In GKE (Google Kubernetes Engine), setting up ingress controller and
cert-manager is straightforward.
After setting up the ingress controller and cert-manager on DO Kubernetes,
my sub-domain was still not served on https. When I checked
cert-manager logs, I found this error:
Waiting for http-01 challenge propagation: failed to perform self check GET request.
After little searching on Google I found this article on DO.
In short, add the following annotation to your ingress resource and you should be good.
service.beta.kubernetes.io/do-loadbalancer-hostname: "workaround.example.com"
Related Github issue: https://github.com/jetstack/cert-manager/issues/3238