Dockerfile

 

DOCKERFILE (on top of docker image, there is an instruction layer)

A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build users can create an automated build that executes several command-line instructions in succession.

vi Dockerfile (no extensions)

FROM ubuntu #downloading base

ARG DEBIAN_FRONTEND=noninteractive 

#noninteractive for automation so it does not ask geographical bla bla bla..

RUN apt-get update 

#run is adding instruction on the instruction layer

RUN apt-get -y install apache2

ADD . /var/www/html 

#add is copy the file from host machine to docker image folder

ENTRYPOINT apachectl -D FOREGROUND 

#entrypoint whenever docker image is used in a container, some commands need to be executed automatically

ENV name DEVOPS 

#environment variable is used on the global level






BUILD THE DOCKERFILE

docker build . -t webimg

when doing this, docker will create an intermediate container to try each steps. after each steps, it will destroy the intermediate container and go to next step, then create an intermediate container again.

run the build image in a container:

docker container run --name webserver -dit -p 80:80 prod/webimg

from here you can do the following:

A) check if FROM ubuntu is confirmed:
go into the container:
    docker exec -it webserver bash
then run this command:
    uname -a
(this will confirm the ubuntu)

B) check if RUN is confimed:
in container, type:
    service apache2 status

C) check if ADD . is confirmed:
in container, type:
    ls /var/www/html/

D) check if ENV name DEVOPS is confimed:
in container, type:
    env