Parameter Override

By default, parameters created in a parent, or root project, are automatically inherited in any child projects along with the parent's environment values. CloudTruth provides the ability to override parameters in situations where the child project might require different environment values. This essentially blocks inheritance from the parent project as if the parameter were created at the child project. We discuss inheritance further in the Parameter and Parameter Value Inheritance section.

In container-based applications, we might start with a top-level 'common' project to hold parameters which apply to all or some number of services. If we wanted to make sure every service started with a certain number of container, we could create a root-level project parameter named container_count and set with a reasonable value. This would ensure that every service configuration is set with a default container count which in turn makes for a valid configuration. Of course not all services are created equal, so some services may need a container count which is larger or lower than the default. Parameter override gives us the flexibility to generate valid configurations by default, then tweak each service as needed where a majority of the services would use the default value. Here's a simple example of how this would work:

Set a 'common' default value:

Parent project with default parameter value set

Child project inheriting the parent parameter and parameter value

Any new projects created under the 'common' parent automatically inherits the parents parameters and their values:

Create a new project as a child of the 'common' project

Child project listed under parent

New child project indicating parameter is inherited from parent

Overriding a Parameter:

1. Starting from parameter list in the child project (api), click the selector to the right of the parameter and choose Override Parameter, this will immediately open the OVERRIDE PARAMETER modal:

Inherited parameter selection menu

2. Here you can make any adjustments to the RULES or parameter EXPIRES options if needed:

3. Click Override Parameter, this will display the parameter detail page for the overridden parameter:

4. Notice this is the same as any other parameter with some details on where this parameter obtained the original value. Here we've adjusted the overridden parameter's default environment value:

5. At this point, it may make sense to adjust any environment values for this service. In most cases, the development environment may not need the adjustments required by the staging and production environments. This adjustment can be made by selecting the development environment in the ENVIRONMENTS tree, clicking Edit Value, then saving the new value. We'll discuss Value Overrides in the next section.

Parameter detail page showing overridden parameter

Although not as common as overriding environments, overriding a parameter in a child project can help shape the CloudTruth project tree to closely match the organizations app's and services. Keeping the configuration as DRY as possible by leaving us with sane defaults for the most reused parameters, then making adjustments as needed without disrupting others.

Removing a Parameter Override

Removing a parameter override can be accomplished from either the project's parameter list or from the parameter details page:

Parameter detail page showing overridden parameter

1. Click the selector to the right of the parameter and choose Remove Parameter Override:

2. A confirmation modal will appear, click Yes, remove to complete the override removal:

Removing an override will reset inheritance for the previously overridden parameter. It will now inherit all environment values and attributes from the parent project's instance of the parameter.