For steps on installing Docker on Ubuntu 18.04, I followed this awesome guide from Digital Ocean. If you'd like to test a Digital Ocean VPS, you can use this $50 promo for 30 days.

Here is the quick and dirty:

Update your existing list of packages:

sudo apt update

Allow apt use packages over HTTPS:

sudo apt install apt-transport-https ca-certificates curl software-properties-common

Add the GPG key for the official Docker repo:

curl -fsSL | sudo apt-key add -

Add the Docker repo sources (this should also work for disco dingo [19.04]):

sudo add-apt-repository "deb [arch=amd64] bionic stable"

Update your list of packages again:

sudo apt update

Install Docker Engine - Community:

sudo apt install docker-ce

Double check that the Docker daemon is running:

sudo systemctl status docker

You should see similar output:

 docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Sun 2019-08-04 03:48:04 UTC; 14h ago
 Main PID: 901 (dockerd)
    Tasks: 15
   CGroup: /system.slice/docker.service
           └─901 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock