Compared to VMs we adopted a lot more of a "this is disposable" mindset, we persist any data that must not be destroyed in a failure in an external volume and treat the instance and service as something unreliable, pretty much it's always "Game Day", before deploying something we've already tried to cover the basics of HA (what happens if this service suddenly stops? How is the rest of the system behave? How do we make it automatically restart or reprovision?).

As I said, most of our issues regarded CoreOS (especially running with btrfs, getting out of space for metadata was a pain in the ass for months) but right now, after moving to ext4 + overlayfs we've been running without issues for a combined 28,800 hours of instance time (roughly NO issue in half a month in an environment running 30+ deploys a day).

I've not stated that we're perfect, very far from it, but Docker itself has not been a pain in production. Our private registry is currently running in an Ubuntu-based instance for more than 6 months non-stop (and we push/pull a lot of data from it everyday).

There is nothing particularly magical about Docker that means you can't consider VMs equally as disposable. It's a mindset change about how you build your product, not something inherent to Docker. It's the original concept behind AWS's EC2 - treat your VMs as disposable, and store state elsewhere.