Product Documentation

Dependency detection

May 24, 2018

Components in a StyleBook can refer to properties or sections of other components in the same StyleBook. Components are complete blocks by themselves and they may not be written in the same order that they have to be executed. The StyleBook compiler checks the order in which the components are written and then executes them in a logical order.

Example:

components:

  -

    name: lbvserver-comp

    type: ns::lbvserver

    properties:

      name: mylb

      ipv46: 10.102.190.15

      port: 80

      servicetype: HTTP

 -

    name: lb-sg-binding-comp

    type: ns::lbvserver_servicegroup_binding

    condition: $parameters.create-binding

    properties:

      name: $components.lbvserver-comp.properties.name

      servicegroupname: $components.sg-comp.properties.servicegroupname 

-

    name: sg-comp

    type: ns::servicegroup

    properties:

      servicegroupname: mysg

      servicetype: HTTP

In the above example, there are three components defined - lbvserver-comp, lb-sg-binding-comp, and sg-comp. When this StyleBook is executed, the lbvserver-comp is first created. The lb-sg-binding-comp refers to lbvserver-comp properties, but it cannot be created next though it is the second component defined in the StyleBook. This is because the lb-sg-binding-comp also has a dependency on the sg-comp which is yet to be created. As a result, the compiler reorders the components so that the dependencies of a component are resolved by the time a component is created, and executes this reordered list of components. The order of execution of the above StyleBook is: lbvserver-comp, sg-comp, and lb-sg-binding-comp.

Thus, the author of a StyleBook need not worry about the correct order of the components. The components may appear in any order. The compiler computes the correct order of execution of the components based on how the components refer each other. Note that this dependency detection and reordering also works for substitutions and outputs sections as well.

Cyclic Dependencies

Since a component may refer another component, it is possible that cycle of dependencies may be introduced in the definition of the StyleBook. For example, if component A refers to a property defined in component B, which again refers to a property defined in component A. This kind of dependency is called cyclic dependencies. Cyclic dependencies cannot be resolved automatically. The author of the StyleBook should manually correct the StyleBook definition to eliminate such cyclic dependencies. The compiler will be able to identify cyclic dependencies - if they exist, and report it.

The following example shows a cyclic dependency of components:

components:

  -

    name: lbvserver-comp

    type: ns::lbvserver

    properties:

      name: $components.lb-sg-binding-comp.properties.name

      ipv46: 10.102.190.15

      port: 80

      servicetype: HTTP

  -

    name: lb-sg-binding-comp

    type: ns::lbvserver_servicegroup_binding

    condition: $parameters.create-binding

    properties:

      name: mylb

      servicegroupname: $components.sg-comp.properties.servicegroupname

  -

    name: sg-comp

    type: ns::servicegroup

    properties:

      servicegroupname: mysg

      servicetype: $components.lbvserver-comp.properties.servicetype

In the above example, there are three components: lbvserver-comp, lb-sg-binding-comp, and sg-comp. lbvserver-comp depends on lb-sg-binding-comp, lb-sg-binding comp depends on sg-comp and sg-comp depends on lbvserver-comp. Here, a cycle of dependencies among these components is formed and this cannot be resolved automatically. As a result, this StyleBook cannot be executed. The StyleBook compiler detects this and prevents the StyleBook from being imported into NetScaler MAS.