I fail to see how they are in any way comparable. MySQL and Mongo both have made a lot of money selling into the enterprise with the decades old per server licensing model. Now Mongo is starting to make inroads into the data warehouse space with their partnerships with Teradata, SAP etc. They aren't selling a PaaS or web application that will just be used by a development team here and there.

Docker seems to be much closer to Atlassian. Which could well be their biggest competitor one day.

Though Docker's current valuation wasn't disclosed, it was rumored at $400m for the Series C round, and has probably at least doubled since then, given the amount of capital raised right now and the fact that they haven't spent all of the Series B. I seriously doubt that a $1bn exit would make Docker's investors happy

MySQL was installed at virtually every hosting provider and was 1/4 of the stack for a massive number of developers. I'm not even sure what Docker does.