AKS 20 – Explain Service manifest file

apiVersion: v1

• What it does: Specifies the API version for the Service object.
• Why it’s used: v1 is the stable version for core Kubernetes resources like Services, Pods, and ConfigMaps.

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🔹 kind: Service

• What it does: Declares the type of Kubernetes object.
• Why it’s used: A Service provides a stable network endpoint to access one or more Pods.

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🔹 metadata:

• What it does: Provides metadata about the Service.

Why it’s used: This is the name of the Service, used to reference it within the cluster.

spec:

• What it does: Defines the desired behavior of the Service.

selector:

    app: welcome-app

Why it’s used: This tells the Service to route traffic to Pods with the label app: welcome-app. It must match the labels defined in the Deployment.

ports:

• What it does: Defines how the Service exposes ports.

– protocol: TCP

    port: 80

    targetPort: 80

Why it’s used:

• protocol: TCP: Specifies the protocol used.
• port: 80: The port on which the Service is exposed inside the cluster.
• targetPort: 80: The port on the Pod that the traffic is forwarded to (must match the container’s exposed port).

type: ClusterIP

• What it does: Defines the type of Service.
• Why it’s used: ClusterIP exposes the Service on an internal IP within the cluster. It’s the default type and is used for internal communication between services (e.g., frontend calling backend).

✅ Summary

This Service:

• Routes traffic to Pods labeled app: welcome-app.
• Forwards requests from port 80 to port 80 on the container.
• Is only accessible within the cluster (not from outside).

Other services

1. ClusterIP (default)

• Access: Internal only (within the cluster).
• Use case: Microservices communicating with each other.
• Example: Backend service accessed by frontend pods.

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2. NodePort

• Access: Exposes the Service on a static port on each Node’s IP.
• Use case: Quick external access for testing or small-scale apps.
• How it works:
  • Kubernetes allocates a port (default range: 30000–32767).
  • You can access the service via NodeIP:NodePort.

type: NodePort

3. LoadBalancer

• Access: Exposes the Service externally using a cloud provider’s load balancer.
• Use case: Production apps needing external access.
• How it works: Automatically provisions an external IP and routes traffic to the Service.

type: LoadBalancer

Requires cloud provider support (e.g., Azure, AWS, GCP).

4. ExternalName

• Access: Maps the Service to an external DNS name.
• Use case: Accessing external services (e.g., a database or API outside the cluster).
• How it works: No proxying; just DNS redirection.

type: ExternalName

externalName: my.database.example.com

5. Headless Service (ClusterIP: None)

• Access: No cluster IP is assigned.
• Use case: StatefulSets, DNS-based service discovery.
• How it works: Returns individual pod IPs instead of a single virtual IP.

clusterIP: None