Kubernetes Networking: Understanding the Role of Services

Question: “Is a Kubernetes Service just a load balancer?”

Not exactly. A Kubernetes Service does much more than load balancing.
It provides a stable and consistent network endpoint for Pods, even when their IP addresses change, and works with kube-proxy and DNS to manage traffic routing and discovery.

In this post, we’ll cover:

• The primary role and functions of a Kubernetes Service
• How kube-proxy and Endpoints work behind the scenes
• Service and DNS integration
• A detailed look at how Service traffic flows

1. The Core Role of a Service

A Service provides:

• A stable entry point despite changing Pod IPs.
• Load balancing across multiple Pods that match a label selector.
• Service discovery within the cluster.
• Integration with network policies to manage traffic security.

2. What Is the Role of kube-proxy?

kube-proxy is the component that routes traffic from a Service to the appropriate Pod(s).

• Automatically configures iptables or IPVS rules.
• Supports Service types like ClusterIP and NodePort.
• Uses load balancing methods such as round-robin.

3. How Services Use Endpoints

When a Service is created, Kubernetes matches Pods via the selector and stores their IP and port information in an Endpoints object.

Check Endpoints with:

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kubectl get endpoints

Example:

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NAME         ENDPOINTS          AGE
my-service   10.244.1.5:8080    1m

4. Service and DNS Integration

Kubernetes integrates Services with CoreDNS for automatic DNS resolution.

• Example DNS: my-service.default.svc.cluster.local
• ClusterIP Services are reachable within the cluster using these names.
• Best practice: Use Service names instead of Pod IPs for communication.

5. Service Traffic Flow

1. Service creation via YAML or kubectl expose.
2. Pod selection based on label selectors.
3. Endpoints object is generated with Pod IPs.
4. kube-proxy configures routing rules.
5. CoreDNS registers a DNS name for the Service.

6. Hands-On: Checking Services and Endpoints

Create a Service:

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kubectl expose deployment my-app --port=80 --target-port=8080 --type=ClusterIP

Check Endpoints:

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kubectl get endpoints my-app

7. FAQ (Answer Engine Optimization)

Q1. Can Pods communicate without a Service? A. Yes, via Pod IP, but since IPs change, Services are necessary for stable communication.

Q2. What happens if kube-proxy is disabled? A. Service traffic routing will fail, breaking connectivity.

Q3. Do I need DNS to access a Service? A. No, you can use the ClusterIP directly, but DNS names make it easier and more reliable.

8. Key Takeaways

9. Final Thoughts

Kubernetes Services are more than just load balancers; they are the foundation of stable networking and service discovery.