THT design patterns

Duplicated parameters

Problem: When defining multiple related services, it can be necessary to define the same parameters (such as rabbit or DB credentials) in multiple service templates. To avoid this, it is possible to define a “base” heat template that contains the common parameters and config_settings mapping for those services that require it.

This pattern will describe how to avoid duplicated parameters in the THT yaml files.

mongodb-base.yaml: This file should have all the common parameters between the different environments (With pacemaker and without pacemaker).

heat_template_version: 2016-04-08
description: >
  Configuration details for MongoDB service using composable roles
parameters:
  MongoDbNoJournal:
    default: false
    description: Should MongoDb journaling be disabled
    type: boolean
  MongoDbIPv6:
    default: false
    description: Enable IPv6 if MongoDB VIP is IPv6
    type: boolean
  MongoDbReplset:
    type: string
    default: "tripleo"
outputs:
  role_data:
    description: Role data for the MongoDB base service.
    value:
      config_settings:
        mongodb::server::nojournal: {get_param: MongoDbNoJournal}
        mongodb::server::ipv6: {get_param: MongoDbIPv6}
        mongodb::server::replset: {get_param: MongoDbReplset}

In this way we will be able to reuse the common parameter among all the template files requiring it.

Referencing the common parameter:

mongodb.yaml: Will have specific parameters to deploy mongodb without pacemaker.

heat_template_version: 2016-04-08
description: >
  MongoDb service deployment using puppet
parameters:
  #Parameters not used EndpointMap
  EndpointMap:
    default: {}
    description: Mapping of service endpoint -> protocol. Typically set
                 via parameter_defaults in the resource registry.
    type: json
resources:
  MongoDbBase:
    type: ./mongodb-base.yaml
outputs:
  role_data:
    description: Service mongodb using composable services.
    value:
      config_settings:
        map_merge:
          - get_attr: [MongoDbBase, role_data, config_settings]
          - mongodb::server::service_manage: True
      step_config: |
        include ::tripleo::profile::base::database::mongodb

In this case mongodb.yaml is using all the common parameter added in the MongoDbBase resource.

If using the parameter ‘EndpointMap’ in the base template, you must the pass it from from the service file, and even if it is not used in the service template, it must still be defined.

In the service file:

parameters:
  EndpointMap:
    default: {}
    description: Mapping of service endpoint -> protocol. Typically set
                 via parameter_defaults in the resource registry.
    type: json
resources:
  <ServiceName>ServiceBase:
    type: ./<ServiceName>-base.yaml
    properties:
      EndpointMap: {get_param: EndpointMap}

This will pass the endpoint information to the base config file.

Note

Even if the EndpointMap parameter is optional in the base template, for consistency is advised always using it in all service templates.