How to synchronize GPIO state between two Raspberry over Internet?

Question

What is the simplest way to synchronize GPIO state (states are: 1 or 0) between two Raspberry devices connected via Internet ?

What I need is immediately change GPIO state on Raspberry 1 if Raspberry 2 GPIO was changed before.

I'm thinking about bash script which read state on Raspberry 1 and send the same state to Raspberry 2 via ssh.
Something like:
ssh pi@remote-host.edu 'echo "1" > /sys/class/gpio/gpio4/value'

But I'm not sure about speed of this action.

Answer 1

My pigpio may do what you want.

You could have the pigpio daemon running on each Pi.

You could then run a Python script on one Pi. The script will be able to read/write the local GPIO as well as read/write the GPIO on the other P.

#!/usr/bin/env python

import time
import pigpio

GPIO=4

pi_local = pigpio.pi() # defaults to local Pi.
if not pi_local.connected:
   print("can't connect to local pi")

pi_remote = pigpio.pi("192.168.1.20")
if not pi_remote.connected:
   print("can't connect to remote pi")

def callback_function(gpio, level, tick):
   pi_remote.write(gpio, level) # echo level changes to remote Pi.
   print("set {} to {}".format(gpio, level))

cb = pi_local.callback(GPIO, pigpio.EITHER_EDGE, callback_function)

try:
   while True:
      time.sleep(60) # all the work is done in the callback function.
except KeyboardInterrupt:
   print("\nTidying up")

cb.cancel()
pi_remote.stop()
pi_local.stop()