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Services

Goals​

  1. Understand Kubernetes Services:
    • Learn what a Service is and its role in the Kubernetes architecture.
  2. Basic Example(s):
    • Provide (a) basic example(s) of Services.
    • Show how to define a Service using YAML.
  3. Service Spec Explanation:
    • Explain the components of the Service specification using the example(s) above.
  4. Service Types:
    • Describe different types of Services and their use cases (ClusterIP, NodePort, LoadBalancer, ExternalName).
  5. Exercise:
    • Hands-on activity to create a simple Service.

Understanding Kubernetes Services​

A Service in Kubernetes is an abstraction that defines a logical set of pods and a policy by which to access them. Services enable networking and connectivity between different parts of a Kubernetes application or with external services.

Basic Service Example​

1. ClusterIP Service​

Here is a basic example of a Kubernetes Service specification in YAML:

apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
  type: ClusterIP

This Service provides a stable IP and DNS name to access the set of nginx pods.

Save this to a file service.yaml and create the resource using kubectl apply -f service.yaml:

> kubectl apply -f service.yaml
service/nginx-service created

NodePort Service​

First we create the server Pod service-simple-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: nginx
spec:
  containers:
  - name: nginx-container
    image: nginx:latest
    ports:
    - containerPort: 80

We then create the corresponding service for the pod service-simple.yaml

apiVersion: v1
kind: Service
metadata:
  name: nginx-nodeport
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
    nodePort: 30001
  type: NodePort

We proceed to create both:

> kubectl apply -f service-simple-pod.yaml 
> kubectl apply -f service-simple.yaml

We then find the Node's IP:

> minikube ip

And then we try to curl from the terminal:

> curl http://$(minikube ip):30001
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Service Spec Explanation​

  1. apiVersion: v1 (hardcoded)
  2. kind: Service (type of the resource)
  3. metadata: ObjectMeta
  4. spec: ServiceSpec
  5. status: ServiceStatus

Service Types​

  • ClusterIP: Exposes the Service on a cluster-internal IP. This is the default type.
  • NodePort: Exposes the Service on each Node's IP at a static port. (We'll be using this for examples)
  • LoadBalancer: Exposes the Service externally using a cloud provider's load balancer.
  • ExternalName: Maps a Service to an external DNS name.

Exercises​

Exercise 1: Expose an Application Internally Using a ClusterIP Service​

Objective: Deploy an application and expose it within the cluster using a ClusterIP Service.

Task:

  • Deploy a pod running a simple HTTP server (e.g., nginx or httpd).
  • Create a ClusterIP Service to expose this HTTP server within the Kubernetes cluster.
  • Verify that the service is accessible from other pods in the cluster.
tip

You can deploy a Pod running a simple linux image (ubuntu:22.04). Shelling into it was shown previously on the Pods page, do you remember how to do it without looking at it?