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Provide Load-Balanced Access to an Application in a Cluster

This page shows how to create a Kubernetes Service object that provides load-balanced access to an application running in a cluster.

• Objectives
• Before you begin
• Creating a Service for an application running in two pods
• Using a service configuration file
• What’s next

Objectives

• Run two instances of a Hello World application
• Create a Service object
• Use the Service object to access the running application

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

• Katacoda
• Play with Kubernetes

Creating a Service for an application running in two pods

1. Run a Hello World application in your cluster:

    kubectl run hello-world --replicas=2 --labels="run=load-balancer-example" --image=gcr.io/google-samples/node-hello:1.0  --port=8080
   

2. List the pods that are running the Hello World application:

    kubectl get pods --selector="run=load-balancer-example"
   

   The output is similar to this:

    NAME                           READY     STATUS    RESTARTS   AGE
    hello-world-2189936611-8fyp0   1/1       Running   0          6m
    hello-world-2189936611-9isq8   1/1       Running   0          6m
   

3. List the replica set for the two Hello World pods:

    kubectl get replicasets --selector="run=load-balancer-example"
   

   The output is similar to this:

    NAME                     DESIRED   CURRENT   AGE
    hello-world-2189936611   2         2         12m
   

4. Create a Service object that exposes the replica set:

    kubectl expose rs <your-replica-set-name> --type="LoadBalancer" --name="example-service"
   

   where <your-replica-set-name> is the name of your replica set.

5. Display the IP addresses for your service:

    kubectl get services example-service
   

   The output shows the internal IP address and the external IP address of your service. If the external IP address shows as <pending>, repeat the command.

   Note: If you are using Minikube, you don’t get an external IP address. The external IP address remains in the pending state.

   NAME              CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
   example-service   10.0.0.160   <pending>     8080/TCP   40s
   

6. Use your Service object to access the Hello World application:

    curl <your-external-ip-address>:8080
   

   where <your-external-ip-address> is the external IP address of your service.

   The output is a hello message from the application:

    Hello Kubernetes!
   

   Note: If you are using Minikube, enter these commands:

    kubectl cluster-info
    kubectl describe services example-service
   

   The output displays the IP address of your Minikube node and the NodePort value for your service. Then enter this command to access the Hello World application:

    curl <minikube-node-ip-address>:<service-node-port>
   

   where <minikube-node-ip-address> us the IP address of your Minikube node, and <service-node-port> is the NodePort value for your service.

Using a service configuration file

As an alternative to using kubectl expose, you can use a service configuration file to create a Service.

What’s next

Learn more about connecting applications with services.