A common programming practice is refactoring, in which you restructure the internal details of an existing piece of code without changing its external behavior. The goal is to improve the readability, maintainability, and general hygiene of the code. Refactoring is an essential coding practice that you should do regularly. However, when it comes to Terraform, or any IaC tool, you have to be careful about what defines the “external behavior” of a piece of code, or you will run into unexpected problems.

For example, a common refactoring practice is to rename a variable or a function to give it a clearer name. Many IDEs even have built-in support for refactoring and can automatically rename the variable or function for you, across the entire codebase. Although such a renaming is something you might do without thinking twice in a general-purpose programming language, you need to be very careful about how you do it in Terraform, or it could lead to an outage.