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StyleBook to create a basic load balancing configuration

December 31, 2023
Contributed by: 
C

In the previous example, you have built a basic StyleBook to create a load balancing virtual server. You can save this StyleBook with a different name and then update it to include additional parameters and components for a basic load balancing configuration. Save this StyleBook file as basic-lb-config.yaml.

In this section, you will design a new StyleBook that creates a load balancing configuration comprising of load balancing virtual server, a service group, and a list of services. It also binds the services to the service group and binds the service group to the virtual server.

To build this StyleBook, you have to start by updating the header section. This section is similar to the one you created for load balancing virtual server StyleBook. In the header section, change the value of name to basic-lb-config. Also, update description and display-name to describe this StyleBook appropriately. You do not have to change the namespace and version values. Because you have changed the name, the combination of name, namespace, and version creates a unique identifier for this StyleBook in the system.

name: basic-lb-config
description: This StyleBook defines a simple load balancing configuration.
display-name: Load Balancing Configuration
namespace: com.example.stylebooks
schema-version: "1.0"
version: "0.1"
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Import StyleBooks

The import-stylebooks section remains the same. It refers to the netscaler.nitro.config namespace to use the Nitro configuration objects.

import-stylebooks:
 -
 namespace: netscaler.nitro.config
 prefix: ns
 version: "10.5"
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Parameters

You have to update the parameters section to add two additional parameters to define the list of services or servers and the port on which the services listen to. The first three parameters, name, ip, and lb-alg remain the same.

parameters:
 -
 name: name
 type: string
 label: Application Name
 description: Name of the application configuration
 required: true
  -
   name: ip
   type: ipaddress
   label: Application Virtual IP (VIP)
   description: Application VIP that the clients access
   required: true
  -
   name: lb-alg
   type: string
   label: LoadBalancing Algorithm
   description: Choose the load balancing algorithm used for load balancing client requests between the application servers.
     allowed-values:
     - ROUNDROBIN
     - LEASTCONNECTION
      default: ROUNDROBIN
  -
   name: svc-servers
   type: ipaddress\[\]
   label: Application Server IPs
   description: The IP addresses of all the servers of this application
   required: true
  -
   name: svc-port
   type: tcp-port
   label: Server Port
   description: The TCP port open on the application servers to receive requests.
   default: 80
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In this example, the parameter svc-servers is added to accept a list of IP addresses of the services that represent the backend servers of the application. This is a mandatory parameter as indicated by required: true. The second parameter, svc-port, denotes the port number on which the servers listen. The default port number is 80 for svc-port parameter, if it is not specified by the user.

Components

You have to also update the components section to define additional components such that they use the two new parameters and build the complete load balancing configuration.

For this example, you have to write the components section as follows:

components:
 -
  name: lbvserver-comp
  type: ns::lbvserver
  properties:
   name: $parameters.name + "-lb"
   servicetype: HTTP
   ipv46: $parameters.ip
   port: 80
   lbmethod: $parameters.lb-alg

components:
 -
  name: svcg-comp
  type: ns::servicegroup
  properties:
   name: $parameters.name + "-svcgrp"
   servicetype: HTTP
  
components:
 -
  name: lbvserver-svg-binding-comp
  type: ns::lbvserver\_servicegroup\_binding
  properties:
   name: $parent.parent.properties.name
   servicegroupname: $parent.properties.name
 -
  name: members-svcg-comp
  type: ns::servicegroup\_servicegroupmember\_binding
  repeat: $parameters.svc-servers
  repeat-item: srv
  properties:
   ip: $srv
   port: str($parameters.svc-port)
   servicegroupname: $parent.properties.name
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In this example, the original component lbvserver-comp (from the previous example) now has a child component called svcg-comp. And, the svcg-comp component has two child components within it. Nesting a component within another component allows the nested component to create configuration objects by referring to attributes in the parent component. The nested component can create one or more objects for each object created in the parent component.

The svcg-comp component is used to create a service group on the Citrix ADC instance by using the values provided for the attributes of the resource “servicegroup”. In this example, you are specifying static value for servicetype, while name gets its value from the input parameter. You refer to the parameter name defined in the parameters section by using $parameters.name + “-svcgrp” notation, where -svcgrp is appended (concatenated) to the user-defined name.

The component svcg-comp has two child components, lbvserver-svg-binding-comp and members-svcg-comp.

The first child component, lbvserver-svg-binding-comp, is used to bind a configuration object between the service group created by its parent component and the load balancing virtual server (lbvserver) created by the parent’s parent component. The $parent notation, also called the parent reference, is used to refer to entities in the parent components. For example, servicegroupname: $parent.properties.name refers to the service group created by the parent component svcg-comp, and name: $parent.parent.properties.name refers to the virtual server created by the parent’s parent component lbvserver-comp.

The members-svcg component is used to bind configuration objects between the list of services to the service group created by the parent component. The creation of multiple binding configuration objects is achieved by using the repeat construct of StyleBook to iterate over the list of servers specified in the parameter svc-servers. During the iteration, this StyleBook component creates a Nitro configuration object of type servicegroup_servicegroupmember_binding for each service (referred to as srv in the repeat-item construct) in the service group, and it sets the ip attribute in each Nitro configuration object to the IP address of the corresponding server.

Generally, you can use the repeat and repeat-item constructs in a component to make that component build multiple configuration objects of the same type. You can assign a variable name to the repeat-item construct, for example, srv, to designate the current value in the iteration. This variable name is referred to in the properties of the same component or in child components as $<varname>, for example $srv.

In the above example, you have used nesting of components inside each other to easily construct this configuration. In this particular case, nesting of components was not the only way of building the configuration. You could have achieved the same result without nesting, as shown below:

components:
 -
  name: members-svcg-comp
  type: ns::servicegroup\_servicegroupmember\_binding
  repeat: $parameters.svc-servers
  repeat-item: srv
  properties:
   ip: $srv
   port: str($parameters.svc-port)
   servicegroupname: $components.svcg-comp.properties.name
 -
  name: lbvserver-svg-binding-comp
  type: ns::lbvserver\_servicegroup\_binding
  properties:
   name: $components.lbvserver-comp.properties.name
   servicegroupname: $components.svcg-comp.properties.name
 -
  name: lbvserver-comp
  type: ns::lbvserver
  properties:
   name: $parameters.name + "-lb"
   servicetype: HTTP
   ipv46: $parameters.ip
   port: 80
   lbmethod: $parameters.lb-alg
 -
  name: svcg-comp
  type: ns::servicegroup
  properties:
  name: $parameters.name + "-svcgrp"
  servicetype: HTTP  
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Here, all the components are at the same level (that is, they are not nested) but the result achieved (the Citrix ADC configuration generated) is the same as that of the nested components used earlier. Also, the order in which the components are declared in the StyleBook does not impact the order of creation of the configuration objects. In this example, the components svcg-comp and lbvserver-comp, even though declared last, must be built before building the second component lbvserver-svg-binding-comp because there are forward references to these components in the second component.

Note

By convention, the names of StyleBooks, parameters, substitutions, components and outputs are in lowercase. When they contain multiple words, they are separated by a “-“ character. For example “lb-bindings”, “app-name”, “rewrite-config”, and so on. Another convention is to suffix component names with “-comp” string.

Outputs

The last section you can add to the new StyleBook is the outputs section where you specify what this StyleBook exposes to its users (or in other StyleBooks) after it is used to create a configuration. For example, you can specify in the outputs section to expose the lbvserver and the servicegroup configuration objects that would be created by this StyleBook.

outputs:
 -
  name: lbvserver-comp
  value: $components.lbvserver-comp
  description: The component that builds the Nitro lbvserver configuration object
 -
  name: servicegroup-comp
  value: $components.svcg-comp
  description: The component that builds the Nitro servicegroup configuration object
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The outputs section of a StyleBook is optional. A StyleBook does not need to return outputs. However, by returning some internal components as outputs, it allows any StyleBooks that import this StyleBook more flexibility as you can see when creating a composite StyleBook.

Note

It is a good practice to expose an entire component of the StyleBook in the outputs section, rather than just a single property of a component (for example, expose the whole $components.lbvserver-comp rather than just the name $components.lbvserver-comp.properties.name). Also add a description to the output explaining what the specific output represents.

Build your StyleBook

Now that you have defined all the required sections of this StyleBook, bring them all together to build your second StyleBook. You have already saved this StyleBook file as basic-lb-config.yaml. Citrix recommends that you use the built-in YAML validator in StyleBooks page to validate and import the YAML content.

The full content of the file basic-lb-config.yaml is reproduced below:

name: basic-lb-config
namespace: com.example.stylebooks
version: "0.1"
display-name: Load Balancing Configuration
description: This StyleBook defines a simple load balancing configuration.
schema-version: "1.0"

import-stylebooks:
 -
  namespace: netscaler.nitro.config
  version: "10.5"
  prefix: ns
parameters:
 -
  name: name
  type: string
  label: Application Name
  description: Give a name to the application configuration.
  required: true
 -
  name: ip
  type: ipaddress
  label: Application Virtual IP (VIP)
  description: The Application VIP that clients access
  required: true
 -
  name: lb-alg
  type: string
  label: LoadBalancing Algorithm
  description: Choose the loadbalancing algorithm (method) used for loadbalancing client requests between the application servers.
  allowed-values:
     - ROUNDROBIN
     - LEASTCONNECTION
  default: ROUNDROBIN
 -
  name: svc-servers
  type: ipaddress[]
  label: Application Server IPs
  description: The IP addresses of all the servers of this application
  required: true

components:
 -
  name: lbvserver-comp
  type: ns::lbvserver
  properties:
   name: $parameters.name + "-lb"
   servicetype: HTTP
   ipv46: $parameters.ip
   port: 80
   lbmethod: $parameters.lb-alg
 -
  name: svcg-comp
  type: ns::servicegroup
  properties:
    servicegroupname: $parameters.name + "-svcgrp"
    servicetype: HTTP
  
 -
  name: lbvserver-svg-binding-comp
  type: ns::lbvserver_servicegroup_binding
  properties:
   name: $components.lbvserver-comp.properties.name
   servicegroupname: $components.svcg-comp.properties.servicegroupname
 -
  name: members-svcg-comp
  type: ns::servicegroup_servicegroupmember_binding
  repeat: $parameters.svc-servers
  repeat-item: srv
  properties:
   ip: $srv
   port: 80
   servicegroupname: $components.svcg-comp.properties.servicegroupname
outputs:
-
  name: lbvserver-comp
  value: $components.lbvserver-comp
  description: The component that builds the Nitro lbvserver configuration object
-
  name: servicegroup-comp
  value: $components.svcg-comp
  description: The component that builds the Nitro servicegroup configuration object
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To start using your StyleBook to create configurations, you have to import it to Citrix ADM and then use it. For more information, see How to Use User-Defined StyleBooks.

You can also import this StyleBook into other StyleBooks and use its properties as described in the next section.

StyleBook to create a basic load balancing configuration
December 31, 2023
Contributed by: 
C
December 31, 2023
Contributed by: 
C

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