Linux kernels >= 3.9 allow sharing of sockets between processes with in-kernel load-balancing by setting SO_REUSEPORT: http://lwn.net/Articles/542629/
How can this be used for sockets of type AF_UNIX?
It seems, it only works with TCP, not Unix domain sockets.
Here is a Python test program:
import os
import socket
if not hasattr(socket, 'SO_REUSEPORT'):
socket.SO_REUSEPORT = 15
if True:
# using TCP sockets
# works. test with: "echo data | nc localhost 8888"
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
s.bind(('', 8888))
else:
# using Unix domain sockets
# does NOT work. test with: "echo data | nc -U /tmp/socket1"
s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
try:
os.unlink("/tmp/socket1")
except:
pass
s.bind("/tmp/socket1")
s.listen(1)
while True:
conn, addr = s.accept()
print('Connected to {}'.format(os.getpid()))
data = conn.recv(1024)
conn.send(data)
conn.close()
Start 2 instances, and test by running the following multiple times:
echo data | nc localhost 8888for TCPecho data | nc -U /tmp/socket1for Unix domain sockets
When using TCP, the incoming clients will get balanced to both servers. With Unix domain sockets, the incoming clients all get connected to the last started server.
