what-if runs before every template deployment — no exceptions on prod.

Why this rule exists

what-if is a free preview of adds, changes, and deletes. Reading thirty seconds of output has caught entire categories of "the template also deleted X" incidents.

In practice

az deployment group what-if with the exact parameters of the real run, in the pipeline, with the output attached to the change record. A surprising delete in the preview stops the deploy.

Sources

• Microsoft Learn — ARM template deployment what-if — The preview operation itself