How is load balancing implemented in Kubernetes…

Load balancing in Kubernetes is implemented at several levels:

Service (at the Kube-proxy level):
- Each Pod in a Service receives a unique IP address.
- Kube-proxy, running on each node, monitors changes in Service and EndpointSlice.
- Sets up traffic redirection rules (iptables, ipvs) to the cluster IP of the Service.
- Traffic arriving at the Service's cluster IP is distributed among the Pods of that Service according to the selected algorithm (default Round Robin).
- There are two modes of Kube-proxy operation: iptables (standard, based on Linux netfilter) and ipvs (more efficient for large clusters, based on Virtual Server API).
```
apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-app # Selects Pods with label app: my-app
  ports:
    - protocol: TCP
      port: 80 # Port on the Service
      targetPort: 8080 # Port on Pods
```

Ingress (at L7 level):

Acts as a single entry point for external HTTP/S traffic load balancing.
Requires an Ingress controller (e.g., Nginx Ingress Controller) to implement rules.
Routes traffic to a specific Service inside the cluster based on URL path, hostname, and other L7 rules.
Allows implementing various load balancing strategies, SSL termination, Name-based virtual hosting.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: my-ingress
spec:
  rules:
  - host: myapp.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: my-service # Routes traffic to this Service
            port:
              number: 80

LoadBalancer Service (cloud provider level):
- When creating a Service of type LoadBalancer, Kubernetes interacts with the cloud provider's API (AWS, GCP, Azure, etc.).
- The provider creates an external load balancer that directs traffic to the cluster nodes.
- Then Kube-proxy redirects traffic to Pods inside the cluster.
- This Service type provides external access and load balancing at L4 (TCP/UDP) or L7 (HTTP/S) depending on the provider.
```
apiVersion: v1
kind: Service
metadata:
  name: my-external-service
spec:
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
  type: LoadBalancer # Creates an external load balancer
```
Custom Load Balancers (e.g., HAProxy, Nginx as Pods):
- You can deploy a load balancer inside the cluster as a Deployment and Service (ClusterIP or NodePort).
- Configure external traffic to this Service.
- The load balancer will distribute traffic among other Pods independently.

Thus, Kubernetes offers a multi-layered approach to load balancing, combining built-in mechanisms (Service, Kube-proxy) with external solutions (Ingress, Cloud Provider Load Balancers) and the ability to deploy custom load balancers.

How is load balancing implemented in Kubernetes?