This quick tutorial is assuming you already have a working installation of Let's Encrypt certificates in your site. We will go through the configuration of Nginx and your Spring Boot 2 application. If you need help to get the certificates working you can follow this guide or in Let's Encrypt documentation
The first step will be to export your let's encrypt certificate to a suitable format and location.
Spring Boot expects PKCS12. We need to create a keystore. Doing that you will be asked to provide a password. This password needs to be provided to your Spring application as well (Find a secure way to do it. We are using application properties in this example for simplicity). The value under -name will be the alias of this key in the keystore.
So let's go hands on...