Traefik with gRPC and Let's Encrypt?
To communicate in https between your traefik and your container, you need to add the label traefik.protocol=https on your container (https://docs.traefik.io/configuration/backends/docker/#on-containers)
Moreover, with the docker backend when traefik will contact your backend server, it will use the IP of the container (and it doesn't match your domain certificate). So you may can active InsecureSkipVerify in your traefik configuration (https://docs.traefik.io/configuration/commons/#main-section).