"Pin package versions" -- yes. One of the things that has been bugging me about Docker is that if you begin every Dockerfile with an `apt-get -y update`, you never know what you're going to end up with.
On the other hand, pinning every package that you install would end up being pretty verbose.
If you need to pin all your packages then it probably makes more sense to just have your own software package "layer" that imports your pinned base with the packages that are required.
Ubuntu also issues stable release updates (particularly to the latest LTS version) to fix regressions, major bugs, or occasionally update minor release versions. Some applications known to have good release procedures are also allowed updates (eg Firefox).
I hadn't even thought of pinning packages before I read the article; I'm kind of a sucker for apt-get update. I've been thinking a lot about Docker lately, and something in the back of my mind was like, "but what if you don't want the latest version of everything?"
On the other hand, pinning every package that you install would end up being pretty verbose.