Cascade Regional Airlines wants to swap a staging slot into production for the booking site, but the team wants a chance to run smoke tests against production settings and connection strings applied to the staging slot before traffic actually switches over, with the ability to cancel if something looks wrong. Which App Service feature supports this?

Swap with preview, also called a multi-phase swap, lets the team apply the target slot's settings — such as production connection strings and app settings — to the source (staging) slot without yet routing live traffic to it, so smoke tests can run against a slot that is configured exactly like production while it is still isolated. If the tests pass, the swap is completed and traffic switches over; if something looks wrong, the swap can be canceled and the staging slot reverts to its prior configuration, avoiding any impact to live users. Auto-swap does the opposite of what's wanted here: it completes the entire swap automatically and immediately after a deployment, with no opportunity to test production settings first or to cancel. Traffic routing percentages let a portion of production traffic be diverted to a slot for canary-style testing with real users, but that still exposes live traffic to the slot rather than giving an isolated pre-swap testing window. Temporarily pointing a custom domain at the staging slot changes reachability for manual browsing but does not apply production app settings or provide a controlled, cancelable swap workflow. As an operational check, after completing the preview phase, verify the phase-two completion or cancellation was actually applied by checking the slot's swap history in the portal.