canary in the coal mine
expressionops culturesecurity
A sacrificial early-warning signal: something small that suffers first, so the rest can react in time.
Miners' literal canaries became the vocabulary of modern operations: canary deployments send a slice of traffic to the new version and watch it before the fleet follows; canary tokens are honeytoken credentials whose only job is to scream when touched.
Also known as: canary release, canary deployment