"No server available" Error 503
I started getting this error one day. Fixed it by disabling the health check.
My setup
Pangolin on VPS
Newt tunnel to self hosted
Resources with health checks to the container at long intervals.
Background
At some point (either containers were restarted or down for some reason) the health check failed, and I was no longer able to access the resources because Pangolin simply does not route to it anymore after the health check fails. The containers were still running locally, just not routed to by Pangolin anymore.
Solution
In my case it was due to setting up Pangolin health checks to my resources (and probably the interval times were too long to reset once the containers were back up). Turned these off after making sure all my containers were working and everything went back to normal.