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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.

Download resources

Download deployment.yaml, service.yaml. These are plain k8s resources files one could add to a k8s cluster to run sbdemo.


DEMO_HOME=$(mktemp -d)
cd $DEMO_HOME

CONTENT=https://raw.githubusercontent.com/kinflate

# Get SpringBoot configs
for f in service deployment; do \
  wget -q $CONTENT/example-springboot/master/$f.yaml ; \
done

Initialize kustomize.yaml

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

Start this file:

touch $DEMO_HOME/kustomize.yaml

Add the resources

cd $DEMO_HOME

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

cat kustomize.yaml

kustomize.yaml's resources section should contain:

resources:
- service.yaml
- deployment.yaml

Add configmap generator

cd $DEMO_HOME
wget -q $CONTENT/example-springboot/master/application.properties
kustomize edit add configmap demo-configmap --from-file application.properties

cat kustomize.yaml

kustomize.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/v1beta2
kind: Deployment
metadata:
  name: sbdemo
spec:
  template:
    spec:
      containers:
        - name: sbdemo
          env:
          - name: spring.profiles.active
            value: prod
EOF

cat <<EOF >>$DEMO_HOME/kustomize.yaml
patches:
- patch.yaml
EOF

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 kustomize.yaml

kustomize.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-'

cat kustomize.yaml

kustomize.yaml should have updated value of namePrefix field:

namePrefix: prod-
objectAnnotations:
 note: This is a example annotation

This namePrefix directive adds prod- to all resource names.

kustomize build $DEMO_HOME

The output should contain:

apiVersion: v1
data:
  ....
kind: ConfigMap
metadata:
  ....
  name: prod-demo-configmap-7746248cmc
---
apiVersion: v1
kind: Service
metadata:
  ....
  name: prod-sbdemo
spec:
  ....
---
apiVersion: apps/v1beta2
kind: Deployment
metadata:
  ....
  name: prod-sbdemo
spec:
  selector:
    ....

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 label, but we can edit kustomize.yaml file under prod directory and add the production labels under objectLabels fields as highlighted below.

sed -i 's/app: helloworld/app: prod/' \
    $DEMO_HOME/kustomize.yaml

At this point, running kustomize build will generate MySQL configs with name-prefix 'prod-' and labels env:prod.

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.

cd $DEMO_HOME
wget -q $CONTENT/example-springboot-instances/master/production/memorylimit_patch.yaml

cat memorylimit_patch.yaml

The output contains

apiVersion: apps/v1beta2
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.

cd $DEMO_HOME
wget -q $CONTENT/example-springboot-instances/master/production/healthcheck_patch.yaml

cat healthcheck_patch.yaml