Kotlin is a JVM-compatible language that has gained popularity in recent years for its concise syntax and interoperability with Java. Docker is a containerization platform that enables developers to package and run applications in isolated environments.
In this article, we will show how to package a Kotlin application into a Docker container and run it on a server. We will also briefly discuss some of the benefits of using Kotlin and Docker together.
To package a Kotlin application in a Docker container, we need to create a Dockerfile
that specifies the base image and the necessary dependencies. We will use the openjdk:8-jdk-alpine
image as our base image. This image contains the OpenJDK 8 JVM and the Alpine Linux distribution. Alpine Linux is a lightweight Linux distribution that is ideal for Docker containers.
We will also need to specify the kotlin-stdlib
dependency. This dependency contains the Kotlin standard library, which is required for all Kotlin applications.
FROM openjdk:8-jdk-alpine
# Add the Kotlin standard library as a dependency
RUN apk add --no-cache kotlin-stdlib
Next, we need to copy our Kotlin code into the container. We will place our code in the /app
directory.
# Copy our Kotlin code into the container
COPY src/ /app/src/
Finally, we need to specify the ENTRYPOINT
and CMD
values. The ENTRYPOINT
value specifies the command that will be run when the container is started. The CMD
value specifies the arguments that will be passed to the ENTRYPOINT
command. In our case, we will use the kotlinc
command to compile our code and the java
command to run our compiled code.
# Specify the entrypoint and command
ENTRYPOINT ["kotlinc", "-include-runtime", "/app/src/main.kt", "-d", "/app/app.jar"]
CMD ["java", "-jar", "/app/app.jar"]
The -include-runtime
argument tells the kotlinc
compiler to include the Kotlin runtime in the compiled code. This is necessary because the Kotlin runtime is not included in the kotlin-stdlib
dependency.
Now that we have our Dockerfile
, we can build our Docker image and run our Kotlin application in a Docker container.
First, we need to build our Docker image. We will use the docker build
command to build our image. We will name our image kotlin-app
and tag it with the latest
tag.
$ docker build -t kotlin-app:latest .
Next, we need to run our Docker image. We will use the docker run
command to run our image. We will also specify the -p 8080:8080
argument, which will map port 8080
on the host to port 8080
in the container.
$ docker run -p 8080:8080 kotlin-app:latest
Our Kotlin application is now running in a Docker container and can be accessed at http://localhost:8080
.
There are several benefits to using Kotlin and Docker together.
First, Kotlin is a very concise language. This means that our Kotlin code will be much smaller than the equivalent Java code. This is important when packaging applications in Docker containers because smaller images are faster to build and deploy.
Second, Kotlin is fully interoperable with Java. This means that we can easily use existing Java libraries in our Kotlin code. This is important when containerizing existing Java applications with Docker.
Third, Kotlin is a JVM-compatible language. This means that we can run our Kotlin code on any platform that supports the JVM. This is important when deploying applications in Docker containers because we can run our containers on any platform that supports Docker, regardless of the underlying operating system.
In this article, we showed how to package a Kotlin application in a Docker container and run it on a server. We also briefly discussed some of the benefits of using Kotlin and Docker together.