Yes, we do it at Basecamp for all of our legacy apps (and our newest one, HEY), and we've ran Basecamp 2 in production via Kubernetes (we no longer do it, but we did it for a lengthy period of time).
Nothing Kubernetes-related, it was provider-related. We hurriedly moved Basecamp 2 back on-prem after a string of outages caused by our cloud provider at the time. There are a bunch of blog posts on Signal v Noise from early 2019 that talk about it.
Kubernetes for HEY, ECS for the other legacy apps that I mentioned are using Docker, bare metal for Basecamp 2 & 3 (but K8s is on the roadmap for both of them)
