When deploying a new version of an application in GKE, which Deployment strategy ensures at least one replica is always available?

The Deployment strategy that guarantees at least one replica is always available during the rollout of a new version in Google Kubernetes Engine (GKE) is the RollingUpdate strategy with maxSurge set to 1 and maxUnavailable set to 0.

In this configuration, maxSurge allows one additional pod to be created during the update process beyond the desired number of replicas, which provides extra capacity. At the same time, maxUnavailable is set to 0, ensuring that no existing pods are taken down during the update. This combination allows for seamless updates as at least one replica remains available throughout the deployment process. Hence, the application maintains its availability without any downtime.

In contrast, the other options either introduce scenarios where existing replicas could be taken down during the update (leading to potential downtime) or limit the rollout capacity, which does not ensure continuous availability.