Error 503: No healthy backends

[krinsman]

copied from here: #856 (comment)

I am not sure this is related to the current issue, but links to notebooks at http://qutip.org/tutorials do not work right now.
Also https://nbviewer.jupyter.org itself gives a 503 error.

Seemingly relevant threads:
#759
#758
#746
#607
#534

(This should probably be marked as a duplicate obviously, although on the other hand it would be nice to figure out a fix to prevent this from happening again in the future.)

[andreaaraldo]

Still happening today, and also in recent days to others - see #759