Hello,

What you could do in order to fix the 521 error is to change your SSL type to Flexible SSL via your Cloudflare control panel. That way you would not have to install an SSL on your Droplet and your site would still be accessible via HTTPS.

As far as I can see according to the official wiki.js documentation, they are suggesting the approach that I’ve described above and also that they are working on a native Let’s Encrypt integration that is supposed to be coming out soon, for more information you could check the documentation here:

https://docs.requarks.io/en/install/digitalocean

Another thing that you could do is to install Nginx and set it up as a reverse proxy, that way you could install an SSL on your Droplet as well. Here’s a tutorial on how to Deploy Docker container with Nginx:

https://www.digitalocean.com/community/tutorials/how-to-deploy-a-go-web-application-with-docker-and-nginx-on-ubuntu-18-04#step-2-%E2%80%94-deploying-nginx-proxy-with-let%E2%80%99s-encrypt

IT is specifically for Go application, but you could follow the Nginx Reverse Proxy with Let’s Encrypt steps and it should work for any Dockerized application.

Hope that this helps!
Regards,
Bobby