
            properties:[PropertyA,PropertyB],
            operator: OR
        },
        group2: {
            properties:[PropertyC,PropertyD,group1],
            operator: AND
        },
    ]

Some time, a property or property_group will be depending on another property or property_group and this can be achieved by using ‘depends_on’ as one of the operator. Here operator are one of the binary operator supported by python.

Here, each of the property entry in the group’s properties field, could be defined in the form of

‘prp1.child_prp1.grand_child_prp1’.

where the first property in this pattern is depends on where property_groups is declared.

  • TOP-LEVEL-PROPERTY-GROUP: if property_groups is declared as top level entry in properties_schema, then first property in the pattern should be one of the top level property defined in the properties_schema.
  • ROOT-LEVEL-PROPERTY-GROUP:If its declared inside one of the property’s properties_schema then the first property is consider as one of its peer property name.

It will help developers to declare at appropriate place.

consider below properties_schema:

properties_schema = {
    ROLES: properties.Schema(
        properties.Schema.LIST,
        _('List of role assignments.'),
        schema=properties.Schema(
            properties.Schema.MAP,
            _('Map between role with either project or domain.'),
            schema={
                ROLE: properties.Schema(
                    properties.Schema.STRING,
                    _('Keystone role'),
                    required=True,
                    constraints=([constraints.
                                 CustomConstraint('keystone.role')])
                ),
                PROJECT: properties.Schema(
                    properties.Schema.STRING,
                    _('Keystone project'),
                    constraints=([constraints.
                                 CustomConstraint('keystone.project')])
                ),
                DOMAIN: properties.Schema(
                    properties.Schema.STRING,
                    _('Keystone domain'),
                    constraints=([constraints.
                                 CustomConstraint('keystone.domain')])
                ),
            }
        ),
        update_allowed=True
    )
}

Here either ROLE and PROJECT or ROLE and DOMAIN needs to provided for creating the role-assignment. But both PROJECT and DOMAIN can’t be declared with required=true. so property_groups could be defined as below:

TOP-LEVEL-PROPERTY-GROUP:

properties_schema = {
    ...
    property_groups: [
            role-project: {
                properties:[ROLES.ROLE,ROLES.PROJECT],
                operator: AND
            },
            role-group: {
                properties:[ROLES.ROLE, ROLES.GROUP],
                operator: AND
            },
            either-group: {
                properties:[property_groups.role-project,
                            property_groups.role-group],
                operator: OR
            }
        ]
}

ROOT-LEVEL-PROPERTY-GROUP

properties_schema = {
    ROLES: properties.Schema(
        properties.Schema.LIST,
        _('List of role assignments.'),
        schema=properties.Schema(
            properties.Schema.MAP,
            _('Map between role with either project or domain.'),
            schema={
                ...
                property_groups: [
                    role-project: {
                        properties:[ROLE, PROJECT],
                        operator: AND
                    },
                    role-group: {
                        properties:[ROLE, GROUP],
                        operator: AND
                    },
                    either-group: {
                        properties:[property_groups.role-project,
                                    property_groups.role-group],
                        operator: OR
                    }
                ]

            }
        ),
        update_allowed=True
    )
}

The second problem could be solved as follows: PropertyGroup can be used with ‘client_plugin_supported_since’ as follows:

property_groups: [
    group1: {
        properties:[PropertyA,PropertyB],
        operator: OR
        client_plugin_supported = [1.2]
    }
]

Heat engine can infer that this set of properties in the PropertyGroups are supported only from 1.2 version. so it can check the current client_plugin_supported and validate accordingly.

NOTE: property_groups is only declarative in resource plug-in implementation and it does not exposed in the template definition.

Alternatives

As implemented currently in each of the resource plug-in.

Implementation

Assignee(s)

Primary assignee:
Kanagaraj Manickam (kanagaraj-manickam) Peter Razumovsky <prazumovsky>

Milestones

Target Milestone for completion:
liberty-1

Work Items

  • Define PropertyGroup class with required validation logic for the given resource
  • Update the resource validation logic to validate with property group
  • Update the existing resources with property_groups.
  • Generate property group documentation for users to understand the property requirements.
  • Add required test cases

Dependencies

None.

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