[Kubernetes] Service

source: Spectro Cloud

🌐 What is a Service in Kubernetes?

A Service is an abstraction that defines a stable way to access a set of Pods (usually grouped by a label selector). It exposes an application running in your cluster behind a single outward-facing endpoint, even when the workload is split across multiple backends.

 

Since Pods are ephemeral (they come and go), a Service ensures that your app always has a reliable network endpoint — even when Pods are recreated or rescheduled.

 

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app.kubernetes.io/name: MyApp
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376

---

🔍 Key Characteristics

Feature	Description
Stable IP and DNS	Services expose a constant virtual IP (ClusterIP) and DNS name.
Load Balancing	Distributes traffic across matching Pods.
Selector-based	Uses labels to find the target Pods.
Decouples Clients	Clients don't need to know Pod IPs — just talk to the Service.
Multiple Types	Different types let you expose services internally or externally.

---

📦 Service Types

source : Medium

1. ClusterIP (default)

• Internal-only access.
• Exposes service on a cluster-internal IP.
• Cannot be accessed from outside the cluster.

➡️ Example: Frontend app talking to a backend service.

apiVersion: v1
kind: Service
metadata:
  name: my-backend-service
spec:
  type: ClusterIP # Optional field (default)
  clusterIP: 10.10.0.1 # within service cluster ip range
  ports:
  - name: http
    protocol: TCP
    port: 80
    targetPort: 8080

 

---

source : Medium

2. NodePort

• Exposes the service on each Node’s IP at a static port.
• Can be accessed externally using NodeIP:NodePort.

source : StackOverflow

➡️ Example: Testing service externally on a fixed port.

apiVersion: v1
kind: Service
metadata:
  name: my-frontend-service
spec:
  type: NodePort
  selector:
    app: web
  ports:
  - name: http
    protocol: TCP
    port: 80
    targetPort: 8080
    nodePort: 30000 # 30000-32767, Optional field

---

source : Medium

3. LoadBalancer

• Integrates with cloud providers to create an external load balancer.
• Exposes service to the internet with an external IP.

➡️ Example: When you are using a cloud provider to host your Kubernetes cluster.

apiVersion: v1
kind: Service
metadata:
  name: my-frontend-service
spec:
  type: LoadBalancer
  clusterIP: 10.0.171.123
  loadBalancerIP: 123.123.123.123
  selector:
    app: web
  ports:
  - name: http
    protocol: TCP
    port: 80
    targetPort: 8080

---

source : Medium

4. ExternalName

• Maps a service to an external DNS name instead of routing to Pods.
• No selector or pods involved.

➡️ Example: Accessing an external database via a local service name.

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  type: ExternalName
  externalName: my.database.example.com

---

🧠 Bonus: Headless Service

• Set clusterIP: None
• Directly returns Pod IPs instead of a proxy IP.
• Used with StatefulSets or for service discovery.

---

References

 - Service | Kubernetes

 - Kubernetes — Service Types Overview | by Ashish Patel | DevOps Mojo | Medium

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