(June 2018)
Docker provides good installation instructions.
On Debian, this boils down to:
apt-get remove docker docker-engine docker.ioapt-get install apt-transport-https ca-certificates curl gnupg2 software-properties-commoncurl -fsSL https://download.docker.com/linux/debian/gpg | sudo apt-key add -add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/debian $(lsb_release -cs) stable"apt-get updateapt-get install docker-cedocker run hello-world$ docker run -d -p 8080:80 nextcloud