Canary releasing and blue-green deployment both reduce deployment risk, but they differ in how gradually the new version is exposed to users.
Key Points: • Canary releasing sends a small percentage of traffic to the new version first, monitors it, and gradually increases traffic if it behaves well. • Blue-green deployment keeps two full, identical environments and switches all traffic from the old to the new one in a single cutover after testing. • Canary gives real production feedback on a limited blast radius before a full rollout, which blue-green does not, since blue-green tests happen before the switch. • Blue-green's rollback is a simple traffic switch back to the old environment; canary rollback is just routing traffic away from the canary instances. • Canary requires more sophisticated traffic-splitting infrastructure, such as a service mesh or an advanced load balancer, than blue-green typically needs.
Example: For a checkout service change, a canary release might send 2% of live traffic to the new version for an hour and watch error rates before ramping up, while a blue-green deployment would instead fully test the new version in an idle "green" environment and then switch 100% of traffic over at once.
Interview Tip: A concise interview answer is:
"Canary releasing gradually shifts a small, increasing slice of real traffic to the new version so you get production feedback with a limited blast radius. Blue-green instead tests fully in an idle environment and then cuts all traffic over at once. Canary needs more traffic-splitting capability, but catches issues earlier with less user impact."