java.adoc

Lab: Deploying Java Code

Application Description

In this lab, we’re going to deploy a backend service, developed in Java programming language that will expose 2 main REST endpoints to the visualizer application (parksmap web component that was deployed in the previous labs). The application will query for national parks information (including it’s coordinates) that is stored in a Mongo database. This application will also provide an external access point, so that the API provided can be directly used by the end user.

Background: Source-to-Image (S2I)

In a previous lab, we learned how to deploy a pre-existing Docker-formatted image. Now we will expand on that a bit by learning how OpenShift builds a Docker images using source code from an existing repository.

Source-to-Image (S2I) is another open source project sponsored by Red Hat. Its goal:

Source-to-image (S2I) is a tool for building reproducible Docker images. S2I
produces ready-to-run images by injecting source code into a Docker image and
assembling a new Docker image which incorporates the builder image and built
source. The result is then ready to use with docker run. S2I supports
incremental builds which re-use previously downloaded dependencies, previously
built artifacts, etc.

OpenShift is S2I-enabled and can use S2I as one of its build mechanisms (in addition to building Docker images from Dockerfiles, and "custom" builds).

OpenShift runs the S2I process inside a special Pod, called a Build Pod, and thus builds are subject to quotas, limits, resource scheduling, and other aspects of OpenShift.

A full discussion of S2I is beyond the scope of this class, but you can find more information about it either in the OpenShift S2I documentation or on GitHub (following the link above). The only key concept you need to remember about S2I is that it’s magic.

Exercise: Creating a Java application

The backend service that we will be deploying as part of this exercise is called nationalparks. This is a Java Spring Boot application that performs 2D geo-spatial queries against a MongoDB database to locate and return map coordinates of all National Parks in the world. That was just a fancy way of saying that we are going to deploy a webservice that returns a JSON list of places.

Add to Project

Because the nationalparks application is a back-end to serve data that our existing front-end will consume, we are going to build it inside the existing {{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}} project. And, we will do it from the web console.

Using application code on embedded GitLab

OpenShift can work with any accessible Git repository. This could be GitHub, GitLab, or any other server that speaks Git. You can even register webhooks in your Git server to initiate OpenShift builds triggered by any update to the application code!

The repository that we are going to use is already cloned in the internal GitLab repository and located at the following URL:

http://{{GITLAB_URL_PREFIX}}.{{ROUTER_ADDRESS}}/{{GITLAB_USER}}/nationalparks/tree/{{NATIONALPARKS_VERSION}}

Note	Your GitLab credentials are: {{GITLAB_USER}}/{{GITLAB_PASSWORD}}

Later in the lab, we want you to make a code change and then rebuild your application. This is a fairly simple Spring framework Java application.

Build the Code on OpenShift

Similar to how we used "Add to project" before with a Docker-formatted image, we can do the same for specifying a source code repository. Since for this lab you have your own GitLab repository, let’s use it with a simple Java S2I image.

In the OpenShift web console, find your {{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}} project, and then click the "Add to Project" button. You will see a list of categories of runtimes, and other types of components that you can deploy and run on OpenShift.

Type "jdk" into the search box, and then select the item titled redhat-openjdk18-openshift.

After you click redhat-openjdk18-openshift, on the next screen you will need to enter a name and a Git repository URL. For the name, enter nationalparks, and for the Git repository URL, enter:

http://{{GITLAB_URL_PREFIX}}.{{ROUTER_ADDRESS}}/{{GITLAB_USER}}/nationalparks.git

Note	All of these runtimes shown are made available via Templates and ImageStreams, which will be discussed in a later lab.

These labs were written against specific points in time for these applications. With Git as our version control system (VCS), we are using the concept of Branches/Tags. Click on Show advanced routing, build, and deployment options. In the Git Reference field enter "{{NATIONALPARKS_VERSION}}". This will cause the S2I process to grab that specific tag in the code repository.

{% if USE_MAVEN %}

To speed build process, a Sonatype Nexus server is running in the environment that will cache your dependencies as you pull them down. To use it, you need to scroll down to Build Configuration and add an environment variable named MAVEN_MIRROR_URL with value http://nexus.workshop-infra.svc.cluster.local:8081/content/groups/public

{% endif %}

You can then hit the button labeled "Create". Then click Continue to overview. You will see this in the web console:

Build nationalparks, #1 Running. A new deployment will be created automatically
once the build completes.  a few seconds ago View Log

Go ahead and click "View Log". This is a Java-based application that uses Maven as the build and dependency system. For this reason, the initial build will take a few minutes as Maven downloads all of the dependencies needed for the application. You can see all of this happening in real time!

From the command line, you can also see the Builds:

$ oc get builds

You’ll see output like:

NAME              TYPE      FROM          STATUS     STARTED              DURATION
nationalparks-1   Source    Git@b052ae6   Running    About a minute ago   1m2s

You can also view the build logs with the following command:

$ oc logs -f builds/nationalparks-1

After the build has completed and successfully:

• The S2I process will push the resulting Docker-formatted image to the internal OpenShift registry

• The DeploymentConfiguration (DC) will detect that the image has changed, and this will cause a new deployment to happen.

• A ReplicationController (RC) will be spawned for this new deployment.

• The RC will detect no Pods are running and will cause one to be deployed, as our default replica count is just 1.

In the end, when issuing the oc get pods command, you will see that the build Pod has finished (exited) and that an application Pod is in a ready and running state:

NAME                    READY     STATUS      RESTARTS   AGE
nationalparks-1-tkid3   1/1       Running     3          2m
nationalparks-1-build   0/1       Completed   0          3m
parksmap-1-4hbtk        1/1       Running     0          2h

If you look again at the web console, you will notice that, when you create the application this way, OpenShift also creates a Route for you. You can see the URL in the web console, or via the command line:

$ oc get routes

Where you should see something like the following:

NAME            HOST/PORT                                                   PATH      SERVICES        PORT       TERMINATION
nationalparks   nationalparks-{{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}}.{{ROUTER_ADDRESS}}             nationalparks   8080-tcp
parksmap        parksmap-{{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}}.{{ROUTER_ADDRESS}}                  parksmap        8080-tcp

In the above example, the URL is:

http://nationalparks-{{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}}.{{ROUTER_ADDRESS}}

Since this is a back-end application, it doesn’t actually have a web interface. However, it can still be used with a browser. All back ends that work with the parks map front end are required to implement a /ws/info/ endpoint. To test, the complete URL to enter in your browser is:

http://nationalparks-{{EXPLORE_PROJECT_NAME}}{{USER_SUFFIX}}.{{ROUTER_ADDRESS}}/ws/info/

Warning

The trailing slash is required.

You will see a simple JSON string:

{"id":"nationalparks","displayName":"National Parks","center":{"latitude":"47.039304","longitude":"14.505178"},"zoom":4}

Earlier we said:

This is a Java Spring Boot application that performs 2D geo-spatial queries
against a MongoDB database

But we don’t have a database. Yet.