A warm Hello to all the readers!

This is yet another article to understand a new concept of Docker. There is a special file called as Dockerfile.

What is Dockerfile?

Dockerfile is a file that contains instructions to build an image. Instructions are a series of commands that you will otherwise run in running container and then commit it as an image.

Generally dockerfile is kept in a directory that is your current working directory. This directory should contain the files or directories that are to be copied to Docker image when we build it. Though, a dockerfile can reside at any other location as well.

There is defined list of instructions supported by Dockerfile. Following is the entire list.

  • FROM
  • RUN
  • CMD
  • COPY
  • ADD
  • LABEL
  • EXPOSE
  • ENV
  • ENTRYPOINT
  • VOLUME
  • USER
  • WORKDIR
  • ARG
  • ONBUILD
  • STOPSIGNAL
  • HEALTHCHECK
  • SHELL

Example of Dockerfile

Let us write one dockerfile with some routine operations. This will help us to understand meaning of some instructions listed above.

Any dockerfile should begin with FROM instruction. This will initialize our new image from a base image selected with FROM.

FROM ubuntu:bionic

Let us copy one file “hosts” file from current working directory to “/root/hosts” inside Docker.

FROM ubuntu:bionic
COPY hosts /root/hosts

Similar Posts

Docker Concepts

ByH.G.

Hello to all the readers! I am writing down about my learnings on docker. I have learnt docker in the past and used it but never thought to document my learning. I think it is very good to document our own learning of a subject that helps me and maybe you to understand it in…

Docker Image Layers

ByH.G.

Hello to all the readers! Docker image is built in layers. Each instruction that is written in Dockerfile translates into an image layer by the builder. When the image is re-built, builder will re-use layers from earlier builds. If any layer is unchanged, then that layer is picked up from the build cache. However, if…

What is Alpine Image?

ByH.G.

Hello to all the readers! While I was learning Docker, I could see that in most of the places, alpine image of Node.js or Golang is used. Therefore, I went and studied what is an alpine image. The alpine docker image is based on Alpine linux. It is a very small, minimal image with complete…

Using Docker Compose

ByH.G.

Hello to all the readers! I have setup multi container applications separate using docker run commands. But docker offers a nice way to setup multi container apps using Docker compose. Here we define each service in a docker-compose.yml file and then a single command spins up everything for us. The docker-compose.yml for mysql and app…

Error: GraphComment couldn't be load because your settings are invalid. Please visit your admin panel and go to the GraphComment section and enter a valid website URL/ID.