[Python] OSError 99 while starting socketserver on boot, Debian

I wrote a simmple TCP server using socketserver module. It runs and functions perfectly well when running it through bash like

python scpi_server.py
​

Here is the simplified code:

if __name__ == "__main__":
HOST, PORT = "10.121.1.36", 9999 # Listen on strict IP given to my by company DHCP on port 9999
server = socketserver.TCPServer((HOST, PORT), ScpiRequestHandler)
print(f"Server started on: {server.server_address}")
server.serve_forever() # Start the server


The handler looks as such:

class ScpiRequestHandler(socketserver.BaseRequestHandler):
def handle(self):
while True:
data = self.request.recv(1024).decode('utf-8')
if not data:
break
for cmd in data.split(';'):
try:
cmd = ScpiParser.parse(cmd)
except TypeError:
#abort if failed
return

answer = BusHandler.apply(cmd)

if answer is not None:
self.request.sendall(answer.encode('utf-8'))



As I said the program runs flawlessly if I execute it myself but I tried to make it run on boot by:

1. Creating scpi_server.service in ~etc/systemd/system~
2. Giving it permissions by ~chmod +x /path/to/scpi_server.py~
3. Reloading by ~sudo systemctl daemon-reload~
4. Enabling the service by ~sudo systemctl enable scpi_server.service~

The content of scpi_server.service is:

[Unit]
Description=My Python Script
After=network.target
Wants=network.target

[Service]
ExecStart=/usr/bin/python3 /pathto/scpi_server.py
WorkingDirectory=/pathto/
User=root #the user i usually loginto
StandardOutput=journal
StandardError=journal
Restart=always

[Install]
WantedBy=multi-user.target


If I call ~systemctl status scpi_server.service~ I can see it running if I manually started it first with ~sudo systemctl enable scpi_server.service~, but not on reboot. If I go into the log files I see the error raised by => server = socketserver.TCPServer((HOST, PORT), ScpiRequestHandler)

Traceback (most recent call last): File "/root/RaspIO_gpio_interf/scpi_server.py", line 61, in server = socketserver.TCPServer((HOST, PORT), ScpiRequestHandler) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/lib/python3.11/socketserver.py", line 456, in init self.server_bind() File "/usr/lib/python3.11/socketserver.py", line 472, in server_bind self.socket.bind(self.server_address) OSError: [Errno 99] Cannot assign requested address
​

The application crashes, tries to restart, crashes, tries to restart, crashes....

Im running the scpi server on a Debian Raspberry 4 that gets its IP address strictly from company DHCP so there is no room to play with that (and the app runs fine if i run it manually...) I am pretty lost on what to do. Please advise. Thank you


Thank you @JuliusB for the help. I just had to change "After=network-online.target" and "Wants=network-online.target" and now it turns on and functions as expected.

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