just as I decided to install Docker, it somehow stopped being available.

The Amazon CloudFront distribution is configured to block access from your country.

Installed Docker on the laptop.

Had been afraid of it locally for a long time — figured it would eat up all the space and thrash the SSD.

But eventually had to bite the bullet. Moved /var/lib/docker via a symlink to the HDD, will keep an eye on the space usage.