Three common patterns for zero-downtime deployments

Rolling deploy — You progressively take old instances (version N) out of service while you bring up new instances (version N+1), ensuring that you maintain a minimum percentage of capacity during deployment.
Canaries — You add a single new instance into service to test the reliability of version N+1 before continuing with a full rollout. This pattern provides an added measure of safety beyond a normal rolling deploy.
Blue-green deploys — You create a parallel group of services (the green set), running the new version of the code; you progressively shift requests away from the old version (the blue set). This can work better than canaries in scenarios where service consumers are highly sensitive to error rates and can’t accept the risk of an unhealthy canary.