Service Type in k8s

Briefing

1 𝐂𝐥𝐮𝐬𝐭𝐞𝐫𝐈𝐏 (𝐃𝐞𝐟𝐚𝐮𝐥𝐭)

• Exposes the Service internally within the cluster.
• Pods in the same cluster can access the Service using its ClusterIP address or DNS name. Common use case: Microservices communicating with each other.

2 𝐍𝐨𝐝𝐞𝐏𝐨𝐫𝐭

• Exposes the Service externally by binding a port to each Node in the cluster.
• Accessible using <NodeIP>:<NodePort>. Common use case: Direct access for debugging or development.

3 𝐋𝐨𝐚𝐝𝐁𝐚𝐥𝐚𝐧𝐜𝐞𝐫

• Creates a cloud provider’s external load balancer (e.g., AWS ELB, Google Cloud Load Balancer).
• Exposes the Service to the internet with a public IP address. Common use case: Production applications requiring public access

4 𝐄𝐱𝐭𝐞𝐫𝐧𝐚𝐥𝐍𝐚𝐦𝐞

• Maps the Service to an external DNS name.
• Does not create a proxy but resolves the DNS name directly. Common use case: Accessing external services or legacy systems.

5 𝐇𝐞𝐚𝐝𝐥𝐞𝐬𝐬 𝐒𝐞𝐫𝐯𝐢𝐜𝐞

• A Headless Service is a specialized type of Kubernetes Service that does not assign a ClusterIP.
• Instead of routing traffic through a proxy (like kube-proxy), it directly returns the IP addresses of the Pods backing the Service. Common use case: Used with StatefulSets to ensure each Pod gets its own DNS entry.

Service Type ClusterIP

• ClusterIP is the default service type
• the service is assigned an IP from a designated service CIDR range
• DNS pattern: <namespace_name>.svc.cluster.local.

e.g.

apiVersion: v1
kind: Service
metadata:
  name: web1-svc
spec:
  selector:
    app: web1
  ports:
  - port: 80
    targetPort: 8080

Service Type NodePort

Service Type ExternalName

e.g.

kind: Service
apiVersion: v1
metadata:
  name: prod-mongodb
  namespace: prod
spec:
  type: ExternalName
  externalName: mymongodb.documents.azure.com

Service Type LoadBalancer

e.g.

kind: Service
apiVersion: v1
metadata:
  name: web-svc
spec:
  type: LoadBalancer
  selector:
    app: web
  ports:
  - protocol: TCP
    port: 80
    targetPort: 8081
  loadBalancerIP: 13.12.21.31
  loadBalancerSourceRanges:
  - "142.43.0.0/16"

Ingress and Ingress Controllers

The Ingress API is basically an HTTP-level router that allows for host-based and path-based rules to direct to specific backend services.

Reference

• Kubernetes Best Practices, Brendan Burns

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