Solving my fun, frustrating docker-machine error

from blog ntietz.com blog, | ↗ original
Last Saturday, I ran into a problem doing a routine backup of a web app I maintain. In fact, this was the second time I ran into the exact same issue, so it's time to write it down. (Hopefully, the third time I run into this, I have the presence of mind to look up my own solution!) My web app is deployed using docker-machine and docker-compose....