Running a Tomcat-based Spring Boot application in Docker

In one of the projects I am working on, I was tasked from taking a Tomcat application that ran on an EC2 server, and get it running with the Spring Boot framework in a Docker container. The twist is that the application needed read-write access to the resources folder within the project. In order to do that, the application needed to be run as an "exploded" WAR file (It had been run that way on the old server as well).

I accomplished this with this Docker file:

	FROM openjdk:8-alpine
	ENV TZ America/New_York
	RUN ln -snf /usr/share/zoneinfo/${TZ} /etc/localtime
	RUN echo "${TZ}" > /etc/timezone
	# Declare the working directory
	WORKDIR /microservice
	# Copy and explode the WAR to the working directory
	COPY my-application/target/*-exec.war /microservice.war
	RUN jar xvf /microservice.war
	RUN rm /microservice.war
	# RUN the microservice
	ENTRYPOINT ["java", "org.springframework.boot.loader.WarLauncher"]

view raw microservice.docker hosted with ❤ by GitHub

The WAR file is compiled with the "spring-boot-maven-plugin", and includes all the dependency JARs, so the application can be run stand-alone.

That entry in the POM is:

	...
	<packaging>war</packaging>
	...
	<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-tomcat</artifactId>
	</dependency>
	...
	<plugin>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-maven-plugin</artifactId>
	<configuration>
	<classifier>exec</classifier>
	</configuration>
	</plugin>
	...

view raw pom.xml hosted with ❤ by GitHub

And the "org.springframework.boot.loader.WarLauncher" Class is what Spring Boot uses to bootstrap the applicatiton on the embedded Tomcat.