"Knative Serving" for Spring Boot Applications

I got a chance to try Knative's Serving feature to deploy a Spring Boot application and this post is simply documenting a sample and the approach I took.

I don't understand the internals of Knative enough yet to have an opinion on whether this approach is better than the deployment + services + ingress based approach.

One feature that is awesome is the auto-scaling feature in Knative Serving, which based on the load, increases/decreases the number of pods as part of a "Deployment" handling the request.

Details of the Sample

My entire sample is available here and it is mostly developed based on the java sample available with Knative Serving documentation. I used Knative with a minikube environment to try the sample.

Deploying to Kubernetes/Knative

Assuming that a Kubernetes environment with Istio and Knative has been set-up, the way to run the application is to deploy a Kubernetes manifest this way:

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:
  name: sample-boot-knative-service
  namespace: default
spec:
  runLatest:
    configuration:
      revisionTemplate:
        spec:
          container:
            image: bijukunjummen/sample-boot-knative-app:0.0.1-SNAPSHOT

The image "bijukunjummen/sample-boot-knative-app:0.0.1-SNAPSHOT" is publicly available via Dockerhub, so this sample should work out of the box.

Applying this manifest:

kubectl apply -f service.yml

should register a Knative Serving Service resource with Kubernetes, the Knative serving services resource manages the lifecycle of other Knative resources (configuration, revision, route) the details of which can be viewed using the following commands, if anything goes wrong, the details should show up in the output:

kubectl get services.serving.knative.dev sample-boot-knative-service -o yaml

Testing

Assuming that the Knative serving service is deployed cleanly, the first oddity to see is that no pods show up for the application!

If I were to make a request to the app now, which is done via a routing layer managed by Knative - this can be retrieved for a minikube environment using the following bash script:

export GATEWAY_URL=$(echo $(minikube ip):$(kubectl get svc knative-ingressgateway -n istio-system -o 'jsonpath={.spec.ports[?(@.port==80)].nodePort}'))
export APP_DOMAIN=$(kubectl get services.serving.knative.dev sample-boot-knative-service  -o="jsonpath={.status.domain}")

and making a call to an endpoint of the app using CUrl:

curl -X "POST" "http://${GATEWAY_URL}/messages" \
     -H "Accept: application/json" \
     -H "Content-Type: application/json" \
     -H "Host: ${APP_DOMAIN}" \
     -d $'{
  "id": "1",
  "payload": "one",
  "delay": "300"
}'

OR httpie

http http://${GATEWAY_URL}/messages Host:"${APP_DOMAIN}" id=1 payload=test delay=100

should magically, using the auto-scaler component start spinning up the pods to handle the request:

The first request took almost 17 seconds to complete, the time it takes to spin up a pod, but subsequent requests are quick.

Now, to show the real power of auto-scaler I ran a small load test with a 50 user load and pods are scaled up and down as required.

Conclusion

I can see the promise of Knative in automatically managing the resources, once defined using a fairly simple manifest, in a Kubernetes environment and letting a developer focus on the code and logic.

Jib - Building docker image for a Spring Boot App

I was pleasantly surprised by how easy it was to create a docker image for a sample Spring Boot application using Jib.

Let me first contrast Jib with an approach that I was using before.

I was creating docker images using bmuschko's excellent gradle-docker plugin. Given access to a docker daemon and a gradle dsl based description of the Dockerfile or a straight Dockerfile, it would create the docker image using a gradle task. In my case, the task to create the docker image looks something like this:

task createDockerImage(type: DockerBuildImage) {
    inputDir = file('.')
    dockerFile = project.file('docker/Dockerfile')
    tags = ['sample-micrometer-app:' + project.version]
}

createDockerImage.dependsOn build

and my Dockerfile itself derived off "java:8" base image:

FROM java:8
...

gradle-docker-plugin made it simple to create a docker image right from gradle with the catch that the plugin needs access to a docker daemon to create the image. Also since the base "java:8" image is large the final docker image turns out to be around 705MB on my machine. Again no fault of the gradle-docker plugin but based on my choice of base image.


Now with Jib, all I have to do is to add the plugin:

plugins {
    id 'com.google.cloud.tools.jib' version '0.9.6'
}

Configure it to give the image a name:

jib {
    to {
        image = "sample-micrometer-app:0.0.1-SNAPSHOT"
    }
}

And that is it. With a local docker daemon available, I can create my docker image using the following task:

./gradlew jibDockerBuild

Jib automatically selects a very lightweight base image - my new image is just about 150 MB in size.

If I had access to a docker registry available then the local docker daemon is not required, it can directly create and publish the image to a docker registry!

Jib gradle plugin provides an interesting task - "jibExportDockerContext" to export out the docker file, this way if needed a docker build can be run using this Dockerfile, for my purposes I wanted to see the contents of this file and it looks something like this:

FROM gcr.io/distroless/java

COPY libs /app/libs/
COPY resources /app/resources/
COPY classes /app/classes/

ENTRYPOINT ["java","-cp","/app/libs/*:/app/resources/:/app/classes/","sample.meter.SampleServiceAppKt"]

All in all, a very smooth experience and Jib does live up to its goals. My sample project with jib integrated with a gradle build is available here.