It's been over a year since I wrote my guide on setting up a cheap Chromebook for web development. In that article, I presented three different ways to install a Linux distribution instead of, or sometimes alongside ChromeOS, the native Chromebook operating system. These three methods were all a bit hacky. One required running a heavily sandboxed Android app, while for the other two you had to put the machine in developer mode, which bypasses some of the security measures that make the Chromebook one of the most secure laptops you can find.
Since I wrote that article in September 2017 there's been a new development. Now there is a fourth method of running a native Linux distribution, available to most Chromebook models from the last few years. What makes this new method interesting is that it is an officially supported feature of ChromeOS, so there is no need to activate developer mode, and no need to make concessions on the highly regarded Chromebook security model. This method is based on container technology, and is known by the project name Crostini.