[Haskell-cafe] Amazonka, conduit and sockets not closing

[Bryan Richter]

I thought CLOSE_WAIT *is* one of the "closed" states. TCP sockets
stick around for a few minutes after use, right? You may simply be
generating sockets faster than one operating system can handle. Find
some way to reuse existing sockets, perhaps?

On Thu, Nov 26, 2020 at 3:13 PM Magnus Therning <magnus at therning.org> wrote:
>
> I've run into a problem with running out of filedescriptors. The
> following snippet is a trimmed down version of what I'm doing:
>
> #+begin_src haskell
> main :: IO ()
> main = do
>   awsEnv <- newEnv Discover
>   runAWSCond awsEnv $
>     sqsSource queueUrl
>       .| C.mapC snd
>       .| sqsDeleteSink queueUrl
>   where
>     runAWSCond awsEnv = runResourceT . runAWS awsEnv . within Frankfurt . C.runConduit
>
> sqsSource :: MonadAWS m => T.Text -> C.ConduitT () (T.Text, T.Text) m ()
> sqsSource queueUrl = do
>   (_, msgs) <- C.lift $ recvSQS queueUrl
>   C.yieldMany msgs
>   sqsSource queueUrl
>
> sqsDeleteSink :: MonadAWS m => T.Text -> C.ConduitT T.Text o m ()
> sqsDeleteSink queueUrl = do
>   C.await >>= \case
>     Nothing -> pure ()
>     Just receiptHandle -> do
>       void $ C.lift $ delSQS queueUrl receiptHandle
>       sqsDeleteSink queueUrl
>
> recvSQS queueUrl = do
>   let rm = receiveMessage queueUrl & rmMaxNumberOfMessages ?~ 10
>   rmrs <- send rm
>   let status = rmrs ^. rmrsResponseStatus
>       msgs = rmrs ^. rmrsMessages & traversed %~ extract
>   pure (status, catMaybes msgs)
>   where
>     extract msg = do
>       body <- msg ^. mBody
>       rh <- msg ^. mReceiptHandle
>       pure (body, rh)
>
> delSQS queueUrl receiptHandle = do
>   let dm = deleteMessage queueUrl receiptHandle
>   send dm
> #+end_src
>
> This works fine for a while, but given a queue with enough messages it will fail
> with something like
>
> #+begin_example
> TransportError (HttpExceptionRequest Request {
>   host                 = "sqs.eu-central-1.amazonaws.com"
>   port                 = 443
>   secure               = True
>   requestHeaders       = [("Host","sqs.eu-central-1.amazonaws.com"),("X-Amz-Date","20201126T101659Z"),("X-Amz-Content-SHA256","2e4bdf20a857a1416f218b1218670cf019ff53268d0adb34fe06402a62f3271d"),("Content-Type","application/x-www-form-urlencoded; charset=utf-8"),("Authorization","<REDACTED>")]
>   path                 = "/"
>   queryString          = ""
>   method               = "POST"
>   proxy                = Nothing
>   rawBody              = False
>   redirectCount        = 0
>   responseTimeout      = ResponseTimeoutMicro 70000000
>   requestVersion       = HTTP/1.1
> }
>  (ConnectionFailure Network.Socket.getAddrInfo (called with preferred socket type/protocol: AddrInfo {addrFlags = [AI_ADDRCONFIG], addrFamily = AF_UNSPEC, addrSocketType = Stream, addrProtocol = 0, addrAddress = <assumed to be undefined>, addrCanonName = <assumed to be undefined>}, host name: Just "sqs.eu-central-1.amazonaws.com", service name: Just "443"): does not exist (System error)))
> #+end_example
>
> After some detours I found out that it's actually not a network issue, but
> rather that the process runs out of filedescriptors. Using =lsof= I can see that
> it doesn't seem to close /any/ sockets at all, instead they get stuck in a
> =CLOSE_WAIT= state:
>
> #+begin_example
> COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
> wd-stats 88674 magnus   23u  IPv4 815196      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60624->52.119.188.213:https (CLOSE_WAIT)
> wd-stats 88674 magnus   24u  IPv4 811362      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43482->52.119.189.184:https (CLOSE_WAIT)
> wd-stats 88674 magnus   25u  IPv4 811386      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:60628->52.119.188.213:https (CLOSE_WAIT)
> wd-stats 88674 magnus   26u  IPv4 813527      0t0  TCP ip-192-168-0-9.eu-central-1.compute.internal:43486->52.119.189.184:https (CLOSE_WAIT)
> ...
> #+end_example
>
> Am I using Amazonka and/or Conduit in a way that results in this? How do I should I use them?
>
> Or, is it an issue somewhere "below" my code? What can I do address that?
>
> Thanks for any insights or help
> /M
>
> --
> Magnus Therning              OpenPGP: 0x927912051716CE39
> email: magnus at therning.org
> twitter: magthe              http://magnus.therning.org/
>
> Action is the foundational key to all success.
>      — Pablo Picasso
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