Declarative vs. Imperative Approaches

There are 2 approaches to the templates used when writing IaC configuration files. Different tools use different approaches, which are listed in the next section.

Declarative — you define the desired state of the final solution.

The tool or automation platform determines how the goal is reached, the step-by-step executions are handled by the tool and hidden from the user. Declarative tools are the most popular and most dominant in the IaC space. They are most useful when changes or updates need to be made to your solution.

Declarative tools are idempotent because you are defining the required state of the solution. Idempotency refers to a process that can be executed multiple times with the same result.

Imperative — you define the steps to execute in order to reach the desired solution.

An imperative approach allows you to build up multiple layers of commands to reach the end goal. Imperative tools give you more control over how the goal is reached. These tools are most useful when you need to deploy and not update or change the solution in the future.

Imperative approaches may not lead to idempotency, the end goal may be different depending on the starting point, as a series of steps form the process. Consider a process with 10 steps, for example, starting from step 1 would lead to a different result compared to starting with step 6.