How to generate you self signed SSL certificate in 3 Steps for Linux

When Using Reverse Proxy Services Like Cloudflare, you will need to set up your SSL/TLS encryption mode as screenshot shown below.

In this article, we will use the Full mode method. and so we will need to create our self-signed SSL Certificate to be attached to the webserver ie Nginx, or Apache servers, and we can do this in the following 3 steps.
In /etc/opt/ directory you can run.

# openssl req -newkey rsa:2048 -new -nodes -x509 -days 13650 -keyout domain.com.key.pem -out domain.com.cert.pem

replace outputs key and cert files name, then fill the default information of your certificate

Generating a RSA private key
......+++++
.+++++
writing new private key to 'netslovers.com.key.pem'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:Wyoming
Locality Name (eg, city) []:Sheridan
Organization Name (eg, company) [Internet Widgits Pty Ltd]:CompanyName
Organizational Unit Name (eg, section) []:IT
Common Name (e.g. server FQDN or YOUR name) []:domain.com
Email Address []:info@domain.com

and for hardening this SSL Certificate we will generate Diffie-Hellman group dhparam.pem file

# openssl dhparam -out dhparam.pem 4096

That's all, and now we can simply using the output files as our self-signed certificate, for nginx as an example

  ssl on;
  ...................
  ...................
  ssl_certificate      /opt/domain.com.cert.pem;
  ssl_certificate_key  /opt/domain.com.key.pem;
  ssl_dhparam          /opt/dhparam.pem;
  ...................
  ...................