Properties Group

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

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

Problem description

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

  • sometimes, resource mandates to provide either PropertyA or PropertyB, and one of them is mandatory. This can’t be defined 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 plug-ins supports multiple versions of its thing, for example, docker plug-in supports multiple versions. So some properties are only supported in specific versions only. Now there is no generic way 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 PropertiesGroup, which helps declarative validation as defined below:

Resource class will have properties_groups_schema, which contains list of properties groups. Each properties group has next representation:

Assume that there are two Properties: PropertyA and PropertyB, and there are already declared with proper Property Schema. Then properties group will be specified by logical expression in dict:

properties_groups_schema = [
    {properties_group.AND: [[PropertyA], [PropertyB]]}
]

In that way, logical expression consists of one-key dict with list-type value, which can contain list-type properties names or properties group logical expression. Dictionary key should be equal to one of the following operators: “and”, “or”, “xor”.

Properties groups can be nested, for example:

properties_groups_schema = [
    {properties_group.AND: [
        {properties_group.OR: [[PropertyA], [PropertyB]]},
        [propertyC]]}
]

Here as part of ‘validation()’ phase, each of the groups in the property_groups_schema 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 properties_groups_schema can refer the other group in it’s properties list. So the complex validation could be:

Here, each of the property entry could be defined in the form of

[‘prp1’, ‘child_prp1’, ‘grand_child_prp1’]

even if property entry comprises only one item, i.e.

[‘prp1’]

For example, if there’s properties_schema:

properties_schema = {
    PropertyA: properties.Schema(
        properties.Schema.MAP,
        schema={
            PropertySubA: properties.Schema(properties.Schema.STRING),
            PropertySubB: properties.Schema(properties.Schema.STRING)
        }
    )
}

Then properties_groups_schema should be next:

properties_groups_schema = [
    {properties_group.AND: [[PropertyA, PropertySubA],
                            [PropertyA, PropertySubB]]}
]

Also, properties group will support specifying API versions of client_plugin, used for property, i.e. property will be supported only if specified client_plugin API version satisfies versions in group. Then property group will have next format:

properties_groups_schema = [
    {properties_group.API_VERSIONS: {
        properties_group.CLIENT_PLUGIN: <client_plugin object>,
        properties_group.VERSIONS: <list of supported versions>,
        properties_group.PROPERTIES: <list of properties entries>}
    }
]

Example of using API_VERSIONS as properties group:

properties_groups_schema = [
    {properties_group.API_VERSIONS: {
        properties_group.CLIENT_PLUGIN: self.client_plugin('keystone'),
        properties_group.VERSIONS: ['1.2', '2.0'],
        properties_group.PROPERTIES: [[PropertyA], [PropertyB]]}
    }
]

Heat engine can infer that this set of properties in the properties group is supported only for 1.2 and 2.0 API versions, so it can check the current client_plugin supported and validate accordingly.

Besides the validation part, all necessary changes will be added to documentation generator to allow user learn relations between properties.

Alternatives

None.

Implementation

Assignee(s)

Primary assignee:

Kanagaraj Manickam (kanagaraj-manickam)

Peter Razumovsky <prazumovsky>

Milestones

Currently moved to backlog due to no community’s interest. Workable PoC placed here:

https://review.openstack.org/#/q/topic:bp/property-group

Work Items

  • Define PropertiesGroup 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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