[erlang-questions] eaddrinuse on connect ?

[Tomas Abrahamsson]

>> Hello,
>>
>> When a lot, of outgoing connections are open, I can sometimes see
>> eaddrinuse error on outgoing TCP connect.
>> As the error is obvious for binding/listening to a local socket, I was
>> wondering why this error could occur and how to avoid it.
>
> i think that, for TCP, you need a socket on the sending computer, too.
> for ack/nack, flow control, etc.

Yes, that's true. Each TCP/IP connection can be defined
as a tuple {LocalIP, LocalPort, RemoteIP, RemotePort},
and I think what may be happening is that you're
running out of TCP/IP port numbers (for LocalPort).
These are 16 bits.

>> Can using the reuseaddr parameter help in this situation ?
>
> yes, it should allow you to open the outgoing socket. perhaps you would
> get into trouble if the previous remote computer is still sending things
> back to your local/sending computer. but the sequence number should
> protect you from that... i think it will be ok.

I've never tried the reuseaddr on sockets for outgoing
connects, but here are a couple more ideas, which may
or may not be suitable for you, depending on your setup:

* Set up more IP-numbers on the box and bind to them
  when connecting (ie: set the ip option to
  gen_tcp:connect/3,4)

  (This increases the range of available {LocalIP,LocalPort}
  addresses)

* Decrease the time for the TIME_WAIT and/or CLOSE_WAIT
  states. Here are some examples of how to set it to 30 seconds:

  Solaris: /usr/sbin/ndd -set /dev/tcp tcp_time_wait_interval 30000
  Linux:   /sbin/sysctl -w net.ipv4.tcp_fin_timeout=30

  (This will cause closed connections to return to the
  pool of available addresses faster, and can be used
  e.g. in lab setups where you know you have a fast
  network and there will never be any very late packets)

* Use more machines for setting up connections

  (This reduces the range of {LocalIP,LocalPort} being
  used on each machine)

BRs
Tomas