Apple official website says:

macOS Server is changing to focus more on management of computers, devices, and storage on your network. As a result, some changes are coming in how Server works. A number of services will be deprecated, and will be hidden on new installations of an update to macOS Server coming in spring 2018. If you’ve already configured one of these services, you’ll still be able to use it in the spring 2018 macOS Server update.

That means:

Many services macOS Server we like are going awaiy. Actually Apple started hiding them under the menu already.

What is going away?

Cupertino plans to stop supporting DHCP, DNS, mail, messages, NetInstall, VPN, the Web server, the Wiki, as well as calendar and contact support.

Learn more:

• Todd Olthoff YouTube channel
• Apple website