locking

Sessions, locks and pub/sub are three very different contracts with the same server. Knowing which guarantees each one lacks is the difference between a cache and an outage.

Everyone can say state maps config to reality. The follow-up that separates candidates is what else is in the file, and what that means for who may read it.

Everyone answers state locking. The follow-up is what happens when locking is not configured, and what you do with a stale lock at 2am, which is where the answer gets real.

Most migrations are safe and a handful can take the site down by holding a lock for eight seconds. Build the tooling to tell those apart automatically, because a review culture cannot do it two hundred times a month.