Declarative vs Imperative IaC: What’s the Difference?

The primary difference is that imperative IaC provides the precise, sequential orders to reach that state, whereas declarative IaC defines the intended final state of the infrastructure and lets the tool figure out how to achieve it. Because they abstract the “how,” declarative approaches are frequently simpler and easier to manage, while imperative approaches offer more granular control but necessitate your own management of the logic and order of commands.

Declarative IaC

• What it is: You describe the desired end state of your infrastructure—what you want it to look like—and the IaC tool handles the process of getting there.
• Example: You create a file that states, “I want a virtual machine with these properties.” The tool figures out the necessary commands to create or modify the VM to match your description.
• Key characteristics:
  • Focuses on the “what,” not the “how”.
  • Simpler syntax and files are often less complex to write and read.
  • More consistent and less error-prone because the tool manages the state and handles complex logic.
  • Tools often have built-in logic for idempotency (running the same configuration multiple times has the same result). 

Imperative IaC

• What it is: You provide a specific sequence of commands that must be executed in the correct order to achieve the desired outcome.
• Example: You write a script with commands like create-server, configure-firewall, and install-software that must be run in a particular sequence.
• Key characteristics:
  • Focuses on the “how”—the explicit steps to take.
  • More detailed and complex as you must manage every step, including error handling.
  • Can be more flexible for certain tasks that require precise, step-by-step control.
  • Can be more difficult to manage over time, especially for complex infrastructure, because you have to write the logic to handle all potential changes. 

Which one to choose?

• Most modern IaC tools, like Terraform and Azure Resource Manager, are declarative, as this approach generally leads to more robust and maintainable infrastructure code.
• Declarative is the preferred approach for managing the desired state of cloud resources, while imperative might be used for specific, task-oriented automation within a broader declarative strategy. 

A DevOps technique called Infrastructure as Code, or IaC, entails converting your infrastructure specifications into software scripts. This saves time and reduces setup errors by enabling you to automatically provision and patch new resources. Configuration scripts are executed by IaC tools using either an imperative or declarative programming language. Before comparing declarative and imperative programming for DevOps infrastructure as code, let’s describe these two programming paradigms so you can see the benefits and drawbacks of each.

Declarative

In declarative programming, the IaC tool determines how to accomplish the desired outcome on its own once you describe the name and characteristics of the infrastructure resources you want to provision. You tell your IaC tool what you want, but you don’t tell it how to get there. Terraform, Puppet, Ansible, Salt, and CloudFormation are a few well-known IaC tools that employ the declarative programming model.

Pros and Cons

One prominent method for writing infrastructure as code is declarative programming. The IaC solution determines how to reach the final configuration’s intended end-state once you specify it. Because declarative programming is extremely idempotent, or repeatable, you can repeatedly run your IaC instructions and still get the same outcome. Because the provisioning stages of the IaC tool are not explicitly stated, the declarative paradigm also responds well to configuration drift, which is the unavoidable, gradual modifications to your infrastructure over time.

Read Also: The Evolution of Infrastructure Management: From Manual to Code

Giving up a lot of control over each phase of the provisioning process is the declarative approach’s main disadvantage. Declarative programming can overcomplicate things and slow down the process, therefore it’s not the ideal option for minor updates and adjustments that can be handled by a straightforward CLI (command line interface) script.

Imperative 

In imperative programming, you give the IaC tool a set of instructions on how to provision a new resource. Using a series of command imperatives, you instruct your IaC tool on how to construct each environment. Ansible and Salt both enable imperative programming to some extent, and Chef is a well-known imperative IaC tool.

Pros and Cons

However, because you have to create instructions for each provisioning step, imperative programming necessitates a deeper understanding of scripting. When you need to make minor adjustments, optimize for a particular goal, or take software idiosyncrasies into consideration, this gives you flexibility over how you complete infrastructure chores.

The imperative approach’s primary drawback is that it necessitates a high degree of programming language proficiency, which infrastructure teams may not currently possess in the early phases of the DevOps journey. Imperative IaC scripts are frequently less idempotent as well; depending on the environment, your predetermined procedures may produce different outcomes. Furthermore, imperative IaC scripts are so detailed that a single mistake could lead to the failure of the entire process.

Understanding the difference between declarative and imperative approaches can help you effectively manage your infrastructure:

• Simplicity: Declarative tools are often easier to work with because you focus on “what” you want, rather than “how” to do it. This can save time and reduce errors.
• Control: Imperative tools may provide more control over the specific actions taken. This can be useful in complex environments where fine-tuning is necessary.

• Use Declarative: If you want to define the final state of your infrastructure without getting bogged down in details. This is common in cloud services where you want to create and manage large environments quickly.
• Use Imperative: When you need a step-by-step process for very specific configurations or tasks. This might be useful in automation scripts where exact control is essential.

In general, the declarative approach is preferred by many enterprises looking to fully automate and orchestrate their DevOps infrastructure. Without years of coding knowledge, you may write highly repeatable and flexible configuration scripts using declarative IaC tools. However, the imperative method is frequently more straightforward and easier to handle if you’re just starting off with a few CLI scripts or if you don’t require a whole orchestration platform.

There are advantages and disadvantages to both declarative and imperative IaC. The effectiveness and dependability of your infrastructure management can be greatly impacted by your choice. Keep in mind that the ideal tool is the one that meets your requirements and enables you to deliver software more quickly and consistently.