A Docker Image is created by the sequence of commands written in a file called as Dockerfile. In other word you can say Docker images are templets used to create Docker container. While container is a running instance of images

                       FROM openjdk:8

                       ADD target/hello-server.jar hello-server.jar

                       EXPOSE 8080

                       ENTRYPOINT ["java", "-jar", "hello-server.jar"]

save file with name as Dockerfile

Then run the below docker build command for create images

       docker build -f Dockerfile -t hello-server .
   
      Here **-f** is used for Name of the Dockerfile (Default is Path/Dockerfile ) and **Dockerfile**  is docker file
      -t is used tag list (Name and optionally a tag in the 'name:tag')

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Command for create Dockerfile

ADD – Defines files to copy from the Host file system onto the Container

            ADD ./local/config.file    /etc/service/config.file

CMD – This is the command that will run when the Container starts

     CMD ["nginx", "-g", "daemon off;"]

ENTRYPOINT – Sets the default application used every time a Container is created from the Image. If used in conjunction with CMD, you can remove the application and just define the arguments there

     CMD Hello World!

     ENTRYPOINT echo

ENV – Set/modify the environment variables within Containers created from the Image.

   ENV VERSION 1.0

EXPOSE – Define which Container ports to expose

 EXPOSE 80

FROM – Select the base image to build the new image on top of

 FROM ubuntu:latest

LABEL maintainer – Optional field to let you identify yourself as the maintainer of this image. This is just a label (it used to be a dedicated Docker directive).

   LABEL maintainer="[email protected]"

RUN – Specify commands to make changes to your Image and subsequently the Containers started from this Image. This includes updating packages, installing software, adding users, creating an initial database, setting up certificates, etc. These are the commands you would run at the command line to install and configure your application

   RUN apt-get update && apt-get upgrade -y && apt-get install -y nginx && rm -rf /var/lib/apt/lists/*

USER – Define the default User all commands will be run as within any Container created from your Image. It can be either a UID or username

  USER docker

VOLUME – Creates a mount point within the Container linking it back to file systems accessible by the Docker Host. New Volumes get populated with the pre-existing contents of the specified location in the image. It is specially relevant to mention is that defining Volumes in a Dockerfile can lead to issues. Volumes should be managed with docker-compose or “docker run” commands.

  VOLUME /var/log

WORKDIR – Define the default working directory for the command defined in the “ENTRYPOINT” or “CMD” instructions

  WORKDIR /home