Substitutions

The substitutions section is used to define shorthand names for complex expressions that can be used in the rest of the StyleBook to make reading the StyleBook easier. They are also useful when the same expression or value is repeated more than once in the StyleBook, for example, a constant value. Using a substitution name for this value allows you to update only the substitution value when this value needs to be changed rather than updating it at every location it appears in the StyleBook, which might be prone to error.

Substitutions are also used for defining mappings between values as described in examples later in this document.

Each substitution in the list is made up of a key and a value. The value can be a simple value, an expression, a function, or a map.

In the following example, two substitutions are defined. The first one is http-port that can be used as a shorthand for 8181. By using a substitution, you can refer to this in the rest of the StyleBook as $substitutions.http-port instead of 8181.

substitutions:

http-port: 8181

This allows you to specify a mnemonic name to a port number and define this port number in one place in the StyleBook, irrespective of the number of times it is used. If you want to modify the port number to 8080, you can modify it in the substitution section, and the change will take effect wherever the mnemonic name http-port is used. The following example shows how a substitution is used in a component.

components:

 -

     name: my-lbvserver-comp

     type: ns::lbvserver

     properties:

          name: $parameters.name + "-lb"

          servicetype: HTTP

          ipv46: $parameters.ip

          port: $substitutions.http-port

          lbmethod: $parameters.lb-alg
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