In Kubernetes (K8S), achieving high availability for the API Server (kube-apiserver) is a key part of building a stable and reliable cluster architecture. The following are the main ways to achieve high availability for Kubernetes API Server:
1. Redundant deployment:
- Multiple API Server instances are typically deployed and are stateless between them so that in the event of a crash or maintenance of any one instance, the other instances can continue to process requests.
- These instances can run on different physical or virtual nodes to reduce the risk of a single point of failure.
2. load balancing:
- Configure a load balancer (e.g., cloud service provider's load balancer, Nginx, HAProxy, etc.) on the front-end to distribute client requests evenly to all API Server instances.
- For communication between internal components, you can use internal service discovery mechanisms and load balancing strategies, such as kube-proxy.
3. shared storage:
- All API Server instances need to access the same etcd cluster, and etcd itself needs to be made highly available. etcd serves as the data storage center for Kubernetes, storing all cluster state information to ensure consistency and persistence of API Server reads and writes.
4. health check and automatic recovery:
- Each API Server instance can be health-checked by the built-in Liveness Probe and Readiness Probe. kubelet or container orchestration system will automatically restart unhealthy instances when detection fails.
- The configuration monitoring system continuously monitors the health of the API Server and triggers the recovery mechanism when necessary.
5. synchronization time:
- All API Server instances and related control plane components should keep time synchronized to prevent certificate validation errors and other synchronization problems caused by time desynchronization.
6. security configuration:
- Use reasonable network isolation policies to ensure that communication between API Servers is secure, as well as between clients and API Servers via encrypted connections.
7. certificate management:
- Ensure that each API Server instance has its own service certificate and is properly trusted in the cluster to be able to process encrypted requests.
To summarize, Kubernetes API Server can provide highly available services and ensure the continuity and stability of the cluster's external services even in the event of failure or maintenance.