Spring boot Kotlin Auto Build on Docker Compose Runtime

While developing a Spring boot application using Kotlin language with docker, it must go through the new build process to start the server, so when the developer will continuously fix the code, it will automatically receive new code. So in this article will introduce a way to take advantage of an entr tool to listen when the file changes will trigger a rebuild and restart the server. To simulate practically building a RESTful application using Spring boot, Kotlin with Gradle manages dependencies in a Docker environment.

Spring boot

Spring boot helps to create stand-alone based on Spring application that only needs to run with a simple configuration which has the following features:

• Create Spring stand-alone application
• Run Embed Tomcat, Jetty or Undertow directly
• Provide ‘starter’ dependencies to simplify configuration
• Automatically configure Spring and 3rd library at any time
• Provides pre-production features like metrics, health checks and external configuration
• Absolutely no code generation and no XML configuration required

Init project

• Create a new project with Intellij IDEA

• Fill in the information for Spring Artifcat, Gradle, Kotlin, Java: 8

• Select Spring Web dependencies

• Select the directory to save the project

• Wait for it to first build dependencies in build.gradle.kts

• Create a HomeController to test whether the project has run ok yet

Build Dockerfile

In this section, we will use multi-stage to build Dockerfile

Docker image ubuntu:18.04

This section will be the temporary environment to build entr in it should

• package build-essential curl is the basic build-essential curl tool needed.
• curl http://eradman.com/entrproject/code/entr-4.7.tar.gz | tar -xz -C /tmp/ download source and then extract to /tmp directory
• Then go to the directory above to run the command build entr : cd /tmp/entr-4.7 && ./configure && make test && make install after it is done in the /usr/local/bin/entr

Docker image gradle:6.7.1-jdk8

This section plays a role in the project build and listens for file changes

• COPY --from=entr_builder /usr/local/bin/entr /usr/local/bin copy from previous stage to gradle image
• The code below is responsible for stopping the server, deleting the stopped gradle daemons and finally building & restarting the server

• RUN echo 'find . -type f ( -name "*kt" ) | entr -r precompile' > /usr/local/bin/watchfile plays the role of listening for the file change event and calling back to the precompile above.

Build docker-compose.yml

This section describes the services that need to be run in docker

• kt_service is a service containing code that is assigned the work volume of the container to the project directory.
• command: /bin/bash -c 'watchfile' is the command when using docker-compose up will call watchfile written in Dockerfile to listen.

For the first time, need to use the docker-compose up --build command to build images, containers, and volumne from Dockerfile.

After running docker-compose up --build will have the following log:

Certificate that has run successfully.

HomeController test

We’ll try going to the http://localhost:8080 url which will give the output

Next, modify the code from Alive to Die and observe

• In the terminal log there is a line Stop server ... and Start server ... of precompile means it is rebuild and start again with > Task :bootRun

• In the browser, reload the page and it will have output

Conclude

Following the steps described, we do not need to manually type commands such as:

• docker-compose down
• gradle --stop && rm -r /home/gradle/.gradle/daemon && gradle bootRun
• docker-compose up

To make receive changes it has automatically received.

Thank you for reading my article. (bow)

References

• Spring boot
• entr