hello-world JVM Checkpoint/Restore demo for SpringOne at VMware Explore 2023

This repo provides a simple Hello World sample project for Spring Boot.

It can be deployed locally or to a Kubernetes cluster utilizing Coordinated Restore at Checkpoint (CRaC) as provided by the Azul Zulu builds of OpenJDK with CRaC support.

Local run

To run the app locally using the embedded Tomcat server you can run this command:

./mvnw spring-boot:run

You can modify the default message "World" using an application property of app.message:

/mvnw spring-boot:run -Dspring-boot.run.arguments="--app.message=Test"

Build image and push to Docker Hub

First, set the REGISTRY_PREFIX env var to your preferred registry and account to use.

export REGISTRY_PREFIX='docker.io/springdeveloper'

NOTE: This build can be run on X86-64 as well as ARM-64 based systems and you can specify the target architecture to use as amd64 for X86-64 based systems or as arm64 for ARM based ones.

To specify the target architecture of the system where you will run the app, set the TARGET_ARCH environment variable. For x64_64 based systems set:

export TARGET_ARCH=amd64

and, for ARM based systems set:

export TARGET_ARCH=arm64

Build the image

To build the image run the build.sh script.

./build.sh

This will build and push the image to registry and account specified above in the REGISTRY_PREFIX env var.

Running locally using Docker

This will create a cracvol volume where the checkpoint files will be written.

To start the container run:

Note: This requires a few additional capabilities beyond the ones you automatically get from Docker.

docker run -it --rm -p 8080:8080 -e CRAC_FILES_DIR=/crac/hello-world --name hello-world \
  --mount source=cracvol,target=/crac \
  --cap-add CHECKPOINT_RESTORE --cap-add NET_ADMIN --cap-add SYS_PTRACE --cap-add SYS_ADMIN \
  ${REGISTRY_PREFIX}/hello-world:${TARGET_ARCH}-$(cat VERSION)

If you kill the hello-world container you will notice that the next time you start it, it will restore the files from the attached cracvol volume.

Running in a Kubernetes cluster

Create the NFS server for the checkpoint files

Note: different providers use different storage class names. Use one that is available on your cluste, typically "default" or "standard".

To create a PVC and an NFS server for storing the checkpoint files, run:

ytt -f crac-nfs \
  --data-value=storage_class_name=standard | \
kubectl apply -f -

Use a Kubernetes Deployment and Service

Running as a Kubernetes deployment and service

Deploying the app

To create the deployment that will restore from the checkpoint and the service, run the following:

ytt -f kubernetes \
  --data-value=registry_prefix=$REGISTRY_PREFIX \
  --data-value=arch=$TARGET_ARCH \
  --data-value=version=$(cat VERSION) \
  --data-value=nfs_server_ip=$(kubectl get service nfs-server -o jsonpath='{.spec.clusterIP}') | \
kapp deploy -a hello-world -y -f -

Accessing the app deployed to your cluster

The service is configured for a NodePort so you can use port forward to access the app:

kubectl port-forward svc/hello-world 8080:80

Then, in a different terminal run:

APP_URL=http://localhost:8080
curl $APP_URL

Scaling the deployment replicas

To scale the deployment replicas to zero use:

kubectl scale deployment/hello-world --replicas=0

To scale the deployment back up use:

kubectl scale deployment/hello-world --replicas=1

Deploying as a Knative service

Configure Knative

Update the Knative configuration with the following features enabled:

  kubernetes.podspec-securitycontext: Enabled
  kubernetes.containerspec-addcapabilities: Enabled
  kubernetes.podspec-persistent-volume-claim: Enabled
  kubernetes.podspec-persistent-volume-write: Enabled
  kubernetes.podspec-fieldref: Enabled

Use this command to edit the config:

kubectl edit configmap/config-features -n knative-serving

Deploy Knative service

To create the Knative service that will checkpoint and then restore from the checkpoint, run the following:

ytt -f knative \
  --data-value=registry_prefix=$REGISTRY_PREFIX \
  --data-value=arch=$TARGET_ARCH \
  --data-value=version=$(cat VERSION) \
  --data-value=nfs_server_ip=$(kubectl get service nfs-server -o jsonpath='{.spec.clusterIP}') | \
kubectl create -f -

Accessing the app deployed to your cluster

Determine the URL to use for the accessing the app by running:

kn service list

or, using kubectl:

kubectl get service.serving.knative.dev

To access the deployed app use the URL shown under "Workload Knative Services".

APP_URL=<Knative-service-URL>

Then, use curl or some other utility to access the URL:

curl $APP_URL

Deploying as a TAP workload

TBD, not working yet

Deploy TAP workload from the image

To create the TAP workload that will restore from the checkpoint, run the following:

ytt -f config/workload.yaml \
  --data-value=registry_prefix=$REGISTRY_PREFIX \
  --data-value=arch=$TARGET_ARCH \
  --data-value=version=$(cat VERSION) | \
kubectl apply -f -

Accessing the app deployed to your cluster

Determine the URL to use for the accessing the app by running:

tanzu apps workload get hello-world

To access the deployed app use the URL shown under "Knative Services".

export APP_URL=<Knative-service-URL>

Then, use curl or some other utility to access the URL:

curl APP_URL