How to Render Jenkins Build Parameters Dynamically

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While working with Jenkins jobs (whether they're declarative or freestyle), we often need to pass some parameters to the code being executed when triggering the job. Jenkins supports this use-case by means of parameters that you can declare and use as Groovy variables in your Jenkins job. However, often you are not aware of all the parameters in the beginning, or sometimes you want to render the parameters dynamically based on the value selected in any other parameter. 

Given the declarative nature of Jenkins jobs, we cannot achieve the use-case with the native Jenkins parameters available. Here comes the Active Choices parameter plugin to the rescue, which can help us render parameter values dynamically.

Active Choices parameter plugin provides three types of parameters.

  1. Active Choices Parameter
  2. Active Choices Reactive Parameter
  3. Active Choices Reactive Reference Parameter

Let's discuss each of these parameters and what they do.

Active Choices Parameter

Active Choices Reactive Parameter

Active Choices Reactive Reference Parameter

Active Choices Use Cases

Active Choices Parameter

Used when we want to generate the dropdown of checkboxes dynamically via some value returned from the API. For example, we can make an API call to fetch all the country's states and return it as a Groovy list so they will be rendered as a dropdown list.

Active Choices Reactive Parameter

Used when we want to generate the dropdown of checkboxes based on the value returned from an API call plus selection in other dependent build parameters. Consider the above example of state, if we want to render all the cities for the state selected then we can use the Active Choices Reactive parameter and refer to the state parameter so that we can use the value of state parameter in the Groovy script for cities parameter.

Active Choices Reactive Reference Parameter

Think of a deployment pipeline for a three-tier application where we have to deploy multiple services for each tier. If we want the user to select which services they want to deploy along with the release tag for that service, we need one extra control to ask the user for the release tag for the service they have selected. We can achieve this using the Active Choices Reactive Reference Parameter, as it lets us render HTML components dynamically using some Groovy script. So, we can have a checkbox and textbox side-by-side which was not possible in earlier cases. A detailed explanation of the use case is available in the section titled "Render HTML inputs Control using Active Choices Reactive Reference Parameter."

Prerequisites

Render Values Dynamically Based on the Selection in Other Build Parameter

In this use case, we will see how to render a dropdown with dynamic values using Active Choices Reactive parameters. We will see how we can configure the Active Choices parameter and Active Choices Reactive parameter. 

Jenkins parameter configurations page.

Groovy
  
return ["Gujarat", "Maharashtra", "Punjab"]


Dropdown box on Build With Parameters page.

Now we will add an Active Choices Reactive Parameter, which will update the values based on the selection in the states parameter. We will render the cities for the states we rendered.

Demonstration on how to add the Active Choices Reactive Parameter.

Groovy
  
  if ( states == "Gujarat") {
    return ["Rajkot", "Ahmedabad", "Jamnagar"]
  } else if ( states == "Maharashtra") {=
    return ["Mumbai", "Pune", "Nagpur"]
  } else if (states == "Punjab") {=
    return ["Ludhiana", "Amritsar", "Jalandhar"]
  }


Here, we have referenced the states parameter and used its value in the Groovy script to render the values for the cities for that state. Now, hit the save button and click on "Build with Parameters."

It will look something like this on the "Build with Parameters" page. Based on the selection in the states dropdown list, the radio buttons will be updated.

GIF showing "Build with Parameters" dropdown in action.

Currently, none of the radio buttons are selected by default. If we want any radio button to be selected by default, we can add :selected after the value in the list. For example, If we wish Ahmedabad to be selected by default, then we will put something like this:

Groovy
  
if ( states == "Gujarat") {
  return ["Rajkot", "Ahmedabad:selected", "Jamnagar"]
} …


Accessing the Values in Pipeline

Now we will add a pipeline code to see the values of the parameters we have added. 

Click on the configure and scroll down to the Pipeline section and add the following script there.

Groovy
  
pipeline {
  agent any
  stages {
    stage('Demo Active Choices Parameter') {
      steps {
        echo "States Selected ${states}"
        echo "Cities Selected ${cities}"
      }
    }
  }
}


Save the configuration and click on the "Build with Parameters," select the state and city and click on "Build." The console output will be as below:

Shell
  
[Pipeline] {
[Pipeline] stage
[Pipeline] { (Demo Active Choices Parameter)
[Pipeline] echo
States Selected Gujarat
[Pipeline] echo
Cities Selected Ahmedabad
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS


In the above use-case, we used radio buttons for the cities; let’s change it to the checkboxes and see how it sets the multiple values as comma-separated values. We will go to the configure section and scroll down to the cities section, change the "Choice Type" to "Check Boxes" for the cities parameter, save and build the job with multiple cities selected, and check the console output.

Screenshot displaying new build parameters.

Look at the echo for cities. It has multiple city names separated by commas.

Shell
  
[Pipeline] Start of Pipeline
[Pipeline] node
Running on Jenkins in /var/lib/jenkins/workspace/tp
[Pipeline] {
[Pipeline] stage
[Pipeline] { (Demo Active Choices Parameter)
[Pipeline] echo
States Selected Gujarat
[Pipeline] echo
Cities Selected Rajkot,Ahmedabad,Jamnagar
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS


Render HTML Inputs Control Using Active Choices Reactive Reference Parameter

We will try to write a sample Jenkins pipeline to deploy selected services for a multi-tier application along with the release tag. We will render a dropdown list using Active Choices Parameter that will list down the tiers we have. And based on the selection of the tier, we will render the services, which will have a checkbox and a textbox where a user can pass a release tag for the service. We will render checkbox and textbox as HTML input controls.

GIF displaying "This project is paramaterized" checkbox.

Active Choices Reactive Reference Parameter preferences settings.

Groovy Script for rendering the HTML input controls dynamically:

Groovy
  
service_tier_map = [
  "web": [
    ["service_name": "user_frontend", "release_tag": "1.0.0" ],
    ["service_name": "admin_frontend", "release_tag": "1.0.2" ],
  ],
  "backend": [
    ["service_name": "admin_service", "release_tag": "2.1.0" ],
    ["service_name": "finance_service", "release_tag": "2.2.0" ],
    ["service_name": "payment_service", "release_tag": "3.2.0" ],
  ],
  "database": [
    ["service_name": "dynamo_db", "release_tag": "5.4.1"],
    ["service_name": "mysql", "release_tag": "3.2.1"],
    ["service_name": "postgresql", "release_tag": "1.2.3"],
  ],
]


html_to_be_rendered = "<table><tr>"
service_list = service_tier_map[tier]
service_list.each { service ->
  html_to_be_rendered = """
    ${html_to_be_rendered}
    <tr>
    <td>
    <input name=\"value\" alt=\"${service.service_name}\" json=\"${service.service_name}\" type=\"checkbox\" class=\" \">
    <label title=\"${service.service_name}\" class=\" \">${service.service_name}</label>
    </td>
    <td>
    <input type=\"text\" class=\" \" name=\"value\" value=\"${service.release_tag}\"> </br>
    </td>
    </tr>
"""
}

html_to_be_rendered = "${html_to_be_rendered}</tr></table>"

return html_to_be_rendered


Let’s take a look at how we render the HTML inputs. We have to be very careful about the HTML inputs and their syntax, as if we change some configuration around them, we will not be able to get the value of that input control in the Pipeline code.

How We Can Render the Textbox HTML Input

For textbox control, we can use the below syntax, we can update some values as per our use-case.

HTML
  
<input type="text" class=" " name="value" value="any-value">


Look at the name parameter for this HTML tag, we cannot change it, and it must be the same as mentioned here. If we change it, we will not be able to get the value of this textbox in the pipeline code.

How We Can Render the Checkbox HTML Input

For the checkbox control, we can use the below syntax. We can update some values as per our use case.

HTML
  
<input name="value" alt="checkbox-name" json="checkbox-name" type="checkbox" class=" ">


As we have seen for the textbox input, the name must be a value. Alt and JSON attributes are optional, but as we have multiple checkboxes in our use case, we need to use this parameter to identify which checkbox was checked. If we don’t pass the alt and JSON parameters, then the value for the checkbox will be seen as true in the pipeline code. But if we pass the alt and JSON, then the value of the checkbox will be seen as the string we passed in alt and JSON.

NOTE: We can see only selected checkboxes in the pipeline code, unselected ones will be ignored by the Jenkins. Also, alt and JSON parameters must have the same value for the checkbox.

Save the configuration and open the "Build with Parameter" page. It will be something like this:

View of the "Build with Parameter" page.

Pipeline Code to Access the Values

Let’s add the pipeline code to see the values in action. Open the "Configure Job" page, scroll down to the last item, and add the following script to the pipeline code text box:

Groovy
  
pipeline {
  agent any
  stages {
    stage('Demo Active Choices Parameter') {
      steps {
        echo "Tier Selected ${tier}"
        echo "Services Selected ${services}"
      }
    }
  }
}


Save the job and run the job by clicking on "Build with Parameters." Select the tier and services you want to deploy and click on "Build." I have run the job using the parameters below and the output for the same is mentioned below.

Sample build parameters.

Console output:

Shell
  
[Pipeline] {
[Pipeline] stage
[Pipeline] { (Demo Active Choices Parameter)
[Pipeline] echo
Tier Selected backend
[Pipeline] echo
Services Selected admin_service,2.1.0,2.2.0,payment_service,2.3.0,
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS


Let’s understand the output. The echo statement for the tier is straightforward. It prints whatever tier we have selected on the "Build with Parameters" page. 

The second echo statement that prints the build parameter services has comma-separated values for the HTML input controls we have rendered. We have provided the service_name in the alt and JSON field for the checkboxes, so for whichever checkboxes we selected, the name will be stored in the output. If we don't provide the alt and JSON field while rendering the HTML for the checkboxes, we will see the text “selected” instead of the name, and we will never be able to identify which checkbox was selected. 

For textboxes, it will print the value we have added to the input box. The order in which these values are printed is the same order in which the controls were rendered from the Groovy script. We can split this value based on commas and can deploy our services.

Conclusion

Jenkins declarative pipeline enables the ease of creating CI/CD for the various systems, but at the same time, the declarative nature of the pipeline becomes a headache when we want to render parameters dynamically. 

The Active Choices plugin helps to solve this problem by allowing us to render the parameter values and even the parameters dynamically by means of the Groovy and HTML code. This plugin is very simple to use as it needs just a basic level of understanding of Groovy and HTML.

 

 

 

 

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