How to implement application updates in Kubernetes with minimal downtime using StatefulSet?

To update applications in Kubernetes with minimal downtime when using StatefulSet, the Rolling Update strategy with ordered pod updates is typically employed. StatefulSet updates pods one by one, starting from the highest index, which allows maintaining order and state.

Main steps:

1. Update the container image in the StatefulSet manifest.
2. Ensure that the updateStrategy parameter is set to RollingUpdate (default).
3. Kubernetes will sequentially terminate and restart pods with the new image, starting from the last.

This ensures that at any given time, the majority of pods are running, minimizing downtime.

Configuration example:

updateStrategy:
  type: RollingUpdate

For more granular control, preStop hooks or readinessProbe can be used to prevent pods from accepting traffic until they are fully ready.