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:
To check the version, enter kubectl version.
Creating a Service for an application running in two pods
-
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 -
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 -
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 -
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. -
Display the IP addresses for your service:
kubectl get services example-serviceThe 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 -
Use your Service object to access the Hello World application:
curl <your-external-ip-address>:8080where
<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-serviceThe 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.