Unable to load Spring Boot application running in Docker

Question

I have created a simple Spring Boot v2.1.10 application with Gradle v5.6.4 and trying to run it in Docker v18.09.9, build 1752eb3.The application is working locally, but when I run it in Docker, the webpage doesn't load in the browser. Though, it is starting in the Docker console properly without any error.

Dockerfile content

FROM java:8
EXPOSE 9090:8181
ADD /build/libs/docker-app-0.0.1-SNAPSHOT.jar docker-app-0.0.1-SNAPSHOT.jar
ENTRYPOINT ["java","-jar","docker-app-0.0.1-SNAPSHOT.jar"]

Springboot app controller

@RestController
public class Resource {

    @GetMapping(value = "/home")
    public String home() {
        return "<h1>up!!!.....running from docker!!!</h1>";
    }
}

Docker run command :~/java-project/docker-app$ sudo docker run -p 9090:8181 springboot

Docker console output

:~/java-project/docker-app$ sudo docker run -p 9090:8181 springboot

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::       (v2.1.10.RELEASE)

2019-11-19 20:38:03.870  INFO 1 --- [           main] com.DockerAppApplication                 : Starting DockerAppApplication on 93febc16ff7d with PID 1 (/docker-app-0.0.1-SNAPSHOT.jar started by root in /)
2019-11-19 20:38:03.877  INFO 1 --- [           main] com.DockerAppApplication                 : No active profile set, falling back to default profiles: default
2019-11-19 20:38:06.459  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 9090 (http)
2019-11-19 20:38:06.528  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-11-19 20:38:06.528  INFO 1 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.27]
2019-11-19 20:38:06.669  INFO 1 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-11-19 20:38:06.669  INFO 1 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 2642 ms
2019-11-19 20:38:07.012  INFO 1 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-11-19 20:38:07.333  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 9090 (http) with context path ''
2019-11-19 20:38:07.339  INFO 1 --- [           main] com.DockerAppApplication                 : Started DockerAppApplication in 4.276 seconds (JVM running for 5.029)

NOTE: When I give the same port number( sudo docker run -p 9090:9090 springboot ) in run command and in Dockerfile, then it's working properly.

What's different in case of different port numbers in the docker run command?

Answer 1

TL;DR

Change your mapping to -p 8181:9090

---

You got that the wrong way. The -p 9090:8181 setting will expose the container's port 8181 on the host's port 9090 — assuming that port is not in use. You can effectively use the port 9090 on the host, but the Spring Boot application in the container is not listening on 8181 , so you won't get any response back from it.

When you do -p 9090:9090 you are correctly exposing 9090 on the host and the container; again, the Spring Boot application is effectively listening on port 9090 , so you are able hit the Spring Boot application and get something back.

In any case, what you are looking for is -p 8181:9090 . That will let you use the application on port 8181 in the browser/host, while the Spring Boot application uses 9090 .