This blog will show how a simple Java application can talk to a database using service discovery in Kubernetes.

 Kubernetes Logo WildFly Logo

Service Discovery with Java and Database application in DC/OS explains why service discovery is an important aspect for a multi-container application. That blog also explained how this can be done for DC/OS.

Let’s see how this can be accomplished in Kubernetes with a single instance of application server and database server. This blog will use WildFly for application server and Couchbase for database.

This blog will use the following main steps:

  • Start Kubernetes one-node cluster
  • Kubernetes application definition
  • Deploy the application
  • Access the application

Start Kubernetes Cluster

Minikube is the easiest way to start a one-node Kubernetes cluster in a VM on your laptop. The binary needs to be downloaded first and then installed.

Complete installation instructions are available at github.com/kubernetes/minikube.

The latest release can be installed on OSX as as:

It also requires kubectl to be installed. Installing and Setting up kubectl provide detailed instructions on how to setup kubectl. On OSX, it can be installed as:

Now, start the cluster as:

The kubectl version command shows more details about the kubectl client and minikube server version:

More details about the cluster can be obtained using the kubectl cluster-info command:

Kubernetes Application Definition

Application definition is defined at github.com/arun-gupta/kubernetes-java-sample/blob/master/service-discovery.yml. It consists of:

  • A Couchbase service
  • Couchbase replica set with a single pod
  • A WildFly replica set with a single pod

The key part is where the value of the COUCHBASE_URI environment variable is name of the Couchbase service. This allows the application deployed in WildFly to dynamically discovery the service and communicate with the database.

arungupta/couchbase:travel Docker image is created using github.com/arun-gupta/couchbase-javaee/blob/master/couchbase/Dockerfile.

arungupta/wildfly-couchbase-javaee:travel Docker image is created using github.com/arun-gupta/couchbase-javaee/blob/master/Dockerfile.

Java EE application waits for database initialization to be complete before it starts querying the database. This can be seen at github.com/arun-gupta/couchbase-javaee/blob/master/src/main/java/org/couchbase/sample/javaee/Database.java#L25.

Deploy Application

This application can be deployed as:

The list of service and replica set can be shown using the command kubectl get svc,rs:

Logs for the single replica of Couchbase can be obtained using the command kubectl logs rs/couchbase-rs:

Logs for the WildFly replica set can be seen using the command kubectl logs rs/wildfly-rs:

Access Application

The kubectl proxy command starts a proxy to the Kubernetes API server. Let’s start a Kubernetes proxy to access our application:

Expose the WildFly replica set as a service using:

The list of services can be seen again using kubectl get svc command:

Now, the application is accessible at:

A formatted output looks like:

Now, new pods may be added as part of Couchbase service by scaling the replica set. Existing pods may be terminated or get rescheduled. But the Java EE application will continue to access the database service using the logical name.

This blog showed how a simple Java application can talk to a database using service discovery in Kubernetes.

For further information check out:

Posted by Arun Gupta, VP, Developer Advocacy, Couchbase

Arun Gupta is the vice president of developer advocacy at Couchbase. He has built and led developer communities for 10+ years at Sun, Oracle, and Red Hat. He has deep expertise in leading cross-functional teams to develop and execute strategy, planning and execution of content, marketing campaigns, and programs. Prior to that he led engineering teams at Sun and is a founding member of the Java EE team. Gupta has authored more than 2,000 blog posts on technology. He has extensive speaking experience in more than 40 countries on myriad topics and is a JavaOne Rock Star for three years in a row. Gupta also founded the Devoxx4Kids chapter in the US and continues to promote technology education among children. An author of several books on technology, an avid runner, a globe trotter, a Java Champion, a JUG leader, NetBeans Dream Team member, and a Docker Captain, he is easily accessible at @arungupta.

One Comment

  1. […] Service Discovery with Java and Database application in Kubernetes […]

Leave a reply