How to create a Dockerfile?

A Docker file is usually created in the base directory of your project and named as a plain text file “Dockerfile”. In this Dockerfile, a series of commands are written to build a new Docker image.

Here’s a basic structure on how to create a Dockerfile.

1. Create a file and name it Dockerfile.

1. Open this Dockerfile in any text editor you prefer.

1. Each Docker file begins with defining a base image with the ‘FROM’ keyword. For instance,

`FROM ubuntu:18.04` This line will be pulling a base image of Ubuntu 18.04 from Docker Hub.

1. Use ‘RUN’ command to run operations or install any applications. For instance,

`RUN apt-get update` This line will run update in Ubuntu.

1. The ‘COPY’ command is used to copy files or directories from the host machine to the Docker container. For example,

`COPY . /app` This line will copy everything from the current directory to /app directory in the container .

1. The ‘WORKDIR’ keyword is used to specify a working directory in which the command defined with ‘CMD’ keyword will be ran. For example,

`WORKDIR /app` This sets the working directory inside the container to /app.

1. The ‘CMD’ keyword is used to provide defaults that can be executed as an executable or can be ignored in case a user specifies arguments while running the Docker image. For example,

`CMD [“index.js”]` When you’ll run the Docker image, it will execute index.js file.

1. The ‘EXPOSE’ keyword is used to allow interaction between the container and the outside world. For example,

`EXPOSE 80` This line will expose port 80 of the Docker container.

Remember, each instruction creates a new layer in the image, so try to minimize the number of instructions to have lightweight Docker images.

Below is the final version of example Dockerfile.

``` FROM ubuntu:18.04

RUN apt-get update COPY . /app WORKDIR /app CMD [“index.js”] EXPOSE 80 ```

This file is very simple and does not include many specifics, but Dockerfile can get complex based on your application requirements. You can build the Docker image based on this Dockerfile using `docker build` command.