On Wed, Sep 6, 2017 at 6:26 PM Amit Saha <amitsaha...@gmail.com> wrote:
> On Wed, 6 Sep 2017 at 5:40 am, Ken Payson <kpay...@google.com> wrote:
>
>> On Tue, Sep 5, 2017 at 6:07 AM, Amit Saha <amitsaha...@gmail.com> wrote:
>>
>>>
>>>
>>> On Tue, Sep 5, 2017 at 9:02 AM Amit Saha <amitsaha...@gmail.com> wrote:
>>>
>>>> On Tue, 5 Sep 2017 at 6:44 am, Ken Payson <kpay...@google.com> wrote:
>>>>
>>>>> gRPC Python sets the SO_REUSEADDR option on server sockets, which
>>>>> allows multiple servers to bind to the same port.
>>>>>
>>>>
>>>> Thanks. Is there any reason why this is set to be the default behavior?
>>>>
>>>
>>> Searching around, I can see that this *may* be desired behavior and
>>> hence gRPC has made a pragmatic choice. However, it seems to be most useful
>>> in a scenario where an existing socket is in the TIME_WAIT state and we
>>> want a new server process to bind to the same addr/port. However, two
>>> questions:
>>>
>>
>>> 1. This is not the case here - both of my servers are in LISTEN
>>>
>> I think you are referring to the SO_REUSEPORT option. The SO_REUSEADDR
>> is different, and is intended for having multiple processes bind to the
>> same port. One advantage of this is that you can scale by having multiple
>> processes serving requests.
>>
>
> Sorry, but whatever I read seems to suggest the behavior you mention for
> SO_REUSEPORT and not SO_REUSEADDR. I will definitely look more, but if you
> have a handy reference you can share, that will be great.
>
I switched to Linux for my experiments this time. Let's consider the server
below:
import socket
import os
def start_server():
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind(('localhost', 5555))
sock.listen(0)
while True:
connection, address = sock.accept()
buf = connection.recv(64)
if len(buf) > 0:
print os.getpid()
if __name__ == '__main__':
start_server()
Start the instance 1:
$ lsof -i TCP:5555
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
python 10973 asaha 3u IPv4 11332922 0t0 TCP localhost:5555
(LISTEN)
If I try to start a second instance of the server, I get:
Traceback (most recent call last):
File "server.py", line 19, in <module>
start_server()
File "server.py", line 7, in start_server
sock.bind(('localhost', 5555))
File "/usr/lib/python2.7/socket.py", line 228, in meth
return getattr(self._sock,name)(*args)
socket.error: [Errno 98] Address already in use
Now if I change the server as follows to use SO_REUSEPORT:
import socket
import os
def start_server():
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
sock.bind(('localhost', 5555))
sock.listen(0)
while True:
connection, address = sock.accept()
buf = connection.recv(64)
if len(buf) > 0:
print os.getpid()
if __name__ == '__main__':
start_server()
I can start two server processes and I see both instances serving client
requests. So that tells me that SO_REUSEADDR doesn't allow a seond process
to LISTEN when another already is.
Now, let's get back to my original gRPC server. When I try to start a
second instance of the server, I get this on Linux:
E0907 12:28:57.205046525 16071 server_chttp2.c:53]
{"created":"@1504751337.205028841","description":"No address added out of
total 1
resolved","file":"src/core/ext/transport/chttp2/server/chttp2_server.c","file_line":260,"referenced_errors":[{"created":"@1504751337.205026361","description":"Unable
to configure
socket","fd":3,"file":"src/core/lib/iomgr/tcp_server_utils_posix_common.c","file_line":215,"referenced_errors":[{"created":"@1504751337.205023798","description":"OS
Error","errno":98,"file":"src/core/lib/iomgr/tcp_server_utils_posix_common.c","file_line":188,"os_error":"Address
already in use","syscall":"bind"}]}]}
Much better, this exactly what I expected. So, this tells me that the
behaviour of SO_REUSEADDR is "different" on OS X?
FWIW, I found https://github.com/veithen/knetstat useful to be able to see
the socket options set.
>>>>>>
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