Dynamic parameter values in Jenkins - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are dynamic parameter values in Jenkins?

Dynamic parameter values are values for build parameters that are generated or fetched at build time, allowing the parameters to change based on current data or environment.

intermediate

How can you create a dynamic choice parameter in Jenkins?

You can use the 'Active Choices Plugin' or 'Extended Choice Parameter Plugin' to create parameters whose options are generated by a script or external source at build time.

beginner

Which scripting languages are commonly used to generate dynamic parameter values in Jenkins?

Groovy is the most common scripting language used in Jenkins to generate dynamic parameter values because Jenkins supports Groovy scripts natively.

beginner

What is the benefit of using dynamic parameter values in Jenkins builds?

They allow builds to be more flexible and context-aware by providing up-to-date options, such as current branches, tags, or environment-specific values, improving automation and reducing manual errors.

intermediate

Give an example of a simple Groovy script to generate dynamic parameter values in Jenkins.

Example: return ['dev', 'test', 'prod'] This script returns a list of environment names as parameter options dynamically.

What plugin is commonly used to create dynamic choice parameters in Jenkins?

A Slack Notification Plugin

B Git Plugin

C Docker Plugin

D Active Choices Plugin

The Active Choices Plugin allows you to create parameters with dynamic values generated by scripts.

Which language is primarily used for scripting dynamic parameters in Jenkins?

A Groovy

B Bash

C Ruby

D Python

Groovy is the native scripting language supported by Jenkins for dynamic parameter generation.

Why use dynamic parameter values in Jenkins builds?

A To hardcode values for every build

B To disable parameters

C To provide up-to-date options based on current data

D To speed up the Jenkins UI

Dynamic parameters provide current and relevant options, improving build flexibility.

Which of these is NOT a typical source for dynamic parameter values?

A Current Git branches

B Static text files

C External APIs

D Build environment variables

Static text files are fixed and do not provide dynamic values.

What happens if a dynamic parameter script in Jenkins fails to run?

A The parameter list may be empty or cause an error

B The build proceeds with default values

C Jenkins restarts automatically

D The build is skipped silently

If the script fails, the parameter options may not load, causing errors or empty lists.

Explain how dynamic parameter values improve Jenkins build flexibility and give an example.

Think about how build choices can change over time.

Describe the steps to create a dynamic choice parameter in Jenkins using a Groovy script.

Focus on plugins and scripting.

Practice

1. What is the main purpose of using dynamic parameter values in Jenkins jobs?

easy

A. To update input options based on other inputs or external data

B. To make Jenkins jobs run faster

C. To disable user inputs during job execution

D. To automatically restart failed jobs

Solution

1. Step 1: Understand dynamic parameters

   Dynamic parameters change their available options based on other inputs or external data sources.

2. Step 2: Identify the purpose

   This makes Jenkins jobs flexible and user-friendly by showing relevant choices dynamically.

3. Final Answer:

   To update input options based on other inputs or external data -> Option A

4. Quick Check:

   Dynamic parameters update options dynamically [OK]

Hint: Dynamic parameters change options based on other inputs [OK]

Common Mistakes:

• Thinking dynamic parameters speed up job execution
• Confusing dynamic parameters with job restart features
• Assuming dynamic parameters disable inputs

2. Which Jenkins plugin is commonly used to create dynamic parameter values based on a script?

easy

A. Pipeline Plugin

B. Git Plugin

C. Active Choices Plugin

D. Mailer Plugin

Solution

1. Step 1: Identify plugins for dynamic parameters

   The Active Choices Plugin allows parameters to be dynamically generated using Groovy scripts.

2. Step 2: Exclude unrelated plugins

   Git Plugin manages source control, Pipeline Plugin manages job pipelines, and Mailer Plugin sends emails, none create dynamic parameters.

3. Final Answer:

   Active Choices Plugin -> Option C

4. Quick Check:

   Active Choices Plugin enables dynamic parameters [OK]

Hint: Active Choices Plugin supports scripted dynamic parameters [OK]

Common Mistakes:

• Choosing Git Plugin for dynamic parameters
• Confusing Pipeline Plugin with parameter plugins
• Selecting Mailer Plugin unrelated to parameters

3. Given this Groovy script for an Active Choices parameter:

return ['dev', 'test', 'prod'].findAll { it.startsWith(params.ENV_PREFIX ?: '') }

What will be the parameter options if ENV_PREFIX is set to t?

medium

A. ['dev', 'test', 'prod']

B. ['test']

C. ['prod']

D. []

Solution

1. Step 1: Understand the script filtering

   The script returns list items starting with the value of ENV_PREFIX. Here, ENV_PREFIX is 't'.

2. Step 2: Filter the list

   From ['dev', 'test', 'prod'], only 'test' starts with 't'.

3. Final Answer:

   ['test'] -> Option B

4. Quick Check:

   Filter by prefix 't' gives ['test'] [OK]

Hint: Filter list by prefix to find matching options [OK]

Common Mistakes:

• Ignoring the prefix filter and returning full list
• Choosing empty list when prefix matches an item
• Selecting wrong matching item

4. You wrote this Active Choices script:

return ['one', 'two', 'three'].filter { it.contains(params.SEARCH) }

But Jenkins shows a syntax error. What is the problem?

medium

A. The parameter SEARCH must be declared as a string

B. The list should be a map, not a list

C. The script must use double quotes for strings

D. The method should be findAll instead of filter

Solution

1. Step 1: Check Groovy list filtering methods

   Groovy uses findAll to filter lists, not filter which causes syntax error.

2. Step 2: Confirm other parts are correct

   The list syntax and parameter usage are valid; string quotes can be single or double.

3. Final Answer:

   The method should be findAll instead of filter -> Option D

4. Quick Check:

   Use findAll for filtering lists in Groovy [OK]

Hint: Use findAll, not filter, to filter lists in Groovy [OK]

Common Mistakes:

• Using filter instead of findAll causes syntax errors
• Thinking list must be a map for filtering
• Believing quotes type causes syntax error

5. You want a Jenkins job parameter that lists all Git branches dynamically from a repository URL. Which approach correctly implements this dynamic parameter?

hard

A. Use Active Choices Plugin with a Groovy script that runs git ls-remote --heads <repo_url> and parses branch names

B. Use a String parameter and ask users to type branch names manually

C. Use a Boolean parameter to select if branches should be listed

D. Use a fixed Choice parameter with hardcoded branch names

Solution

1. Step 1: Identify dynamic branch listing method

   Active Choices Plugin with Groovy script can run shell commands to fetch live branch names from Git.

2. Step 2: Exclude static or unrelated options

   String parameter requires manual input, Boolean parameter is not for listing, fixed Choice is static and not dynamic.

3. Final Answer:

   Use Active Choices Plugin with a Groovy script that runs git ls-remote --heads <repo_url> and parses branch names -> Option A

4. Quick Check:

   Active Choices + git command fetches dynamic branches [OK]

Hint: Use Active Choices with git command to list branches dynamically [OK]

Common Mistakes:

• Using static parameters instead of dynamic scripts
• Choosing Boolean parameter for listing options
• Forgetting to parse git command output