A simple web app written in Kotlin using Ktor that you can
use for testing. It reads in an env variable TARGET
and prints "Hello
${TARGET}". If TARGET is not specified, it will use "World" as the TARGET.
- A Kubernetes cluster with Knative installed. Follow the installation instructions if you need to create one.
- Docker installed and running on your local machine, and a Docker Hub account configured (we'll use it for a container registry).
While you can clone all of the code from this directory, hello world apps are generally more useful if you build them step-by-step. The following instructions recreate the source files from this folder.
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Create a new directory and cd into it:
mkdir hello cd hello
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Create a file named
Main.kt
atsrc/main/kotlin/com/example/hello
and copy the code block below into it:mkdir -p src/main/kotlin/com/example/hello
package com.example.hello import io.ktor.application.* import io.ktor.http.* import io.ktor.response.* import io.ktor.routing.* import io.ktor.server.engine.* import io.ktor.server.netty.* fun main(args: Array<String>) { val target = System.getenv("TARGET") ?: "World" val port = System.getenv("PORT") ?: "8080" embeddedServer(Netty, port.toInt()) { routing { get("/") { call.respondText("Hello $target", ContentType.Text.Html) } } }.start(wait = true) }
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Switch back to
hello
directory -
Create a new file,
build.gradle
and copy the following settingbuildscript { ext.kotlin_version = '1.2.61' ext.ktor_version = '0.9.4' repositories { mavenCentral() } dependencies { classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" } } apply plugin: 'java' apply plugin: 'kotlin' apply plugin: 'application' sourceCompatibility = 1.8 compileKotlin { kotlinOptions.jvmTarget = "1.8" } compileTestKotlin { kotlinOptions.jvmTarget = "1.8" } repositories { jcenter() maven { url "https://dl.bintray.com/kotlin/ktor" } } mainClassName = 'com.example.hello.MainKt' jar { manifest { attributes 'Main-Class': mainClassName } from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } } } dependencies { compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version" compile "io.ktor:ktor-server-netty:$ktor_version" testCompile group: 'junit', name: 'junit', version: '4.12' }
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Create a file named
Dockerfile
and copy the code block below into it.# Use the official gradle image to create a build artifact. # https://hub.docker.com/_/gradle FROM gradle as builder # Copy local code to the container image. COPY build.gradle . COPY src ./src # Build a release artifact. RUN gradle clean build --no-daemon # Use the Official OpenJDK image for a lean production stage of our multi-stage build. # https://hub.docker.com/_/openjdk # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds FROM openjdk:8-jre-alpine # Copy the jar to the production image from the builder stage. COPY --from=builder /home/gradle/build/libs/gradle.jar /helloworld.jar # Service must listen to $PORT environment variable. # This default value facilitates local development. ENV PORT 8080 # Run the web service on container startup. CMD [ "java", "-jar", "-Djava.security.egd=file:/dev/./urandom", "/helloworld.jar" ]
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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.apiVersion: serving.knative.dev/v1alpha1 kind: Service metadata: name: helloworld-kotlin namespace: default spec: runLatest: configuration: revisionTemplate: spec: container: image: docker.io/{username}/helloworld-kotlin env: - name: TARGET 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.
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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:# Build the container on your local machine docker build -t {username}/helloworld-kotlin . # Push the container to docker registry docker push {username}/helloworld-kotlin
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After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. Ensure that the container image value in
service.yaml
matches the container you built in the previous step. Apply the configuration usingkubectl
:kubectl apply --filename service.yaml
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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).
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To find the IP address for your service, use
kubectl get service knative-ingressgateway --namespace istio-system
to get the ingress IP for your cluster. If your cluster is new, it may take sometime for the service to get assigned an external IP address.kubectl get service knative-ingressgateway --namespace istio-system
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE knative-ingressgateway LoadBalancer 10.23.247.74 35.203.155.229 80:32380/TCP,443:32390/TCP,32400:32400/TCP 2d
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To find the URL for your service, use
kubectl get ksvc helloworld-kotlin --output=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain
NAME DOMAIN helloworld-kotlin helloworld-kotlin.default.example.com
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Now you can make a request to your app to see the result. Replace
{IP_ADDRESS}
with the address you see returned in the previous step.curl -H "Host: helloworld-kotlin.default.example.com" http://{IP_ADDRESS}
Hello Kotlin Sample v1
To remove the sample app from your cluster, delete the service record:
kubectl delete --filename service.yaml