Canary vs Blue-Green

A canary release routes a small slice of traffic to the new version first, watches the signals, and widens gradually. It gathers real evidence at low blast radius and lets you abort after affecting only a few users. A blue-green deployment stands up a full second environment (green) alongside the current one (blue) and flips all traffic at once, with the old environment kept warm for instant rollback.

The axis that separates them is how you buy down reversal cost. Canary reduces exposure while learning — ideal when the change is risky and you want progressive evidence. Blue-green makes the switch itself instantly reversible — ideal when you cannot tolerate a mixed-version state (e.g., a schema-coupled change) but can validate the whole environment before the flip.

Neither eliminates the need for a parity eval before cutover: blue-green's clean flip is only safe if green has been proven equivalent to blue first. Canary spreads that validation across live traffic instead.