Prerequisites

To obtain a Lets Encrypt certificate you must have a public DNS record for your host.

To obtain a Lets Encrypt certificate you must have a public DNS record for your host.

For a production web server this isn't a problem as it will already meet the prerequisites.

For an internal private web server such as those used for running internal infrastructure or an individual developers PC this can be a little tricker.

For a private web server you will still need to create a public DNS A record.

For a private web server we need to do DNS authentication which means that you need to be using a DNS provider from list of DNS providers that Nginx-LE supports.

The simplest way to do this is to acquire the cheapest domain name that you can find. Host the domain name with Cloudflare (host is free for the volumes involved).

For each developer or internal web server create a DNS A record. The IP address you use in the DNS A record does NOT have to be a public IP address. You can just use any private IP address. I would suggest that you don't use any of your real internal ip addresses to avoid exposing information about your internal network.

Now that you have a DNS A record are ready to acquire live certificates.