= Configuring Spring Boot Application on Kubernetes with ConfigMaps

A demo Spring Boot application that demonstrates on using Kubernetes https://kubernetes.io/docs/tasks/configure-pod-container/configmap/[ConfigMaps] to configure Spring Boot application.

== Setup

• You might need an access to Kubernetes Cluster to play with this application. The easiest way to get local Kuberentes cluster up and running is using https://github.com/kubernetes/minikube[minikube]

• Install https://docs.spring.io/spring-boot/docs/current/reference/html/getting-started-installing-spring-boot.html#getting-started-installing-the-cli[Spring Boot CLI]

• Untar/Unzip Spring Boot CLI 1.5.7.RELEASE and add it your path

NOTE: The rest of the document assumes you have https://github.com/kubernetes/minikube[minikube] up and running

== Build and Deploy

=== Create project

For the demo purpose we will be creating a simple Spring Boot project,

[source,sh]

spring init --artifactId=spring-boot-configmaps-demo
--name="Kubernetes:: Spring Boot:: Demos :: ConfigMaps Demo"
--groupId="com.redhat.developers"
--package-name="com.redhat.developers"
--dependencies=web,actuator,lombok
--extract spring-boot-configmaps-demo <1>

cd spring-boot-configmaps-demo

./mvnw io.fabric8:fabric8-maven-plugin:3.5.30:setup <2>

<1> Creates a Spring Boot project with web and actuator dependencies <2> Adds the https://maven.fabric8.io[fabric8-maven-plugin] to the project that will help with deploying the application on Kubernetes

The complete demo sources is available https://github.com/redhat-developer-demos/spring-boot-configmaps-demo[here]

The directory spring-boot-configmaps-demo will be referred to as $PROJECT_HOME throughout this document.

==== Add a simple Greeting REST API

[source,java]

package com.redhat.developers;

import lombok.extern.slf4j.Slf4j; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController;

@RestController @Slf4j public class GreeterController {

@GetMapping("/greet/{user}")
public String greet(@PathVariable("user") String user) {
    String prefix = System.getenv().getOrDefault("GREETING_PREFIX", "Hi"); <1>
    log.info("Prefix :{} and User:{}", prefix, user);
    if (prefix == null) {
        prefix = "Hello!";
    }

    return String.format("%s %s! Welcome to Configuring Spring Boot on Kubernetes!", prefix, user);
}

}

<1> The application looks for the prefix from an environment variable called GREETER_PREFIX

[[configmap-as-env-vars]] === ConfigMap Properties as Environment Variables

Lets create a Kubernetes https://kubernetes.io/docs/tasks/configure-pod-container/configmap/[ConfigMaps] to hold the property called greeter.prefix, which will then be injected to Kubernetes deployment via an environment variable called GREETER_PREFIX

[[create-configmap]] ==== Create ConfigMap

[source,sh]

kubectl create configmap spring-boot-configmaps-demo --from-literal=greeter.prefix="Hello" <1>

kubectl get configmap spring-boot-configmaps-demo -oyaml <2>

<1> Creates a configmap called spring-boot-configmaps-demo which will have property called greeter.prefix with a value "Hello" <2> Displays the ConfigMap called spring-boot-configmaps-demo as yaml

Example output of kubectl get configmap spring-boot-configmaps-demo -oyaml

[source,yaml]

apiVersion: v1 data: greeter.prefix: Hello kind: ConfigMap metadata: creationTimestamp: 2017-09-19T04:03:37Z name: spring-boot-configmaps-demo namespace: default resourceVersion: "50671" selfLink: /api/v1/namespaces/default/configmaps/spring-boot-configmaps-demo uid: 8397deb7-9cef-11e7-9b8d-080027da6995

==== Kubernetes Manifests

As the application is configured to use https://maven.fabric8.io[fabric8-maven-plugin], we can create Kubernetes deployment and service as fragments in $PROJECT_HOME/src/main/fabric8. The https://maven.fabric8.io[fabric8-maven-plugin] takes care of building the complete Kubernetes manifests by merging the contents of the fragment(s) from $PROJECT_HOME/src/main/fabric8 during deploy.

===== Deployment Create a file called deployment.yaml in $PROJECT_HOME/src/main/fabric8 with the following contents,

[source,yaml]

spec: template: spec: containers: - env: - name: GREETING_PREFIX <1> valueFrom: configMapKeyRef: <2> name: spring-boot-configmaps-demo <3> key: greeter.prefix <4>

<1> Define Environment variable called GREETING_PREFIX <2> Defines that the value will be a ConfigMap reference <3> Name of the ConfigMap from where to look for the key/value pair, this should be same name you have used in <> <4> The property key inside the ConfigMap, whose value needs to be assigned to environment variable GREETING_PREFIX

===== Service

To enable easy access of the application, we make the type of Kubernetes service as https://kubernetes.io/docs/concepts/services-networking/service/#type-nodeport[NodePort], create a file called svc.yaml in $PROJECT_HOME/src/main/fabric8 with the following contents,

[source,yaml]

apiVersion: v1 kind: Service spec: type: NodePort <1>

<1> expose the service using https://kubernetes.io/docs/concepts/services-networking/service/#type-nodeport[NodePort]

[[deploy-app]] ==== Deploy

To deploy the application execute the command ./mvnw clean fabric8:deploy. The application deployment status can be checked using the command kubectl get pods -w

[[access-app]] ==== Access the Application

To access and test the application execute the following command,

[source,sh]

curl $(minikube service spring-boot-configmaps-demo --url)/greet/jerry; echo "";

The above command should display a message like Hello jerry! Welcome to Configuring Spring Boot on Kubernetes!

NOTE: minikube service spring-boot-configmaps-demo --url is used to get the service url and port via which we can access the application

=== As File Mounts

In <> we saw how Kubernetes https://kubernetes.io/docs/tasks/configure-pod-container/configmap/[ConfigMaps] can be injected to the Kubernetes deployment as environment variables. In this section we will see how we can mount Spring Boot application.yaml using https://kubernetes.io/docs/tasks/configure-pod-container/configmap/[ConfigMaps].

[[app-properties]] ==== Add property to application.properties

Add a property called greeter.message to the $PROJECT_HOME/src/main/resources/application.properties. The modified file is as shown below,

[source]

greeter.message=%s %s! Spring Boot application.properties has been mounted as volume on Kubernetes!

[[create-configmap-file]] ==== Create ConfigMap

[source,sh]

cd $PROJECT_HOME kubectl create configmap spring-app-config --from-file=src/main/resources/application.properties <1>

<1> This is similar to creating <<create-configmap,ConfigMap>> but instead of literal we will now put the entire file application.properties in a configmap called spring-app-config

To see the contents of the ConfigMap, execute the command kubectl get configmap spring-app-config -oyaml, a sample output is shown below,

[source,yaml]

apiVersion: v1 data: application.properties: greeter.message=%s %s! Spring Boot application.properties has been mounted as volume on Kubernetes! on Kubernetes! kind: ConfigMap metadata: creationTimestamp: 2017-09-19T04:45:27Z name: spring-app-config namespace: default resourceVersion: "53471" selfLink: /api/v1/namespaces/default/configmaps/spring-app-config uid: 5bac774a-9cf5-11e7-9b8d-080027da6995

==== Update GreeterController to use greeter.message

Modify the GreeterController to use the greeter.message, the modified file looks as shown below

[source,java]

package com.redhat.developers;

import lombok.extern.slf4j.Slf4j; import org.springframework.beans.factory.annotation.Value; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController;

@RestController @Slf4j public class GreeterController {

@Value("${greeter.message}")
private String greeterMessageFormat; <1>

@GetMapping("/greet/{user}")
public String greet(@PathVariable("user") String user) {
    String prefix = System.getenv().getOrDefault("GREETING_PREFIX", "Hi");
    log.info("Prefix :{} and User:{}", prefix, user);
    if (prefix == null) {
        prefix = "Hello!";
    }

    return String.format(greeterMessageFormat, prefix, user);
}

}

<1> Injects the property greeter.message which has been defined in application.properties

===== Mounting application.properties inside Deployment

Kubernetes https://kubernetes.io/docs/tasks/configure-pod-container/configmap/[ConfigMaps] can be mounted as volumes inside the deployments.

Update the $PROJECT_HOME/src/main/fabric8/deployment.yaml with the following contents,

[source,yaml]

spec: template: spec: containers: - env: - name: GREETING_PREFIX valueFrom: configMapKeyRef: name: spring-boot-configmaps-demo key: greeter.prefix volumeMounts: - name: application-config <1> mountPath: "/deployments/config" <2> readOnly: true volumes: - name: application-config configMap: name: spring-app-config <3> items: - key: application.properties <4> path: application.properties <5>

<1> Define a Volume mount and give it a logical name <2> Define mountPath, location inside container where the file will be mounted <3> The ConfigMap to be used, this name should be same as defined in <<create-configmap-file,ConfigMap from file>> <4> The property key from ConfigMap to be used as a content of file <5> The sub path within location defined, in this case it will be /deployments/config/application.properties

==== Deploy and Access the application

<> and <> to see the application.properties loaded and used from ConfigMaps via container volumes.

When you access the application you will notice the response to be Hello jerry! Spring Boot application.properties has been mounted as volume on Kubernetes!

[TIP]

To check if the volume has been mounted execute the command,

[source,sh]

kubectl exec spring-boot-configmaps-demo-3812387281-f566v -- cat /deployments/config/application.properties <1>

<1> Replace the pod id spring-boot-configmaps-demo-3812387281-f566v with pod from your local setup, the pod id is retrieved using the command kubectl get pod

====

=== Cleanup

To clean the deployments from $PROJECT_HOME execute ./mvnw fabric8:undeploy

--END--