Note_Tech

All technological notes.

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Kubernetes Networking: Service - LoadBalancer

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• Kubernetes Networking: Service - LoadBalancer
  • LoadBalancer
  • Install MetalLB

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LoadBalancer

• LoadBalancer

  • a Kubernetes Service type that exposes application to the outside world using a cloud provider’s load balancer.
  • automatically provisions an external load balancer (e.g., AWS ELB, GCP LB, Azure LB) and links it to the Service.
    • External clients can reach the app using the LB’s public IP or DNS name.
  • Internally, it still uses ClusterIP + NodePort under the hood.

• How it works

• with AWS cloud

# nginx-loadbalancer.yaml
apiVersion: v1
kind: Service
metadata:
  name: nginx-loadbalancer
spec:
  type: LoadBalancer
  selector:
    app: nginx
  ports:
    - protocol: TCP
      port: 80 # Service port (LB port)
      targetPort: 80 # Pod port

1. Service Creation
   • cmd: kubectl apply -f nginx-loadbalancer.yaml
   • API server store Service into etcd
   • cloud-controller-manager call AWS API to create AWS ELB with
     • public IP address
     • DNS name
   • automatically create a NodePort on each node
   • automatically create a ClusterIP for nginx

• 1. Client request
     • Client (Internet) → AWS ELB (3.120.45.67:80) → NodeIP:31234 → ClusterIP (10.96.0.20:80) → Pod IP (10.244.x.x:80)
     • kube-proxy Handles Pod Selection
       • Traffic hitting NodePort 31234 is forwarded to Service ClusterIP 10.96.0.20.
       • ClusterIP is mapped to the Endpoints list (your Nginx Pods).
       • kube-proxy load balances traffic across Pods (whether local or on other Nodes).

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• LoadBalancer service type is an extension of the NodePort type,

  • load balancer stands in front of the nodes and handles the connections coming from the clients.
  • routes each connection to the service by forwarding it to the node port on one of the nodes.

• the client never attempts to connect to an unavailable node because the load balancer forwards traffic only to healthy nodes.

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Install MetalLB

• ref: https://metallb.io/

kubectl apply -f https://raw.githubusercontent.com/metallb/metallb/v0.15.3/config/manifests/metallb-frr.yaml