If you need stateful files in a microservice, just mount a network filesystem. Yes, it's slow. Yes, it's buggy. Yes, it's not very portable. Yes, there are locking issues. But if you really need stateful files in a microservice, something is already fucked up. Network filesystems are a simple and cheap way to add that functionality and more. You get 'infinite' storage, redundancy, persistence, shared volumes, intra-cluster data availability, centralized data lifecycle management, etc, and no need for more custom Kubernetes logic just to persist some files. It's a shitty solution that is actually good enough.