N+K: High Availability Solution for Stateful Service

"1 active + 1 standby" model is often used to provide high availability for stateful service handling. However, this model is not very efficiency and it is not cloud native as more and more services are migrating to cloud. This article introduces another "N+K" model to achieve same purpose, which is more cost efficient and cloud native. This article describes the principle and implementation of "N+K" model, and discusses its advantages and challenges comparing with "1+1" model.