10.3. Customizing Overcloud Post-Configuration

A situation might occur where you have completed the creation of your Overcloud but want to add additional configuration, either on initial creation or on a subsequent update of the Overcloud. In this case, you use the OS::TripleO::NodeExtraConfigPost resource to apply configuration using the standard OS::Heat::SoftwareConfig types. This applies additional configuration after the main Overcloud configuration completes.
In this example, we first create a basic Heat template (/home/stack/templates/nameserver.yaml) that runs a script to append each node's resolv.conf with a variable nameserver. 
heat_template_version: 2014-10-16

description: >
  Extra hostname configuration

parameters:
  servers:
    type: json
  nameserver_ip:
    type: string
  DeployIdentifier:
    type: string

resources:
  ExtraConfig:
    type: OS::Heat::SoftwareConfig
    properties:
      group: script
      config:
        str_replace:
          template: |
            #!/bin/sh
            echo "nameserver _NAMESERVER_IP_" >> /etc/resolv.conf
          params:
            _NAMESERVER_IP_: {get_param: nameserver_ip}

  ExtraDeployments:
    type: OS::Heat::SoftwareDeployments
    properties:
      config: {get_resource: ExtraConfig}
      servers:  {get_param: servers}
      actions: ['CREATE','UPDATE']
      input_values:
        deploy_identifier: {get_param: DeployIdentifier}
In this example, the `resources` section contains the following:
ExtraConfig
This defines a software configuration. In this example, we define a Bash script and Heat replaces _NAMESERVER_IP_ with the value stored in the nameserver_ip parameter.
ExtraDeployments
This executes a software configuration, which is the software configuration from the ExtraConfig resource. Note the following:
  • The servers parameter is provided by the parent template and is mandatory in templates for this hook.
  • input_values contains a parameter called deploy_identifier, which stores the DeployIdentifier from the parent template. This parameter provides a timestamp to the resource for each deployment update. This ensures the resource reapplies on subsequent overcloud updates.
Next, create an environment file (/home/stack/templates/post_config.yaml) that registers our Heat template as the OS::TripleO::NodeExtraConfigPost: resource type. 
resource_registry:
  OS::TripleO::NodeExtraConfigPost: /home/stack/templates/nameserver.yaml

parameter_defaults:
  nameserver_ip: 192.168.1.1
To add the configuration, add the environment file to the stack when creating or updating the Overcloud. For example: 
$ openstack overcloud deploy --templates -e /home/stack/templates/post_config.yaml
This adds the configuration to all nodes after the core configuration completes on either initial Overcloud creation or subsequent updates.

Important

You can only register the OS::TripleO::NodeExtraConfigPost to only one Heat template. Subsequent usage overrides the Heat template to use.