Currently there is no official release of Docker available for Ubuntu 18.10. Therefore you’ll run into errors like this one:
$ sudo apt-get install docker-ce
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package docker-ce is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'docker-ce' has no installation candidate
But there is already a way to utilize the test repo to have Docker for Ubuntu 18.10:
sudo apt install apt-transport-https ca-certificates curl software-properties-common
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic test"
sudo apt install docker-ce
Before you apply this fix, please check if the official resources have been updated at: https://docs.docker.com/install/linux/docker-ce/ubuntu/