greenlock-express.js | Free SSL and Automatic HTTPS | TLS library

I have an app with the following structure:

• An R Shiny app which functions as a UI and it lets the user upload files and stores them on a gcePersistentDisk.
• A node.js server which reads those files on the gcePersistentDisk processes them and provides an API for the Shiny app to retrieve the results.

This runs in a GKE cluster with the following structure:

• a StatefulSet with a pod containing two containers to allow simultaneous access for both the client and the server to the volume.
• a headless service for the StatefulSet.
• an Ingress with a fixed IP to where the domain points.
• a NodePort as a backend for the Ingress with the selector pointing to the 0th pod of the StatefulSet

At least this is what I did to make this work, I'm not too good in DevOps or networking in general. Now the client came up with a request that a third party app would also use the node.js API but it wishes to do so on https.

My first try was to use greenlock-express.js, however, it needs a public facing IP, but the server can only see it's cluster IP. I don't know if this could/should be changed and if not what other approaches should I take?

Thanks!

YAML's