Launch your Vaadin-on-Kotlin app quickly in cloud/docker

So you have built your first awesome VoK app - congratulations! You will probably want to launch it outside of your IDE, or even deploy it somewhere on the interwebz. Just pick up any virtual server provider with your favourite Linux distribution.

There are following options to launch your app:

From Gradle, using the Gretty plugin

With proper configuration and build.gradle file, you can simply use the Gretty Gradle plugin to launch wars. Gretty comes pre-configured in the sample quickstarter VoK HelloWorld App, so you can grab the Gradle configuration from there:

git clone
cd vok-helloworld-app
./gradlew web:appRun

You can configure Gretty to launch your app either in Jetty or Tomcat, please read more here: . To launch it in cloud, just ssh to your virtual server, install openjdk 8, git clone your app to the server and run ./gradlew appRun.

From Docker, using the Tomcat image

Really easy - just head to the folder where your my-fat-app-1.0-SNAPSHOT.war file is, and run the following line:

docker run --rm -ti -v "`pwd`:/usr/local/tomcat/webapps" -p 8080:8080 tomcat:9.0.5-jre8

This command will start the Tomcat docker image and will mount your local folder with your war app into Tomcat’s webapps/ folder. Your app will then run at http://localhost:8080/my-fat-app-1.0-SNAPSHOT . To run at http://localhost:8080 just rename your war to ROOT.war. To launch in your virtual server, just copy the WAR into your server, install docker and run the abovementioned command.

You can also create a Tomcat-based Docker image with your app easily. Just drop the following Dockerfile next to your war file:

FROM tomcat:9.0.5-jre8
RUN rm -rf /usr/local/tomcat/webapps/*
COPY *.war /usr/local/tomcat/webapps/ROOT.war
VOLUME /usr/local/tomcat/logs

Then, just run this in the directory with the Dockerfile:

docker build -t my-app .
docker run --rm -ti -p 8080:8080 my-app

Or even better, just use docker-compose.yml:

version: '2'
    build: .
     - "8080:8080"

Then all you need to run is just

docker-compose up --build --force-recreate

(--build will always rebuild the image so that you can play around with the Dockerfile; --force-recreate will delete old containers and create new ones so that Tomcat won’t try to restore sessions from previous run).

Note: the Tomcat docker image now comes with unlimited JCE policy: println("Cipher strength: ${Cipher.getMaxAllowedKeyLength("AES")}") prints Cipher strength: 2147483647

Fat jar

The easiest option is to embed Jetty into your app, then have Jetty launch your app. You can build an uberjar (jar with all dependencies) or a zip file with a start script and a folder with all jars. See the vaadin14-embedded-jetty-gradle project for more details.

Beware though: fat jars may not work for apps that package multiple files into the same location: for example there will be only one MANIFEST.MF. You can read about the pitfalls here: The Fault in Our JARs: Why We Stopped Building Fat JARs.

It is also possible to package Tomcat into the WAR itself, add a launcher class and then simply run it via java -jar your-app.war, thus making an executable WAR. You can read more about this option here: StackOverflow: Embed Tomcat with App in One Fat Jar. Unfortunately I have no experience in this regard.


You can use Docker-Compose to launch both the app and the database in one go. See the vaadin-kotlin-pwa example app documentation for more details.

Written on October 10, 2017