I want to create a simple spring boot app, and deploy it to Openshift 4.2. It supposed to be a straigh forward task, but the problem is that it is required to externalize all configuration to a configmaps or secret so no need to recompile the whole app in case of configuration change.

There are several approach of externalizing configuraton to configmaps, one way is put it as a string literal, include on your pod and call on application via environment variables, or deploy the whole configuration file and mount it on your Openshift pod. The last approach is the one that we will be doing now today.

First lets start with deploying our properties to Openshift as configmaps,

oc create cm myapp-api-configmap --from-file=D:\source\my-app\src\main\resources\application.properties

We can check and validate the result,

oc get cm

oc describe cm myapp-api-configmap

After that, we can mount corresponding configmap to a specific folder on our Pod, on below example modification is done on DeploymentConfig.yaml and mounting application.properties to /deployments/config folder.

kind: DeploymentConfig
apiVersion: apps.openshift.io/v1
metadata:
  ........
    spec:
      volumes:
        - name: myapp-api-configmap-volume
          configMap:
            name: myapp-api-configmap
            defaultMode: 420
      containers:
        - name: myapp-api
          image: >-
            image-registry.openshift-image-registry.svc:5000/openshift/myapp@sha256:1127.....
          ports:
            - containerPort: 8778
              protocol: TCP
            - containerPort: 8080
              protocol: TCP
            - containerPort: 8443
              protocol: TCP
          resources: {}
          volumeMounts:
            - name: myapp-api-configmap-volume
              mountPath: /deployments/config
          terminationMessagePath: /dev/termination-log
          terminationMessagePolicy: File
          imagePullPolicy: Always
      restartPolicy: Always
      terminationGracePeriodSeconds: 30
      dnsPolicy: ClusterFirst
      securityContext: {}
      schedulerName: default-scheduler

A modification is also needed on my Dockerfile, pointing a new path for my properties file by using “spring.config.location” parameter,

FROM registry.access.redhat.com/openjdk/openjdk-11-rhel7

USER jboss
RUN mkdir -p /deployments/image && chown -R jboss:0 /deployments
EXPOSE 8080

COPY target/application-1.0.jar /deployments/application.jar
CMD ["java", "-jar", "/deployments/application.jar", "--spring.config.location=file:///deployments/config/application.properties"]

Build, deploy,and see that application is now taking configuration from external configuration file.