Deploying a Spring Boot Application in Tomcat in a Docker image

A friend and I are trying to setup a tomcat server in a docker image that will run a .war file that we will supply to it.

We got the Docker image running, this is the Dockerfile:

FROM tomcat:10-jdk8

ADD ./Build/sample.war /usr/local/tomcat/webapps/

EXPOSE 8080

As you can see, it takes the tomcat docker image and adds a our sample.war to the webapps folder. In my eyes, this should be enough to run it.

The Java application is a simple Spring Boot application, this is the main class:

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;

@SpringBootApplication
public class DemoApplication extends SpringBootServletInitializer {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

And this is the Controller we are using:

package com.example.demo.repos;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/")
public class UltraRepository {
    @GetMapping("/test")
    public String testGet() {
        return "Wow, it works!";
    }
}

When I run the application locally, or build the .war file and run it locally on my pc, it works fine. Giving me "Wow, it works" when I go to http://localhost:8080/test.

But when we run it inside a docker file, and go to http://localhost:8080/sample/test (I assume this would be the right url), we get the following message:
https://i.stack.imgur.com/tMQQC.png

While when we look in the logs of the docker which runs tomcat, it says it has started the application successfully.

Does anyone know what we might have to change to get this working?

Thanks in advance!

What is the command that you are using to run the Container ? you need to map your local port to the container port, with -p option, like this: Docker run -p 8080:8080 image_name

You are extending the SpringBootServletInitializer but not overriding its configure method. You can add the following method in a DemoApplication class to fix the issue.

@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
	return application.sources(DemoApplication.class);
}

SpringBootServletInitializer class allows us to configure our application when it's run by the servlet container, by overriding the configure() method.

Turns out this was happening because we used tomcat:10-jdk8, while we had to use tomcat:jdk11, since the SpringBoot application is also made with Java 11.