ubuntu : auto restart application as a service after server reboot

You can simply use "nohup java -jar yourappname.jar &" to run an application at backend , but how to automatically start this application as a service after server reboot ?

aws : free ssl cert with let's encrypt

Let’s Encrypt (LE) is a free, automated, and open certificate authority (CA) so that we do not need to pay a cent for a SSL certificate.