Letsencrypt is an initative which aims to increase the use of encryption for websites. It basically allows people to apply for free certificates provided that they prove the they control the requested domain. We will look at the what is needed to secure your MongoDB installation. For more details on setting up a MongoDB server see MongoDB 3.2.x.
We sould to set the hostname to match the name of the certificate we are going to optain.
sudo hostname mongo0.example.com
Then update the hostname file to set the server name permanently.