Create a Server for Devloper1
Install git on it

Go to Git hub and create a repository with readme file added

there will be a defualt main branch

Create 3 more branches Dev, QA, Prod

Make Dev branch as defualt branch

Go to Settings--> Branches--> click on switch to other branches--> select dev in drop down and click on update

Now dev is default branch

And delete main branch

go to local machine of Developer and Clone the git hub repository

Dev branch must be there.

Create a new file with index1.html and save it
  
<h1> this my app </h1>
<h1> created by Sonal</h1>

Add file to local repo and push the code to Remote repo under dev branch

# git add .
# git commit -m "added index1.html"
# git push origin Dev

Check in github under Dev do we have the file

Now Build and Deploy the code using Jenkins & Docker

Go to jenkins--> DeployDev Job
give the new repo name and branch name as Dev

under build give this script

rm -rf mydockerfile
mkdir mydockerfile
cd mydockerfile
cp /var/lib/jenkins/workspace/DeployDev/index1.html .
touch dockerfile
cat <<EOT>> dockerfile
FROM ubuntu
RUN apt-get update
RUN apt-get install nginx -y
COPY index1.html /var/www/html
EXPOSE 80
CMD ["nginx","-g","daemon off;"]
EOT
sudo docker build -t myimage:$BUILD_NUMBER .
sudo docker run -itd -P myimage:$BUILD_NUMBER


Code will be deployed at URL : http://3.143.147.140:32776/index1.html


********************************************

Now go to Git hub and create pull request to merge code with QA branch

Now Build and Deploy the code using Jenkins & Docker

Go to jenkins--> DeployQA Job
give the new repo name and branch name as QA

under build give this script

rm -rf mydockerfile
mkdir mydockerfile
cd mydockerfile
cp /var/lib/jenkins/workspace/DeployQA/index1.html .
touch dockerfile
cat <<EOT>> dockerfile
FROM ubuntu
RUN apt-get update
RUN apt-get install nginx -y
COPY index1.html /var/www/html
EXPOSE 80
CMD ["nginx","-g","daemon off;"]
EOT
sudo docker build -t myimage:$BUILD_NUMBER .
sudo docker run -itd -P myimage:$BUILD_NUMBER


Code will be deployed at URL : http://3.143.147.140:32776/index1.html


As there will be defects , go to local repo and make chnages to index1.html for defect fix as part of QA

Push the code to Dev branch first

Build and Deploy in DEV Server

Now merge DEV code to QA branch in deploy in QA

*************************************

Once everything is tested in QA, 

Create a pull request to merge QA branch to Prod branch


Now Build and Deploy the code using Jenkins & Docker

Go to jenkins--> DeployProd Job
give the new repo name and branch name as Prod

under build give this script

rm -rf mydockerfile
mkdir mydockerfile
cd mydockerfile
cp /var/lib/jenkins/workspace/DeployProd/index1.html .
touch dockerfile
cat <<EOT>> dockerfile
FROM ubuntu
RUN apt-get update
RUN apt-get install nginx -y
COPY index1.html /var/www/html
EXPOSE 80
CMD ["nginx","-g","daemon off;"]
EOT
sudo docker build -t myimage:$BUILD_NUMBER .
sudo docker run -itd -P myimage:$BUILD_NUMBER


Code will be deployed at URL : http://3.143.147.140:32776/index1.html