Pros and Cons of Declarative vs Scripted Pipelines

Jenkins pipelines allow you to define and automate your Continuous Integration (CI) and Continuous Delivery (CD) processes. Jenkins provides two types of pipeline syntax—Declarative and Scripted. While both offer powerful ways to define your pipeline, they have different use cases, strengths, and weaknesses. In this post, we will explore the pros and cons of each pipeline style to help you make an informed decision when building your CI/CD workflows.

1. Overview of Jenkins Pipelines

Before diving into the pros and cons of Declarative and Scripted pipelines, let's briefly discuss what Jenkins pipelines are.

A Jenkins pipeline defines your automation process, typically for building, testing, and deploying software applications. Pipelines consist of stages, steps, and agents that dictate the various tasks to be executed, as well as the environment in which they are run.

Jenkins offers two types of pipelines:

• Declarative Pipelines: A newer, simplified pipeline syntax with a predefined structure.
• Scripted Pipelines: A more flexible pipeline syntax based on Groovy scripting language.

Understanding the strengths and limitations of both pipeline types is critical for optimizing your CI/CD workflows.

For even more about about Jenkins Pipelines, check my previuos post Basic Jenkinsfile Syntax for Both Declarative and Scripted Pipelines.

2. What is a Declarative Pipeline?

Declarative pipelines were introduced in Jenkins 2.x as a way to simplify and standardize pipeline creation. They are designed to provide a more structured, readable, and user-friendly way to define pipelines. In a Declarative pipeline, the pipeline syntax is predefined, and it enforces a clear, logical separation of stages and steps.

Declarative pipelines always start with the pipeline {} block, and you can define stages, agents, and post-build actions inside this block.

Here is a simple example:

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                echo 'Building...'
            }
        }
        stage('Test') {
            steps {
                echo 'Testing...'
            }
        }
        stage('Deploy') {
            steps {
                echo 'Deploying...'
            }
        }
    }
}

3. What is a Scripted Pipeline?

Scripted pipelines are the original pipeline type, based on Groovy scripting. They provide full flexibility and control over the pipeline process. Because they are more freeform, they can be used to build highly customized and complex pipelines.

Unlike Declarative pipelines, Scripted pipelines use the node {} block to define where the pipeline will run. Here’s a simple Scripted pipeline example:

node {
    stage('Build') {
        echo 'Building...'
    }
    stage('Test') {
        echo 'Testing...'
    }
    stage('Deploy') {
        echo 'Deploying...'
    }
}

Scripted pipelines allow you to write Groovy code for advanced logic and complex behavior.

4. Pros and Cons of Declarative Pipelines

4.1 Pros of Declarative Pipelines

1. Simplicity and Readability:

• Declarative pipelines have a straightforward, predefined structure that is easy to read and understand. This makes them ideal for users who are new to Jenkins or for teams that require clear and concise pipeline definitions.

2. Error Handling and Validation:

• Declarative pipelines come with built-in error handling and syntax validation. Jenkins can detect and flag errors in your pipeline configuration before the pipeline starts, reducing the risk of runtime issues.

3. Best Practices Encouraged:

• The structured format of Declarative pipelines naturally encourages the use of best practices in pipeline development. For example, using stages and post-build actions is more intuitive in Declarative pipelines.

4. Cleaner Code:

• Declarative pipelines keep pipeline code clean and organized, as it enforces a strict structure for stages, agents, steps, and post actions. This is especially useful for larger teams or projects where readability and maintainability are key.

5. Reduced Learning Curve:

• The predefined structure of Declarative pipelines means that you don’t need to learn Groovy to write simple pipelines. This reduces the learning curve for developers who are not familiar with Groovy scripting.

6. Integration with Blue Ocean:

• Declarative pipelines are better integrated with Jenkins’ Blue Ocean interface, making it easier to visualize and manage pipelines in a graphical UI.

4.2 Cons of Declarative Pipelines

1. Limited Flexibility:

• While Declarative pipelines are great for standard workflows, they can be too restrictive for more complex use cases. The rigid structure may not allow for advanced customization or dynamic behavior that is easily achievable in Scripted pipelines.

2. Difficulty in Handling Complex Logic:

• For pipelines that require loops, conditionals, or advanced logic, Declarative pipelines can be limiting. While some logic is supported (such as when conditions), it is far more cumbersome compared to Scripted pipelines.

3. Not Suitable for Advanced Users:

• Developers and teams who require full control over the pipeline or need to implement complex workflows may find Declarative pipelines too constrained. Advanced Groovy features cannot be fully utilized in this structure.

5. Pros and Cons of Scripted Pipelines

5.1 Pros of Scripted Pipelines

1. Maximum Flexibility:

• Scripted pipelines provide complete control over the build process, as they are written using Groovy. You can implement any custom logic you need, such as loops, conditionals, error handling, and even dynamically generating stages.

2. Groovy Language Support:

• Since Scripted pipelines are essentially Groovy scripts, you can leverage the full power of Groovy within your pipeline. This opens up possibilities for highly customized and dynamic pipelines.

3. Ideal for Complex Pipelines:

• Scripted pipelines shine when you need to create complex pipelines with non-linear execution paths, complex conditionals, or dynamic behavior. They allow for sophisticated workflows that would be hard to replicate in a Declarative pipeline.

4. No Structural Constraints:

• Scripted pipelines don’t have the rigid structure of Declarative pipelines, giving developers the freedom to organize their pipelines as they see fit. This is useful for experienced users who prefer more granular control.

5. Backwards Compatibility:

• Scripted pipelines have been around longer than Declarative pipelines and are fully backwards compatible with older versions of Jenkins. This makes them a good choice if you have legacy pipelines or plugins that depend on Scripted syntax.

5.2 Cons of Scripted Pipelines

1. Steeper Learning Curve:
   • Scripted pipelines require a solid understanding of Groovy. For developers unfamiliar with Groovy or pipeline syntax, the learning curve can be steep, especially compared to Declarative pipelines.
2. Less Readable and Maintainable:
   • Due to the lack of predefined structure, Scripted pipelines can become difficult to read and maintain, especially for large teams. The flexibility offered can lead to inconsistent code styles and poorly organized pipelines.
3. Harder to Debug:
   • Without the built-in validation and error handling of Declarative pipelines, Scripted pipelines can be prone to runtime errors that are harder to debug. Syntax errors or logic mistakes might not be caught until the pipeline is running.
4. Longer Development Time:
   • Writing a Scripted pipeline from scratch often requires more time and effort compared to a Declarative pipeline. The extra complexity and custom Groovy code can slow down development, particularly for simpler workflows.
5. Less Visual Tooling:
   • Scripted pipelines are less integrated with the Blue Ocean interface, making it harder to visualize or manage pipelines in a graphical UI. This could be a drawback for teams that prefer a more user-friendly interface.

6. Declarative vs Scripted: Which One to Choose?

When to Choose Declarative Pipelines:

• Beginner-Friendly: If you're new to Jenkins or pipelines in general, start with Declarative pipelines. Their structured, readable syntax makes it easier to learn and manage pipelines.
• Simple or Standard Workflows: Declarative pipelines are best suited for straightforward CI/CD workflows that don’t require complex logic or customization.
• Team Collaboration: Declarative pipelines are ideal for large teams where pipeline readability, maintainability, and adherence to best practices are important.
• Consistent and Predictable: If you want

to enforce a consistent pipeline structure across your organization, Declarative pipelines are the way to go.

When to Choose Scripted Pipelines:

• Advanced Users: If you’re comfortable with Groovy scripting and need maximum flexibility, Scripted pipelines provide the tools you need.
• Complex Pipelines: For pipelines that require dynamic stage generation, advanced error handling, or intricate logic, Scripted pipelines offer more control.
• Legacy Support: If you have existing Scripted pipelines or need backwards compatibility with older Jenkins versions or plugins, sticking with Scripted pipelines may be the better choice.

Conclusion

Both Declarative and Scripted pipelines have their strengths and weaknesses, and the choice between them depends on the specific needs of your project. Declarative pipelines offer a more structured, user-friendly approach that simplifies pipeline development and enforces best practices. On the other hand, Scripted pipelines provide greater flexibility and power for complex use cases but come with a steeper learning curve.

In many cases, a combination of both pipeline types might be the best approach. You can start with Declarative pipelines for simplicity and then transition to Scripted pipelines as your CI/CD processes grow more complex.

Ultimately, choosing the right pipeline type will help you optimize your Jenkins workflows, improve team productivity, and achieve more reliable automation in your software development lifecycle.