Why I increasingly think we're unlikely to ever use Docker
Apart from my general qualms about containers in our environment, I have increasingly wound up thinking that Docker itself is not a good fit for our environment even if we want to use some form of service containerization for various reasons. The problem is access to data.
Our current solution for services gaining access to service data is NFS filesystems from our central fileservers. Master DNS zone files, web pages and web apps for our administrative web server, core data files used by our mail gateway, you name it and it lives in a NFS filesystem. As far as I can tell from reading about Docker, this is rather against the Docker way. Instead, Docker seems to want you to wrap your persistent data up inside Docker data volumes.
It's my opinion that Docker data volumes would be a terrible option for us. They'd add an extra level of indirection for our data in one way or another and it's not clear how they allow access from different Docker hosts (if they do so at all). Making changes and so on would get more difficult, and we make changes (sometimes automated ones) on a frequent basis. In theory maybe we could use (or abuse) Docker features to either import 'local' filesystems (that are actually NFS mounts) into the containers or have the containers do NFS mounts inside themselves. In practice this clearly seems to be swimming upstream against the Docker current.
It's my strong view that much software has ways that it expects to be used and ways that it doesn't expect to be used. Even if you can make software work in a situation it doesn't expect, it's generally not a good idea to do so; you're almost always buying yourself a whole bunch of future pain and heartburn if you go against what the software wants. The reality is that the software is not a good fit for your situation.
So: Docker does not appear to be a good fit for how we operate and as a result I don't think it's a good choice for us.
(In general the containerization stories I read seem to use some sort of core object store or key store as their source of truth and storage. Pushing things to Amazon's S3 is popular, for example. I'm not sure I've seen a 'containerization in a world of NFS' story.)