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Demo: SpringBoot

In this tutorial, you will learn - how to use kustomize to customize a basic Spring Boot application's k8s configuration for production use cases.

In the production environment we want to customize the following:

  • add application specific configuration for this Spring Boot application
  • configure prod DB access configuration
  • resource names to be prefixed by 'prod-'.
  • resources to have 'env: prod' labels.
  • JVM memory to be properly set.
  • health check and readiness check.

First make a place to work:

DEMO_HOME=$(mktemp -d)

Download resources

To keep this document shorter, the base resources needed to run springboot on a k8s cluster are off in a supplemental data directory rather than declared here as HERE documents.

Download them:

CONTENT="https://raw.githubusercontent.com\
/kubernetes-sigs/kustomize\
/master/examples/springboot"

curl -s -o "$DEMO_HOME/#1.yaml" \
  "$CONTENT/base/{deployment,service}.yaml"

Initialize kustomization.yaml

The kustomize program gets its instructions from a file called kustomization.yaml.

Start this file:

touch $DEMO_HOME/kustomization.yaml

Add the resources

cd $DEMO_HOME

kustomize edit add resource service.yaml
kustomize edit add resource deployment.yaml

cat kustomization.yaml

kustomization.yaml's resources section should contain:

resources:
- service.yaml
- deployment.yaml

Add configMap generator

echo "app.name=Kustomize Demo" >$DEMO_HOME/application.properties

kustomize edit add configmap demo-configmap \
  --from-file application.properties

cat kustomization.yaml

kustomization.yaml's configMapGenerator section should contain:

configMapGenerator:
- files:
  - application.properties
  name: demo-configmap

Customize configMap

We want to add database credentials for the prod environment. In general, these credentials can be put into the file application.properties. However, for some cases, we want to keep the credentials in a different file and keep application specific configs in application.properties. With this clear separation, the credentials and application specific things can be managed and maintained flexibly by different teams. For example, application developers only tune the application configs in application.properties and operation teams or SREs only care about the credentials.

For Spring Boot application, we can set an active profile through the environment variable spring.profiles.active. Then the application will pick up an extra application-<profile>.properties file. With this, we can customize the configMap in two steps. Add an environment variable through the patch and add a file to the configMap.

cat <<EOF >$DEMO_HOME/patch.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: sbdemo
spec:
  template:
    spec:
      containers:
        - name: sbdemo
          env:
          - name: spring.profiles.active
            value: prod
EOF

kustomize edit add patch patch.yaml

cat <<EOF >$DEMO_HOME/application-prod.properties
spring.jpa.hibernate.ddl-auto=update
spring.datasource.url=jdbc:mysql://<prod_database_host>:3306/db_example
spring.datasource.username=root
spring.datasource.password=admin
EOF

kustomize edit add configmap \
  demo-configmap --from-file application-prod.properties

cat kustomization.yaml

kustomization.yaml's configMapGenerator section should contain:

configMapGenerator:
- files:
  - application.properties
  - application-prod.properties
  name: demo-configmap

Name Customization

Arrange for the resources to begin with prefix prod- (since they are meant for the production environment):

cd $DEMO_HOME
kustomize edit set nameprefix 'prod-'

kustomization.yaml should have updated value of namePrefix field:

namePrefix: prod-

This namePrefix directive adds prod- to all resource names, as can be seen by building the resources:

kustomize build $DEMO_HOME | grep prod-

Label Customization

We want resources in production environment to have certain labels so that we can query them by label selector.

kustomize does not have edit set label command to add a label, but one can always edit kustomization.yaml directly:

cat <<EOF >>$DEMO_HOME/kustomization.yaml
commonLabels:
  env: prod
EOF

Confirm that the resources now all have names prefixed by prod- and the label tuple env:prod:

kustomize build $DEMO_HOME | grep -C 3 env

Download Patch for JVM memory

When a Spring Boot application is deployed in a k8s cluster, the JVM is running inside a container. We want to set memory limit for the container and make sure the JVM is aware of that limit. In K8s deployment, we can set the resource limits for containers and inject these limits to some environment variables by downward API. When the container starts to run, it can pick up the environment variables and set JVM options accordingly.

Download the patch memorylimit_patch.yaml. It contains the memory limits setup.

curl -s  -o "$DEMO_HOME/#1.yaml" \
  "$CONTENT/overlays/production/{memorylimit_patch}.yaml"

cat $DEMO_HOME/memorylimit_patch.yaml

The output contains

apiVersion: apps/v1
kind: Deployment
metadata:
  name: sbdemo
spec:
  template:
    spec:
      containers:
        - name: sbdemo
          resources:
            limits:
              memory: 1250Mi
            requests:
              memory: 1250Mi
          env:
          - name: MEM_TOTAL_MB
            valueFrom:
              resourceFieldRef:
                resource: limits.memory

Download Patch for health check

We also want to add liveness check and readiness check in the production environment. Spring Boot application has end points such as /actuator/health for this. We can customize the k8s deployment resource to talk to Spring Boot end point.

Download the patch healthcheck_patch.yaml. It contains the liveness probes and readyness probes.

curl -s  -o "$DEMO_HOME/#1.yaml" \
  "$CONTENT/overlays/production/{healthcheck_patch}.yaml"

cat $DEMO_HOME/healthcheck_patch.yaml

The output contains

apiVersion: apps/v1
kind: Deployment
metadata:
  name: sbdemo
spec:
  template:
    spec:
      containers:
        - name: sbdemo
          livenessProbe:
            httpGet:
              path: /actuator/health
              port: 8080
            initialDelaySeconds: 10
            periodSeconds: 3
          readinessProbe:
            initialDelaySeconds: 20
            periodSeconds: 10
            httpGet:
              path: /actuator/info
              port: 8080

Add patches

Add these patches to the kustomization:

cd $DEMO_HOME
kustomize edit add patch memorylimit_patch.yaml
kustomize edit add patch healthcheck_patch.yaml

kustomization.yaml should have patches field:

patchesStrategicMerge:
- patch.yaml
- memorylimit_patch.yaml
- healthcheck_patch.yaml

The output of the following command can now be applied to the cluster (i.e. piped to kubectl apply) to create the production environment.

kustomize build $DEMO_HOME  # | kubectl apply -f -