Dockerfile

A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image

The Docker build command executes the Dockerfile and builds a Docker image from it.

 A Docker image typically consists of:

• A base Docker image on top of which to build your own Docker image.
• A set of tools and applications to be installed in the Docker image.
• A set of files to be copied into the Docker image (e.g configuration files).
• Possibly a network (TCP / UDP) port (or more) to be opened for traffic in the firewall..etc

Dockerfile Structure

A Dockerfile consists of a set of instructions. Each instruction consists of a command followed by arguments to that command, similar to command line executables. 

Here is a simple example of a Dockerfile:

# The base image

FROM ubuntu:latest

# More instructions here that install software and copy files into the image.

COPY    /myapp/target/myapp.jar    /myapp/sriniapp.jar

# The command executed when running a Docker container based on this image.

CMD echo Starting Docker Container

Refer: https://www.youtube.com/watch?v=QLENvSMSD-0