wrote this as a comment when that article was posted to YC:

tl;dr: author looks at secret management services and reviews them

KeyWhiz: Provides everything you need but with complex PKI management, meaning setup and maintenance is a pain. Secure.

Vault: A+ would test again. Awesome rotation policies, on-demand secret generation via backends, master key sharing. Legit and secure, everything you need but has to be configured on top of your cluster.

Docker: Super easy to use, and it's built in. 10/10 would use again. Keys encrypted at rest, keys encrypted over the wire, and shared with only nodes who need them. Secure all round

Kube: Totally insecure. Plaintext at rest, plaintext over the network, shared everywhere. Basically a plaintext POC