app.py

import flask
import socket
import fcntl
import struct

app = flask.Flask(__name__)


# http://stackoverflow.com/questions/24196932/how-can-i-get-the-ip-address-of-eth0-in-python
def get_ip_address(ifname):
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    return socket.inet_ntoa(fcntl.ioctl(
        s.fileno(),
        0x8915,  # SIOCGIFADDR
        struct.pack('256s', ifname[:15])
    )[20:24])


@app.route('/')
def ip():
    return get_ip_address('eth0')


if __name__ == '__main__':
    app.run()