How can Terraform variables be provided to a configuration?

• A. They are only defined in the variables file
• B. They must be hard-coded in the configuration
• C. They cannot be overridden at apply time
• D. They can be provided via environment variables, -var command-line flag, or .tfvars files

Answer: (D)

Terraform variables can be provided from multiple sources and overridden at plan or apply time. You can supply values through environment variables (using the TF_VAR_ prefix), via the -var CLI flag to set a specific value, or with .tfvars files that Terraform reads to fill in variable values. This mix gives you flexibility to keep configuration separate from data and to adapt configurations for different environments without editing the code. Therefore, the method described—environment variables, the -var flag, or .tfvars files—covers the standard ways to provide variable values. The other statements are not accurate because variables aren’t limited to a single file, don’t have to be hard-coded, and can indeed be overridden at apply time through these mechanisms.