Parameter Constraints

The constraints block of a parameter definition defines additional validation constraints that apply to the value of the parameter. The parameter values provided by a user are validated against the constraints at instantiation time. The constraints are defined as a list with the following syntax

constraints:
  - <constraint type>: <constraint definition>
    description: <constraint description>

constraint type

Type of constraint to apply. The set of currently supported constraints is given below.

constraint definition

The actual constraint, depending on the constraint type. The concrete syntax for each constraint type is given below.

description

A description of the constraint. The text is presented to the user when the value he defines violates the constraint. If omitted, a default validation message is presented to the user. This attribute is optional.

The following example shows the definition of a string parameter with two constraints. Note that while the descriptions for each constraint are optional, it is good practice to provide concrete descriptions to present useful messages to the user at deployment time.

parameters:
  user_name:
    type: string
    label: User Name
    description: User name to be configured for the application
    constraints:
      - length: { min: 6, max: 8 }
        description: User name must be between 6 and 8 characters
      - allowed_pattern: "[A-Z]+[a-zA-Z0-9]*"
        description: User name must start with an uppercase character

The following sections list the supported types of parameter constraints, along with the concrete syntax for each type.

custom_constraint

The custom_constraint constraint adds an extra step of validation, generally to check that the specified resource exists in the backend. Custom constraints get implemented by plug-ins and can provide any kind of advanced constraint validation logic.

The syntax of the custom_constraint constraint is

custom_constraint: <name>

The name attribute specifies the concrete type of custom constraint. It corresponds to the name under which the respective validation plugin has been registered in the Orchestration engine.

For example

parameters:
  key_name
    type: string
    description: SSH key pair
    constraints:
      - custom_constraint: nova.keypair

The following section lists the custom constraints and the plug-ins that support them.