To build a High Availability (HA) Kubernetes cluster, you need to ensure that your cluster can withstand failures and continue to operate without significant downtime. Here are the key steps and considerations for setting up an HA Kubernetes cluster:
1. Control Plane Redundancy
Stacked Control Plane Nodes
Description: In this topology, the etcd nodes are co-located with the control plane nodes.
Setup: Each control plane node runs an instance of the kube-apiserver, kube-scheduler, and kube-controller-manager. The etcd members are also on these nodes.
Advantages: Simpler to set up and manage.
Disadvantages: If a node fails, both an etcd member and a control plane instance are lost, compromising redundancy.
Recommendation: Run a minimum of three control plane nodes to ensure redundancy[17].
External etcd Nodes
Description: The etcd nodes are separate from the control plane nodes.
Setup: Each control plane node runs the same components as in the stacked topology, but the etcd members are on separate nodes.
Advantages: Decouples the control plane and etcd, reducing the impact of node failures.
Disadvantages: Requires more infrastructure (at least three control plane nodes and three etcd nodes).
Recommendation: This setup is more resilient but requires more resources[17].
2. Load Balancing
API Server Load Balancer: Deploy a load balancer in front of the API server instances to distribute traffic. This ensures that if one API server instance goes down, the load balancer can redirect traffic to the remaining healthy instances[10].
Example Configuration: In a cloud environment, use a TCP forwarding load balancer that checks the health of the API servers on port 6443[10].
3. Replication and Autoscaling
Replication: Use replication controllers or deployments to ensure that multiple replicas of your pods are running. This helps in maintaining availability even if some pods fail[1][2].
Pod Autoscaling: Implement Horizontal Pod Autoscaling (HPA) to automatically adjust the number of pod replicas based on CPU utilization or other metrics[1].
4. Multi-Zone/Region Deployment
Cluster-Level Fault Tolerance: Deploy your Kubernetes cluster across multiple availability zones or regions to provide redundancy at the cluster level. This setup helps your application withstand failures or disruptions in a specific zone[1].
Managed Kubernetes Services: Many cloud providers offer managed Kubernetes services with built-in support for multi-zone or multi-region deployments[1].
5. Control Plane Components
API Server: Run multiple instances of the API server across different control plane nodes. Use a load balancer to ensure continuo...
