Python Flask Server send_file fails when SSH terminal disconnected

Question

I think this would be a useful question to others too.

I have a flask server running (on an EC2) and delivers attachments via
python send_file as a request. Works great. It also provides a list of the
files available. (Using your browser). 
The process is 
I SSH to the terminal start the python3 minflask.py &

I exit the SSH. All commands work for the minflask.py accept the
send_file which says server error. I know the process is running.
I can SSH again and see the process is running.

So instead (what works) the process is

SSH for the terminal
tmux new -s mywindow
python3 minflask.py

and all works. I close the SSH terminal and all works fine.
Later I can
tmux a -t mywindow
and see my Flask server output information.

So what is the real issue HERE?

I have tried send_file with an fp=open and send_from_directory
and so on. No difference. I know I can open files.

Answer

The issue may be in the keepalive settings of your app. Or better the timeout of the sessions where your app stands in.
Usually you would use a **screen** function on Linux to keep the session up even if your not logged.

Try to modify your **supervisord** as follows to mimick **tmux** or **screen** functions.

```
[program:minflask]
command=python3 minflask.py
directory=/path/to/your/app
autostart=true
autorestart=true
stderr_logfile=/var/log/minflask.err.log
stdout_logfile=/var/log/minflask.out.log
```

Python Flask Server send_file fails when SSH terminal disconnected

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