Support YAQL function

Include the URL of your launchpad blueprint:

https://blueprints.launchpad.net/heat/+spec/yaql-function

This blueprint adds support of YAQL to heat.

Problem description

https://github.com/openstack/yaql

YAQL (Yet Another Query Language) is an embeddable and extensible query language, that allows performing complex queries against arbitrary objects.

Heat currently does not have the ability to evaluate complex expressions, such as:

  • Select values for a key from a list of dictionary.
  • Filter the list where one or more fields match condition(s).
  • Transform a list to dictionary or vice versa.
  • Simple arithmetic.
  • Evaluation of boolean logic.
  • Any combination of select, filter, transform, and evaluate.

Proposed change

This spec proposes to add yaql function to the heat of the such form:

yaql:
  expression: <expression>
  data:
      <var1>: <val1>
      ...

Where expression is a valid yaql expression that will be evaluated, data is a dictionary with variables to which we can refer from the expression.

Referencing to corresponding data:

outputs:
  o1:
    value: {yaql: {expression: $.data.foo, data: {foo: 1}}}

o1 will be evaluated to 1

Expression evaluation:

parameters:
  list_param:
    type: comma_delimited_list
    default: [1, 2, 3]
  bool_param1:
    type: boolean
    default true
  bool_param2:
    type: boolean
    default: false
resources:
  asg:
    type: OS::Heat::AutoscalingGroup
    properties:
      resource:
        type: OS::Nova::Server
        ...
  rg:
    type: OS::Heat::ResourceGroup
    properties:
      count: 3
      type: child.yaml
      properties:
        index: "%index%"
        ...
outputs:
  o1:
    yaql:
      expression: $.data.bool_param1 and $.data.bool_param2
      data:
        bool_param1: {get_param: bool_param1}
        bool_param2: {get_param: bool_param2}
  o2:
    yaql:
      expression: $.data.list_param.select(int($)).max()
      data:
        list_param: {get_param: list_param}
  o3:
    yaql:
      expression: int($.data.list_param[0]) + int($.data.list_param[1]))
      data:
        list_param: {get_param: list_param}
  o4:
    yaql:
      expression: $.values().where($.status="FAILED").select($.id)
      data: {get_attr: [asg, outputs, show]}

The content of child.yaml:

parameters:
  nova_flavors:
    type: comma_delimited_list
    default: [m1.tiny, m1.small, m1.large]
  index:
    type: string
resources:
  instance:
    type: OS::Nova::Server
    properties:
      ...
      flavor:
        yaql:
          expression: $.data.nova_flavors[
            int($.data.index) mod $.data.nova_flavors.len()]
          data:
            nova_flavors: {get_param: nova_flavors}
            index: {get_param: index}

o1 will be evaluated to false, o2 will be evaluated to 3, o3 will be evaluated to 3, o4 will contain a list os servers id that are in failed state, 3 servers with m1.tiny, m1.small, m1.large flavors will be created.

Add 2 config options for bounding of yaql:

limit_iterators that defines maximum number of elements in collection that expression can take for its evaluation, and

memory_quota that defines maximum size of memory in bytes that expression can take for its evaluation.

Alternatives

None.

Implementation

Assignee(s)

Primary assignee:
ochuprykov@mirantis.com

Milestones

newton-1

Work Items

  1. Implement yaql intrinsic function.
  2. Add related tests.
  3. Add corresponding docs.
  4. Add examples of usage to heat-templates.

Dependencies

None

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