kubernetes nginx ingress controller / caching static assets
In case somebody else stumbles upon this (probably be me in the future), the annotation is nginx.ingress.kubernetes.io/server-snippet.
Support for server-snippets annotation was added in nginx-0.9.0-beta.16. Upgrade your ingress controller image to quay.io/kubernetes-ingress-controller/nginx-ingress-controller:0.9.0-beta.16