[undertow-dev] Too many open files: Exception accepting request, closing server channel TCP server (NIO)

[David Lloyd]

Once you exceed the high water mark, what you should be seeing in
netstat on the client side are connections waiting in SYN_SENT.  They
shouldn't even appear on the server's netstat, even if the client
closes and re-opens the connection (I've verified this experimentally
at the socket level).  You are correct that connections in CLOSE_WAIT
indicate that somehow the HTTP server is not correctly terminating the
connection; under most normal HTTP 1.1 operational scenarios, there
should be very few CLOSE_WAIT connections at any given time.

The next step would be diagnosing why the server is not closing
connections promptly.

On Mon, Mar 2, 2020 at 7:19 AM Nishant Kumar <nishantkumar35 at gmail.com> wrote:
>
> It feels like CLOSE_WAIT connection are not getting closed properly. Although not sure. If we reduce NO_REQUEST_TIMEOUT to small value, i can see that CLOSE_WAIT are comparatively (number decrease faster) low but still very high overall.
>
> On Mon, Mar 2, 2020, 2:29 PM Nishant Kumar <nishantkumar35 at gmail.com> wrote:
>>
>> Generally, clients also close the connection after a few thousand requests other than normal fatal conditions. There might be other cases too but I am not aware of it. They keep initiating new connections if we are not responding within the threshold time frame. This is a server to server communication system.
>>
>> On Mon, Mar 2, 2020 at 10:26 AM Stuart Douglas <sdouglas at redhat.com> wrote:
>>>
>>> This sounds like a bug, when the client closes the connection it should wake up the read listener, which will read -1 and then cleanly close the socket.
>>>
>>> Are the clients closing idle connections or connections processing a request?
>>>
>>> Stuart
>>>
>>> On Mon, 2 Mar 2020 at 14:31, Nishant Kumar <nishantkumar35 at gmail.com> wrote:
>>>>
>>>> I agree that it's a load-balancing issue but we can't do much about it at this moment.
>>>>
>>>> I still see issues after using the latest XNIO (3.7.7) with Undertow. what I have observed it that when there is a spike in request and CONNECTION_HIGH_WATER is reached, the server stops accepting new connection as expected and the client starts to close the connection because of delay (we have strict low latency requirement < 100ms) and try to create new connection again (which will also not be accepted) but server has not closed those connections (NO_REQUEST_TIMEOUT = 6000) and there will be high number of CLOSE_WAIT connections at this moment. The server is considering CLOSE_WAIT + ESTABLISHED for CONNECTION_HIGH_WATER (my understanding).
>>>>
>>>> Is there a way that I can close all  CLOSE_WAIT connection at this moment so that connection counts drop under CONNECTION_HIGH_WATER and we start responding to newly established connections? or any other suggestions? I have tried removing CONNECTION_HIGH_WATER and relying on the FD limit but that didn't work.
>>>>
>>>> On Sun, Mar 1, 2020 at 7:47 AM Stan Rosenberg <stan.rosenberg at gmail.com> wrote:
>>>>>
>>>>> On Sat, Feb 29, 2020 at 8:18 PM Nishant Kumar <nishantkumar35 at gmail.com> wrote:
>>>>>>
>>>>>> Thanks for the reply. I am running it under supervisord and i have updated open file limit in supervisord config. The problem seems to be same as what @Carter has mentioned. It happens mostly during sudden traffic spike and then sudden increase (~30k-300k) of TIME_WAIT socket.
>>>>>
>>>>>
>>>>> The changes in https://github.com/xnio/xnio/pull/206/files#diff-23a6a7997705ea72e4016c11bf9d214bR453 are likely to improve the exceptional case of exceeding the file descriptor limit. However, if you're already setting the limit too high (e.g., in our case it was 795588), then exceeding it is a symptom of not properly load-balancing your traffic; with that many connections, you'd better have a ton of free RAM available.
>>>>
>>>>
>>>>
>>>> --
>>>> Nishant Kumar
>>>> Bangalore, India
>>>> Mob: +91 80088 42030
>>>> Email: nishantkumar35 at gmail.com
>>>> _______________________________________________
>>>> undertow-dev mailing list
>>>> undertow-dev at lists.jboss.org
>>>> https://lists.jboss.org/mailman/listinfo/undertow-dev
>>
>>
>>
>> --
>> Nishant Kumar
>> Bangalore, India
>> Mob: +91 80088 42030
>> Email: nishantkumar35 at gmail.com
>
> _______________________________________________
> undertow-dev mailing list
> undertow-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/undertow-dev



-- 
- DML