Make SSL with Let's Encrypt for Spring-Boot application running with Nginx

Let's Encrypt provides free certificate for transport layer security encryption. It is possible to generate the certificate for different web servers.

In this case it was a spring-boot application that was running with Nginx. Following are the setps to generate and install the SSL:

Setp 1: 
First of all install the certbot FOR Nginx using the following commands: 
$ sudo apt-get update
$ sudo apt-get install software-properties-common
$ sudo add-apt-repository ppa:certbot/certbot
$ sudo apt-get update
$ sudo apt-get install python-certbot-nginx

Step 2:  
We need to ensure that the domain name exists in Nginx configuraiton file like below:

 server {
     server_name <your domain>;
     ....
 }

Step 3:  
Once the certbot is installed things are ready to generate the certificate. The following command is used to generate the certificate for Nginx:  

sudo certbot --nginx -d <your domain>

Step 4:  
Once we run the above command it will automatically install the certificate in Nginx configuration file like below:

listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/<your-domain>/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/<your-domain>/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

if ($scheme != "https") {
    return 301 https://$host$request_uri;
} # managed by Certbot

NB: In this step it will ask for the confirmation about force https. If we want to force https then it will generate the last 3 lines

Step 5:
In our case the sprint-boot application was running at port 8080. So we had to add a proxy_pass to run the spring-boot with Nginx like below:

location / {     proxy_pass http://localhost:8080;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    # First attempt to serve request as file, then
    # as directory, then fall back to displaying a 404.
    # try_files $uri $uri/ =404;
    # Uncomment to enable naxsi on this location
    # include /etc/nginx/naxsi.rules
}

Following situation might occur whlie generating the SSL certificate for nginx.

Performing the following challenges:
Client with the currently selected authenticator does not support any combination of challenges that will satisfy the CA.

To solve the issue run the following command:
Solution:
sudo certbot --authenticator standalone --installer nginx -d <your-domain> --pre-hook "service nginx stop" --post-hook "service nginx start"