How to Use Instance Roles

In NetScaler Management and Analytics System (MAS), there might be a scenario where you have to configure multiple Citrix ADC instances for a single application, but also where each ADC instance requires a different configuration to be deployed on them. An example of such a case is the default Microsoft Skype for Business StyleBook.

StyleBooks currently support the ability to create a configpack and apply the same configuration on multiple Citrix ADC instances. Such a scenario where the configuration is identical on all ADC instances, can be referred to as a symmetric configuration.

Now, with the “instance roles” feature of StyleBooks, you can create an asymmetrical configuration, that is, a configpack that can be applied on multiple ADC instances, but with different configurations on different ADC instances.

When a StyleBook with instance roles feature is used to create a configpack, each ADC instance in a configpack can be assigned a different role. This role determines the configuration objects of the configpack that the ADC instance will receive.

Points to note:

  • The set of instance roles in a StyleBook are defined while creating the StyleBook.
  • The roles are assigned to a specific ADC instance when creating or updating the configpack.

Target-roles section

A new section in a StyleBook called “target-roles” is introduced, where all the roles supported by the StyleBook are declared.

This section is typically placed after the “import-StyleBooks” section of a StyleBook, and before the parameters section.

In the following StyleBook example, two roles are defined in within the “target-roles” section - A and B.

target-roles:

  -
   name: A
   name: B
     min-targets: 2
     max-targets: 5

You can see that role B also defines two optional sub-properties, min-targets and max-targets.

Though these two sub-properties are optional, min-targets specify the minimum mandatory number of ADC instances that should be assigned this role when creating a configpack from this StyleBook, and max-targets specify the maximum number of ADC instances that can be assigned this role when creating a configpack from this StyleBook.

If these sub-properties are not specified, then there is no limit on the number of ADC instances that can be configured for that role. If min-targets = 0, the configuration associated with that role is optional and if min-targets = 1, then that configuration is mandatory and at least one ADC instance needs to be configured for that role.

Role “default”

In addition to explicitly defined roles, there is an implicit role that all StyleBooks have, and that role is called as a default role. This role can be used like any other role in a StyleBook. When creating a configpack, if an ADC instance is not assigned with a specific role, the instance gets implicitly assigned to the “default” role. The instance will now receive any configuration objects generated by components that have the “default” role.

Components with roles

After the roles that a StyleBook can support (including the role “default”) are defined, the roles can be used in the components section of a StyleBook. If you want a component to be deployed only on ADC instances that play a certain role, then you can specify the roles attribute as part of the component, as illustrated in the following example of a component:

  -
    name: C1
    type: ns::lbvserver
    roles:
      - A
    properties:
      name: lb1
      servicetype: HTTP
      ipv46: 1.1.1.1
      port: 80

In the above example, the component generates an “lbvserver” that will be deployed on instances playing the role A. Note that the roles attribute of a component is a list, and a component can be assigned multiple roles. These roles would have been declared in the “target-roles” section of the StyleBook.

Note: If a component in a StyleBook doesn’t specify a role attribute, then configuration objects generated by the component are created on all Citrix ADC instances regardless of their role. You can use this feature effectively to create configuration objects that can be applied to all instances of a configpack.

Let’s assume that there is a StyleBook with two roles defined - A and B, and which contains four components.

  • Component C1 has the roles A and B
  • Component C2 has the role B
  • Component C3 doesn’t have any roles defined
  • Component C4 has the role “default”

The components section of this StyleBook is reproduced below:

components:
  -
    name: C1
    type: ns::lbvserver
    roles:
      - A
      - B
    properties:
      name: lb1
      servicetype: HTTP
      ipv46: 1.1.1.1
      port: 80
  -
    name: C2
    type: ns::lbvserver
    roles:
      - B
    properties:
      name: lb2
      servicetype: HTTP
      ipv46: 12.12.12.12
      port: 80
  -
    name: C3
    type: ns::lbvserver
    properties:
      name: lb3
      servicetype: HTTP
      ipv46: 13.13.13.13
      port: 80
  -
    name: C4
    type: ns::lbvserver
    roles:
      - default
    properties:
      name: lb4
      servicetype: HTTP
      ipv46: 14.14.14.14
      port: 80

Note that the component C3 doesn’t have a role defined, which means the component is deployed on all instances regardless of their role. On the other hand, component C4 has the role “default”, which means it is applied to any instance that doesn’t have an explicit role assigned to it.

Now, consider that you want to create a configpack using this StyleBook, and deploy it on five ADC instances. At this stage, you can assign the roles to the instances in the following manner:

  • Role A is assigned to Instances T1, T2, T3 and T4
  • Role B is assigned to Instances T2, T3 and T4
  • Instance T5 is not assigned any role

The following image summarizes the role assignments, and shows the resulting configuration that each ADC instance will receive:

localized image

Note that component C3 is deployed on all instances regardless of role, since this component had no roles attribute.

The following image shows assignment of roles while creating a sample configpack:

localized image

You can also use the “Dry Run” feature when creating a configpack to view and verify the correct assignment of roles and the configuration objects that will be created on each ADC instance.

Build your StyleBook

The full content of the StyleBook “demo-target-roles” is provided below:

---
name: demo-target-roles
namespace: com.example.stylebooks
version: "1.2"
schema-version: "1.0"
import-stylebooks:
  -
    namespace: netscaler.nitro.config
    prefix: ns
    version: "10.5"
parameters:
  -
    name: appname
    type: string
    required: true
    key: true
target-roles:
  -
    name: A
  -
    name: B
    min-targets: 2
    max-targets: 5
components:
  -
    name: C1
    type: ns::lbvserver
    roles:
      - A
      - B
    properties:
      name: lb1
      servicetype: HTTP
      ipv46: 1.1.1.1
      port: 80
  -
    name: C2
    type: ns::lbvserver
    roles:
      - B
    properties:
      name: lb2
      servicetype: HTTP
      ipv46: 12.12.12.12
      port: 80
  -
    name: C3
    type: ns::lbvserver
    properties:
      name: lb3
      servicetype: HTTP
      ipv46: 13.13.13.13
      port: 80
  -
    name: C4
    type: ns::lbvserver
    roles:
      - default
    properties:
      name: lb4
      servicetype: HTTP
      ipv46: 14.14.14.14
      port: 80

The following image shows the objects created for a sample configpack:

localized image

Using APIs

When using the REST API, you can specify roles for each ADC instance when creating or updating the configpack as follows. In the “targets” block, specify the UUID of the specific Citrix ADC instance on which you want to deploy the individual components.

"targets": [
            {
             "id": "<ADC-UUID>",
             "roles": ["A"]
            },
           ]

A complete sample REST API is provided for your reference.

POST /<MAS-IP>/stylebook/nitro/v1/config/stylebooks/com.example.stylebooks/1.2/demo-target-roles/configpacks

{
  "configpack": {
     "parameters": {
     "appname": "app1"
    },
     "targets": [
        {
          "id": "f53c35c3-a6bc-4619-b4b4-ad7ab6a94ddb",
        "roles": ["A"]
        },
        {
          "id": "c08caa1c-1011-48aa-b8c7-9aed1cd38ed0",
          "roles": ["A", "B"]
        },
        {
          "id": "88ac90cb-a5cb-445b-8617-f83d0ef6174e",
          "roles": ["A", "B"]
        },
        {
          "id": "bf7b0f74-7a83-4856-86f4-dcc951d3141e",
          "roles": ["A", "B"]
        },
        {
          "id": "fa5d97ab-ca29-4adf-b451-06e7a234e3da",
          "roles": ["default"]
        }
      ]
    }
}
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How to Use Instance Roles