Hello World - Kotlin

    Follow the steps below to create the sample code and then deploy the app to your cluster. You can also download a working copy of the sample, by running the following commands:

    • A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions if you need to create one.
    • installed and running on your local machine, and a Docker Hub account configured (we’ll use it for a container registry).

    1. Create a new directory and cd into it:

      1. mkdir hello
      2. cd hello

    2. Create a file named Main.kt at src/main/kotlin/com/example/hello and copy the code block below into it:

      1. mkdir -p src/main/kotlin/com/example/hello
      1. package com.example.hello
      3. import io.ktor.application.*
      4. import io.ktor.http.*
      5. import io.ktor.response.*
      6. import io.ktor.routing.*
      7. import io.ktor.server.engine.*
      8. import io.ktor.server.netty.*
      10. fun main(args: Array<String>) {
      11.    val target = System.getenv("TARGET") ?: "World"
      12.    val port = System.getenv("PORT") ?: "8080"
      13.    embeddedServer(Netty, port.toInt()) {
      14.        routing {
      15.            get("/") {
      16.                call.respondText("Hello $target!\n", ContentType.Text.Html)
      17.            }
      18.        }
      19. }

    3. Switch back to directory

    5. Create a file named Dockerfile and copy the code block below into it.

      1. # Use the official gradle image to create a build artifact.
      2. # https://hub.docker.com/_/gradle
      3. FROM gradle:6.7 as builder
      5. # Copy local code to the container image.
      6. COPY build.gradle .
      7. COPY src ./src
      9. # Build a release artifact.
      10. RUN gradle clean build --no-daemon
      12. # Use the Official OpenJDK image for a lean production stage of our multi-stage build.
      13. # https://hub.docker.com/_/openjdk
      14. # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
      15. FROM openjdk:8-jre-alpine
      17. # Copy the jar to the production image from the builder stage.
      18. COPY --from=builder /home/gradle/build/libs/gradle.jar /helloworld.jar
      20. # Run the web service on container startup.
      21. CMD [ "java", "-jar", "-Djava.security.egd=file:/dev/./urandom", "/helloworld.jar" ]

    6. Create a new file, service.yaml and copy the following service definition into the file. Make sure to replace {username} with your Docker Hub username.

      2. kind: Service
      3. metadata:
      4.   namespace: default
      5. spec:
      6.   template:
      7.     spec:
      8.       containers:
      9.         - image: docker.io/{username}/helloworld-kotlin
      10.           env:
      11.             - name: TARGET
      12.               value: "Kotlin Sample v1"

    Once you have recreated the sample code files (or used the files in the sample folder) you’re ready to build and deploy the sample app.

    1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing {username} with your Docker Hub username:

      1. # Build the container on your local machine
      2. docker build -t {username}/helloworld-kotlin .
      4. # Push the container to docker registry
      5. docker push {username}/helloworld-kotlin

    3. Now that your service is created, Knative will perform the following steps:

      • Create a new immutable revision for this version of the app.
      • Network programming to create a route, ingress, service, and load balance for your app.
      • Automatically scale your pods up and down (including to zero active pods).

    4. To find the URL for your service, use

      1. kubectl get ksvc helloworld-kotlin  --output=custom-columns=NAME:.metadata.name,URL:.status.url
      3. NAME                URL
      4. helloworld-kotlin   http://helloworld-kotlin.default.1.2.3.4.sslip.io

    5. Now you can make a request to your app and see the result. Replace the URL below with the URL returned in the previous command.

      1. curl http://helloworld-kotlin.default.1.2.3.4.sslip.io

    To remove the sample app from your cluster, delete the service record:

    1. kubectl delete --filename service.yaml