create a Docker image of an application

In my case, I’ll do this with a .jar file (a Java app) (the location of .jar is in the root directory, search: /build/libs/)

You must create a file called “Dockerfile” with the following content:

# Usamos una imagen de Java ligera
FROM eclipse-temurin:21-jdk-alpine

# Directorio de trabajo dentro del contenedor
WORKDIR /app

# Copiamos el jar generado (asegúrate de que el nombre coincida)
COPY ./*.jar app.jar

# Exponemos el puerto de Spring Boot
EXPOSE 7000

# Comando para arrancar la app
ENTRYPOINT ["java", "-jar", "app.jar"]

The EXPOSE 7000 line is for informational purposes only; it does not serve any functional purpose (it’s like a comment)

The COPY command copies the .jar file of the Java app (./*.jar) (the location of .jar) to the destination location (app.jar) (create the output file called app.jar)

create the docker image, with the command (in same location that the file Dockerfile):

docker build -t my-image-name .

You will see something like this:

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View all the images you have:

docker images

Docker manages the images; I don’t know where they are stored

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create a docker container and run it, the docker container has the docker image:

 docker run -d -p 8090:8090 --name my-container-spring mi-app-custom

docker run: It’s 3 commands in 1 single command (docker pull if does not exist locally, docker create, docker start)

the springboot java gradle app runs in the port 8090

I mapped between the host (8090) and the docker container created (8090): -p 8090:8090