First Docker Image

Create our first Docker Image!

Docker images are further categorized in 2 types

Base Image
If we need to have more control on whats going in my images we should use base image, which means we need to create a Docker image from scratch.
Parent Image
Parent image is something we will be using image created by someone else and build our image on top of this image.

We can write Docker instructions in a file name Dockerfile. Lets see some Dockerfile instructions.

FROM
This must be the fist line in Dockerfile.
MAINTAINER
This is to add the Maintainer in Docker image.
ARG
Build time variables and only available during the creation of Docker image.
ENV
To setup the environment variable in Docker container.
COPY
It takes source and destination locations to copy the file from host machine where we will be building the docker image to docker image.
ADD
It do what COPY does but apart from that it also support the URL’s to get download from external sources. Also it understand the tar formats.
RUN
TO execute command in docker image layer.
CMD
sets default command and/or parameters, which can be overwritten from command line when docker container runs.
ENTRYPOINT
configures a container that will run as an executable.
EXPOSE
To expose the ports on which the application inside the container listening on.
WORKDIR
Its sets up the working directory inside the container.
LABEL
Its a metadata for the container it takes Key Value pair.
VOLUME
It creates a mount point inside the Docker container from the host machine.

sudo debootstrap stretch stretch > /dev/null
sudo tar -C stretch -c . | docker import - stretch

To create a docker image use below command

docker build -t myfirstdockerimage .

or you can specify the Dockerfile path too

docker build -t myfirstdockerimage . -f Dockerfile

To check the running dockers

docker container ls

or

docker ps