How to convert a Spring-Boot web service into a Docker image?

Question

I want to access my website from a Docker container but I can\'t. The steps I am trying to implement are as follows. After all the steps I can\'t access the http://loc

Answer 1

To fully address your question (dockerize a Spring Boot project and browse the corresponding webapp in the local browser during, say, development phase), three independent tasks have to be done:

1. Leverage the build of the Docker image by using a Dockerfile that benefits from Docker's cache mechanism (to avoid re-downloading Maven dependencies from scratch every time, and thereby speed-up the build)

2. Make sure the Spring Boot app listens to the specified port for the 0.0.0.0 special IP, not localhost;

3. And finally publish the given port so that you can run for example:

   $ xdg-open http://localhost:8080/index
   

Step 3 is well explained in @Poger's answer, so I'll elaborate a bit more on the steps 1 and 2 only:

1. I have proposed a Dockerfile in this SO thread: How to cache maven dependencies in Docker, inspired by this blog article, that is applicable for Java/Maven projects in general (not only Spring Boot projects):

   # our base build image
   FROM maven:3-jdk-8 as maven
   
   WORKDIR /app
   
   # copy the Project Object Model file
   COPY ./pom.xml ./pom.xml
   
   # fetch all dependencies
   RUN mvn dependency:go-offline -B
   
   # copy your other files
   COPY ./src ./src
   
   # build for release
   # NOTE: my-project-* should be replaced with the proper prefix
   RUN mvn package && cp target/my-project-*.jar app.jar
   
   
   # smaller, final base image
   FROM openjdk:8-jre-alpine
   # OPTIONAL: copy dependencies so the thin jar won't need to re-download them
   # COPY --from=maven /root/.m2 /root/.m2
   
   # set deployment directory
   WORKDIR /app
   
   # copy over the built artifact from the maven image
   COPY --from=maven /app/app.jar ./app.jar
   
   # set the startup command to run your binary
   CMD ["java", "-jar", "/app/app.jar"]
   

   but to refine it further, note that it's recommended to pass an extra system property java.security.egd:

   CMD ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app/app.jar"]
   

   or if you prefer ENTRYPOINT over CMD:

   ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app/app.jar"]
   

2. As mentioned in the SO thread How do I access a spring app running in a docker container?, in the context of a containerized application, localhost should be avoided and replaced with 0.0.0.0 most of the time (namely, if the app should act as a web service replying to incoming requests from outside the container).

   To sum up, you should just try adding the following line in your application.properties file:

   server.address=0.0.0.0