Zero-Downtime Deploys

Ship a new version without a maintenance window: rolling, blue-green, and canary deploys, plus the health checks and migrations that make them safe.

1. Why Naive Deploys Hurt The mental model: a deploy means two versions of your code want to exist at once, and stop-and-replace drops every request in that gap.
2. The Three Strategies Rolling, blue-green, and canary: how each moves live traffic from the old version to the new without a gap, and when to reach for which.
3. The Hard Part — Migrations and Health The database is what actually bites you: backward-compatible expand-then-contract migrations, plus health checks and connection draining that let the balancer route safely.