Why am I getting a "connection failed" error window in my Jupyter notebook?
A common issue you’ll see with a Jupyter notebook is a real scary and confusing one!
Connection failed
A connection to the notebook server could not be established. The notebook will continue trying to reconnect. Check your network connection or notebook server configuration.This probably happened because you shut down the notebook server. This usually happens because you closed the Terminal/Command Prompt/Cmder/iTerm2 window where you were running the jupyter notebook command.
To fix: Run jupyter notebook again, and re-save the notebook once the server is started. You’ll need to re-run all of the cells, but it should work.