functions

Using Kotlin with Google Cloud Functions

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Deploying Kotlin Cloud Function

When deploying to Google Cloud Functions, you can deploy functions for HTTP triggers or for PubSub messages.

Http Trigger

An example function for HTTP triggers resides in src/main/kotlin/HttpExample.kt. Deploy it with the following gcloud command:

gcloud functions deploy http-example \
    --runtime=java8 \
    --entry-point=HttpExample.helloWorld \
    --trigger-http \
    --source=.

The dependencies are built automatically using pom.xml. If you'd like to use Gradle instead, see Deploy a JAR below.

Now you can make a request to the returned URL to see the "Hello World" response:

$ curl "https://[YOUR_ZONE]-[YOUR_PROJECT_ID].cloudfunctions.net/http-example"
Hello, World!

You can see the URL for your function by running the following:

gcloud functions describe http-example | grep url

Where "jar-example" is the name of your Cloud Function.

Pub/Sub Trigger

An example function for Pub/Sub resides in src/main/kotlin/EventExample.kt. Before you deploy it, you need to create a Pub/Sub topic. This example uses hello-topic:

gcloud pubsub topics create hello-topic

Now deploy the Cloud Function with the following gcloud command:

gcloud functions deploy pubsub-example \
    --runtime java8 \
    --entry-point EventExample.helloPubSub \
    --trigger-resource hello-topic \
    --trigger-event google.pubsub.topic.publish

Now you can trigger a call to the pubsub-example function and pass in base64-encoded data. The data below says "Hello, Pub/Sub!"

gcloud functions call pubsub-example --data '{"data":"SGVsbG8sIFB1Yi9TdWIh"}'

Now if you open the Stackdriver Logging UI, or call the gcloud functions logs read command, you will see the output:

$ gcloud functions logs read pubsub-example
NAME            EXECUTION_ID  TIME_UTC                 LOG
pubsub-example  wss5cki38tkb  2019-05-08 21:24:28.061  INFO: Hello, Pub/Sub!

Deploy a JAR (required for building with Gradle)

Google Cloud Functions support deploying pre-built fat JARs. This is especially useful when building functions with Gradle, as Cloud Functions does not currently support building from Gradle automatically. A fat JAR is built automatically using the shadowJar task when you run gradle build:

apply plugin: 'com.github.johnrengelman.shadow'
tasks.build.dependsOn tasks.shadowJar

Now you can build a fat JAR file:

./gradlew build

To deploy the JAR, it must be in directory by itself:

mkdir jar-deployment
cp build/libs/functions-all.jar jar-deployment/

Now you can deploy to Google Cloud Functions by providing the directory your JAR resides in as the source:

gcloud functions deploy jar-example \
    --runtime=java8 \
    --entry-point=HttpExample.helloWorld \
    --trigger-http \
    --source=jar-deployment/