Your Cloud Run gRPC risk-calculation API needs to roll out optimizations to a subset of registered customers before full release. CI produced a new container image in Artifact Registry. Which rollout strategy should you use?

The correct answer is to use a feature flag. Feature flags allow you to selectively enable new functionality for specific users or groups (in this case, registered customers) without deploying a separate service or version. This provides fine-grained control over who experiences the new optimizations, which is ideal for a targeted rollout to a subset of users. Cloud Run traffic splitting routes a percentage of all traffic to a new revision, not specific users. Blue/green deployment involves switching all traffic from an old version to a new one, which doesn't allow for a subset rollout. Migrating traffic with session affinity also applies to all users and is more about maintaining user sessions than targeted feature release.