I am going to say the thing that Kubernetes evangelists will not: K8s is overkill for most Rails applications. If you have one app, a few background workers, and a Postgres database, Kamal or ECS or even a well-configured VPS will serve you fine. Kubernetes solves problems at a scale that most Rails teams never reach, and it introduces operational complexity that can consume entire engineering teams.
There, I said it. Now here is why you should learn it anyway.
Understanding Kubernetes teaches you distributed systems concepts that transfer everywhere. Pods are processes. Services are load balancers. ConfigMaps are environment management. Deployments are rollout strategies. Health checks, resource limits, horizontal autoscaling -- these are not Kubernetes ideas, they are infrastructure ideas that Kubernetes happens to formalize beautifully. Learning K8s makes you understand networking, DNS, storage, and deployment at a level that Kamal or Heroku actively hide from you.
Kelsey Hightower's talks will make you want to Kubernetes everything. His enthusiasm is infectious and his explanations are brilliant. Resist the urge to migrate your side project to K8s. Watch the talks, absorb the mental models, and deploy to K8s only when the scale demands it or the job requires it.
The YAML wall is real and it is demoralizing. You will write more YAML than Ruby for a few weeks. You will misindent something and spend an hour debugging why your pod will not start. You will question your life choices. Then it clicks, and you start to see the YAML as declarative infrastructure -- you tell Kubernetes what you want, and it figures out how to get there. Helm and Kustomize exist to manage the YAML sprawl. Use them.
If a job posting says "Kubernetes experience," this module is why they are asking. Not because they expect you to administer the cluster, but because they want engineers who understand the platform their code runs on.