I've investigated it a few times for several Rails applications that I maintain, but I've never completed a rollout. Running Rails on Docker isn't a huge hurdle, but Capistrano's default git-based deploys are just so _easy and fast_ once the server is set up. I also have to balance deploying Docker with ops' expertise.
I do recommend getting a copy of _Docker for Rails Developers_ to avoid needing to read a bunch of disparate blogs, though it covers Docker Swarm instead of Kubernetes.
Fresh book recommendations delivered straight to your inbox every Thursday.