How to achieve horizontal scaling in Kubernetes?

Kubernetes (K8s) is an open-source container orchestration and management platform that makes it easy to achieve horizontal scaling. Here are some methods to achieve horizontal scaling.

1. Utilizing ReplicaSets: In Kubernetes, horizontal scaling can be achieved by creating ReplicaSets. A ReplicaSet is a collection of Pods with identical configurations, where the desired number of Pods can be specified and Kubernetes will automatically create or delete Pods to maintain the specified number of replicas. When scaling horizontally is needed, simply updating the replica count in the ReplicaSet is all that’s required.
2. Utilizing Horizontal Pod Autoscaler (HPA): HPA is a mechanism provided by Kubernetes for automated scaling in and out. By configuring the HPA, the number of replicas can be automatically adjusted based on metrics such as CPU and memory usage of the Pods. When the workload increases, the HPA will automatically increase the number of replicas, and when the workload decreases, it will automatically decrease the number of replicas.
3. Deployment is a high-level abstraction in Kubernetes that defines Pods and ReplicaSets. By creating a Deployment object, you can easily manage the lifecycle of Pods and ReplicaSets and also support features such as rolling updates and rollbacks. When horizontal scaling is needed, simply update the replica number of the Deployment.
4. Utilize custom metrics: In addition to the built-in metrics like CPU and memory utilization, Kubernetes also supports the use of custom metrics for horizontal scaling. You can collect and report custom metrics using monitoring systems like Prometheus, and configure the horizontal autoscaler to scale in or out based on these metrics.

When implementing horizontal scaling, it is important to consider the scalability and state sharing of the application. A better horizontal scaling effect can be achieved by designing the application as stateless, horizontally scalable microservices.