Docker :3

DevOps Classroom Series – 18/Mar/2021

Docker Image

  • We need to package the applications developed in our organization as docker images Preview
  • Advantages of docker images:
    • Running an app on docker will give more priority to cpu and other resources consumed by application rather than os
    • Cost Reduction: On one host we can run multiple applications seamlessly which reduces hardware costs and os costs
    • Docker is extremely portable, Docker container literally runs anywhere Preview

Installing Docker

  • Lets install Docker on a linux machine
  • We can create a linux vm on any cloud
  • Lets create a ubuntu instance in your cloud
  • For installing docker we will be using the shell script approach which installs the latest version on linux Refer Here
  • Login into the vm
sudo apt update
curl -fsSL https://get.docker.com -o get-docker.sh
sh get-docker.sh
Preview
Preview
  • Exit and relogin and execute the command docker info Preview

First look at building docker images

  • Lets take the lampstack as an example Refer Here
  • First step is to make a note of all the steps required to install/configure your application manually on linux/windows machine
  • Then try to create a Dockerfile which consists of instructions to install/configure your application
  • Dockerfile is a text file which consists of set of Instructions to build a docker image
  • Lets try to make a note of steps to manually create a lamp server on ubuntu server
sudo apt update
sudo apt install apache2 -y
sudo apt install php libapache2-mod-php php-mysql php-cli -y
echo '<?php phpinfo(); ?>' | sudo tee /var/www/html/info.php
  • Basic docker image creation process is
    • choose a base image
    • add your installation/configuration steps
    • create the new image
  • To choose a base image navigate to Refer Here Preview
  • In docker the version of image is referred as tag Refer Here
  • Since our steps are based on ubuntu 18.04 lets choose the tag Preview
  • Lets try to manually check if the image will work or not
  • So lets try to create a container with the ubuntu image and 18.04 tag
docker container run -it <image> /bin/bash
  • In docker convention is <image-name>:<tag> => ubuntu:18.04
docker container run -it ubuntu:18.04 /bin/bash
  • This command creates a ubuntu 18 container and you will be logged in to the container as a root user
  • For commands start using cheatsheet Refer Here
  • In the container we have executed the following steps
apt update
apt install apache2 -y
apt install php libapache2-mod-php php-mysql php-cli -y
echo '<?php phpinfo(); ?>' | tee /var/www/html/info.php
service apache2 start
  • The way to write Dockerfile contents
FROM ubuntu:18.04
RUN apt update 
RUN apt install apache2 -y
RUN apt install php libapache2-mod-php php-mysql php-cli -y
RUN echo '<?php phpinfo(); ?>' | tee /var/www/html/info.php
RUN service apache2 start
EXPOSE 80