Ubuntu Server 18.04 Minimal OS Install
Minimal Ubuntu Server images are designed for automated deployment at scale. They use the optimised kernels and optimised boot process on their target compute substrate. These images have a greatly reduced default package set, without many convenience tools for interactive usage. They are much smaller, boot faster, and will require fewer security updates over time since they have fewer packages installed.
Minimal instances are not intended to be comfortable to use at the command line, but you can apt-get and snap install anything as usual, so on the occasions when humans do need to use them for debugging purposes, they can be made comfortable. The 'unminimize' command will install the standard Ubuntu Server packages if you want to convert a Minimal instance to a standard Server environment for interactive use.
Since they retain full support for installing from the Ubuntu archive, Minimal Ubuntu has access to the same breadth of software, and the same excellent security maintenance, as the regular server images. Combined with full snap support, anything you can do with the regular Ubuntu images, you can do with the minimal images.
Minimal Server support is from How to Setup Ubuntu Minimal Server on Azure