Start one pod at a time when replica is greater than one

Question

Is there a way to ensure that pods are scaled one at a time when setting replica greater than one?

Example: Replica set to 3

1. Pod 1 - Initializing , pod 2 - Waiting, pod 3 - Waiting
2. Pod 1 - Running , pod 2 - Initializing, pod 3 - Waiting
3. Pod 1 - Running , pod 2 - Running, pod 3 - Initializing
4. Pod 1 - Running , pod 2 - Running, pod 3 - Running

Answer 1

You can acomplish this behavior using StatefulSets. As it goes from Kubernetes docs

• For a StatefulSet with N replicas, when Pods are being deployed, they are created sequentially, in order from {0..N-1}.
• When Pods are being deleted, they are terminated in reverse order, from {N-1..0}.
• Before a scaling operation is applied to a Pod, all of its predecessors must be Running and Ready.
• Before a Pod is terminated, all of its successors must be completely shutdown.

So, as you can see here, new pod is not booted up until previous one is initializing.

Note: this behavior is guranteed by Kubernetes when OrderedReady pod management policy is used (which is default).