Quick guide to deploying Java apps on OpenShift

In this article I’m going to show you how to deploy your applications on OpenShift (Minishift), connect them with other services exposed there or use some other interesting deployment features provided by OpenShift. Openshift is built on top of Docker containers and the Kubernetes container cluster orchestrator. Currently, it is the most popular enterprise platform basing on those two technologies, so it is definitely worth examining it in more details.

1. Running Minishift

We use Minishift to run a single-node OpenShift cluster on the local machine. The only prerequirement before installing MiniShift is the necessity to have a virtualization tool installed. I use Oracle VirtualBox as a hypervisor, so I should set --vm-driver parameter to virtualbox in my running command.

$  minishift start --vm-driver=virtualbox --memory=3G

2. Running Docker

It turns out that you can easily reuse the Docker daemon managed by Minishift, in order to be able to run Docker commands directly from your command line, without any additional installations. To achieve this just run the following command after starting Minishift.

@FOR /f "tokens=* delims=^L" %i IN ('minishift docker-env') DO @call %i

3. Running OpenShift CLI

The last tool, that is required before starting any practical exercise with Minishift is CLI. CLI is available under command oc. To enable it on your command-line run the following commands.

$ minishift oc-env
$ SET PATH=C:\Users\minkowp\.minishift\cache\oc\v3.9.0\windows;%PATH%
$ REM @FOR /f "tokens=*" %i IN ('minishift oc-env') DO @call %i

Alternatively you can use OpenShift web console which is available under port 8443. On my Windows machine it is by default launched under address 192.168.99.100.

4. Building Docker images of the sample applications

I prepared the two sample applications that are used for the purposes of presenting OpenShift deployment process. These are simple Java, Vert.x applications that provide HTTP API and store data in MongoDB. However, a technology is not very important now. We need to build Docker images with these applications. The source code is available on GitHub (https://github.com/piomin/sample-vertx-kubernetes.git) in branch openshift (https://github.com/piomin/sample-vertx-kubernetes/tree/openshift). Here’s sample Dockerfile for account-vertx-service.

FROM openjdk:8-jre-alpine
ENV VERTICLE_FILE account-vertx-service-1.0-SNAPSHOT.jar
ENV VERTICLE_HOME /usr/verticles
ENV DATABASE_USER mongo
ENV DATABASE_PASSWORD mongo
ENV DATABASE_NAME db
EXPOSE 8095
COPY target/$VERTICLE_FILE $VERTICLE_HOME/
WORKDIR $VERTICLE_HOME
ENTRYPOINT ["sh", "-c"]
CMD ["exec java -jar $VERTICLE_FILE"]

Go to account-vertx-service directory and run the following command to build image from a Dockerfile visible above.

$ docker build -t piomin/account-vertx-service .

The same step should be performed for customer-vertx-service. After it you have two images built, both in the same version latest, which now can be deployed and ran on Minishift.

5. Preparing OpenShift deployment descriptor

When working with OpenShift, the first step of application’s deployment is to create YAML configuration file. This file contains basic information about deployment like containers used for running applications (1), scaling (2), triggers that drive automated deployments in response to events (3) or a strategy of deploying your pods on the platform (4).

Deployment configurations can be managed with the oc command like any other resource. You can create new configuration or update the existing one by using oc apply command.

$ oc apply -f account-deployment.yaml

You can be surprised a little, but this command does not trigger any build and does not start the pods. In fact, you have only created a resource of type deploymentConfig, which may be describes deployment process. You can start this process using some other oc commands, but first let’s take a closer look on the resources required by our application.

6. Injecting environment variables

As I have mentioned before, our sample applications uses external datasource. They need to open the connection to the existing MongoDB instance in order to store there data passed using HTTP endpoints exposed by the application. Here’s MongoVerticle class, which is responsible for establishing client connection with MongoDB. It uses environment variables for setting security credentials and database name.

public class MongoVerticle extends AbstractVerticle {

	@Override
	public void start() throws Exception {
		ConfigStoreOptions envStore = new ConfigStoreOptions()
				.setType("env")
				.setConfig(new JsonObject().put("keys", new JsonArray().add("DATABASE_USER").add("DATABASE_PASSWORD").add("DATABASE_NAME")));
		ConfigRetrieverOptions options = new ConfigRetrieverOptions().addStore(envStore);
		ConfigRetriever retriever = ConfigRetriever.create(vertx, options);
		retriever.getConfig(r -> {
			String user = r.result().getString("DATABASE_USER");
			String password = r.result().getString("DATABASE_PASSWORD");
			String db = r.result().getString("DATABASE_NAME");
			JsonObject config = new JsonObject();
			config.put("connection_string", "mongodb://" + user + ":" + password + "@mongodb/" + db);
			final MongoClient client = MongoClient.createShared(vertx, config);
			final AccountRepository service = new AccountRepositoryImpl(client);
			ProxyHelper.registerService(AccountRepository.class, vertx, service, "account-service");
		});
	}

}

MongoDB is available in the OpenShift’s catalog of predefined Docker images. You can easily deploy it on your Minishift instance just by clicking “MongoDB” icon in “Catalog” tab. Username and password will be automatically generated if you do not provide them during deployment setup. All the properties are available as deployment’s environment variables and are stored as secrets/mongodb, where mongodb is the name of the deployment.

openshift-1

Environment variables can be easily injected into any other deployment using oc set command, and therefore they are injected into the pod after performing deployment process. The following command inject all secrets assigned to mongodb deployment to the configuration of our sample application’s deployment.

$ oc set env --from=secrets/mongodb dc/account-service

7. Importing Docker images to OpenShift

A deployment configuration is ready. So, in theory we could have start deployment process. However, we have back for a moment to the deployment config defined in the Step 5. We defined there two triggers that causes a new replication controller to be created, what results in deploying new version of pod. First of them is a configuration change trigger that fires whenever changes are detected in the pod template of the deployment configuration (ConfigChange). The second of them, image change trigger (ImageChange) fires when a new version of the Docker image is pushed to the repository. To be able to watch if an image in repository has been changed, we have to define and create image stream. Such an image stream does not contain any image data, but present a single virtual view of related images, something similar to an image repository. Inside deployment config file we referred to image stream account-vertx-service, so the same name should be provided inside image stream definition. In turn, when setting the spec.dockerImageRepository field we define the Docker pull specification for the image.

Finally, we can create resource on OpenShift platform.

$ oc apply -f account-image.yaml

8. Running deployment

Once a deployment configuration has been prepared, and Docker images has been succesfully imported into repository managed by OpenShift instance, we may trigger the build using the following oc command.

$ oc rollout latest dc/account-service
$ oc rollout latest dc/customer-service

If everything goes fine the new pods should be started for the defined deployments. You can easily check it out using OpenShift web console.

9. Updating image stream

We have already created two image streams related to the Docker repositories. Here’s the screen from OpenShift web console that shows the list of available image streams.

openshift-images

To be able to push a new version of an image to OpenShift internal Docker registry we should first perform docker login against this registry using user’s authentication token. To obtain the token from OpenShift use oc whoami command, and then pass it to your docker login command with -p parameter.

$ oc whoami -t
Sz9_TXJQ2nyl4fYogR6freb3b0DGlJ133DVZx7-vMFM
$ docker login -u developer -p Sz9_TXJQ2nyl4fYogR6freb3b0DGlJ133DVZx7-vMFM https://172.30.1.1:5000

Now, if you perform any change in your application and rebuild your Docker image with latest tag, you have to push that image to image stream on OpenShift. The address of internal registry has been automatically generated by OpenShift, and you can check it out in the image stream’s details. For me, it is 172.30.1.1:5000.

$ docker tag piomin/account-vertx-service 172.30.1.1:5000/sample-deployment/account-vertx-service:latest
$ docker push 172.30.1.1:5000/sample-deployment/account-vertx-service

After pushing new version of Docker image to image stream, a rollout of application is started automatically. Here’s the screen from OpenShift web console that shows the history of account-service application deployments.

openshift-2

Conclusion

I have shown you the further steps of deploying your application on the OpenShift platform. Basing on sample Java application that connects to a database, I illustrated how to inject credentials to that application’s pod entirely transparently for a developer. I also perform an update of application’s Docker image, in order to show how to trigger a new version deployment on image change.

openshift-3

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Author: Piotr Mińkowski

IT Architect, Java Software Developer

One thought on “Quick guide to deploying Java apps on OpenShift”

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