If you see the following error when run Rancher server 2.0 preview, it could be caused by your proxy. This is NOT the proxy settings in the docker daemon but the one inside the container itself.
I noticed that Rancher server 2.0 tries to download some machine drivers when boots up, it returns the 403 error if the download fails. To fix it, you have to pass the proxy environment variables to the container. This is how I fixed it:
docker run -d –restart=unless-stopped -e https_proxy=’http://<proxy-ip>:<proxy-port>‘ -p 80:8080 rancher/server:preview