How does Terraform determine changes needed for the infrastructure?

Terraform determines changes needed for the infrastructure primarily by comparing the current state to the desired state defined in the configuration. This process involves checking the current state of the infrastructure, which Terraform manages in its state file, against the configuration files written in HashiCorp Configuration Language (HCL) or JSON that specify the desired end state.

When a Terraform plan is executed, it retrieves the current state from the state file and then looks at the configuration files to understand what the infrastructure should look like. If there are any discrepancies between the current state and the desired state, Terraform generates an execution plan that outlines the necessary actions to reach the desired state. These actions can include creating, modifying, or destroying resources as needed, ensuring that the infrastructure is provisioned in accordance with the specifications set forth in the configuration files.

This approach enables Terraform to manage infrastructure changes in a declarative manner, allowing infrastructure management to be consistent, predictable, and repeatable. By focusing on the desired state as defined in the configurations, Terraform can optimally make the required modifications to align the current infrastructure with what is specified, regardless of the order in which resources were created or modified.