UNDERTOW-1204 mod_cluster proxy: set default value of cacheConnections (smax) to 1

[frapex]

The default value of cacheConnections (smax) is currently set to 8. This is the number of idle connections that will be kept alive per IO thread. ioThreads is set to the number of available processors with a minimum of 2 (Undertow.java).

These idle connections unnecessarily consume cpu, memory and network resources. This becomes a big issue in large scale environments with over 4100 backend servers (4100 (backend servers) * 8 (conns) * 2 (iothreads) = 65600 idle connections, TCP stack only supports up to 65535 ports).

By setting the default value of cacheConnections (smax) to 1, idle connections timeout when they reach their ttl, not before. There is no performance impact. The default value can still be overriden client-side by setting smax in the mod_cluster configuration.

[undertow-pull-request]

Windows Build 2222 outcome was FAILURE using a merge of 8d50105
Summary: Tests failed: 1, passed: 2970, ignored: 613 Build time: 00:38:20

Failed tests

io.undertow.server.handlers.ReceiverTestCase.testAsyncReceiveWholeBytesFailed[proxy][http2]: java.lang.AssertionError
	at io.undertow.server.handlers.ReceiverTestCase.testAsyncReceiveWholeBytesFailed(ReceiverTestCase.java:194)
------- Stderr: -------
08:30:46,574 DEBUG (XNIO-1 I/O-4) [io.undertow.server.handlers.proxy] <ProxyHandler.java:531> Sending request ClientRequest{path='/fullbytes', method=POST, protocol=HTTP/1.1} to target localhost/127.0.0.1:8888 for exchange HttpServerExchange{ POST /fullbytes request {Content-Length=[130000100], Host=[localhost]} response {}}
08:30:46,577 DEBUG (XNIO-1 I/O-4) [io.undertow.server.handlers.proxy] <ProxyHandler.java:548> Sent request ClientRequest{path='/fullbytes', method=POST, protocol=HTTP/1.1} to target 127.0.0.1 for exchange HttpServerExchange{ POST /fullbytes request {Content-Length=[130000100], Host=[localhost]} response {}}
08:30:46,824 ERROR (XNIO-1 I/O-4) [io.undertow.proxy] <ProxyHandler.java:644> UT005028: Proxy request to /fullbytes failed: java.nio.channels.ClosedChannelException
	at io.undertow.client.http2.Http2ClientConnection$1.handleEvent(Http2ClientConnection.java:108)
	at io.undertow.client.http2.Http2ClientConnection$1.handleEvent(Http2ClientConnection.java:100)
	at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92)
	at io.undertow.server.protocol.framed.AbstractFramedChannel$FrameCloseListener.handleEvent(AbstractFramedChannel.java:1034)
	at io.undertow.server.protocol.framed.AbstractFramedChannel$FrameCloseListener.handleEvent(AbstractFramedChannel.java:948)
	at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92)
	at io.undertow.protocols.ssl.SslConduit$SslReadReadyHandler.terminated(SslConduit.java:1186)
	at org.xnio.nio.NioSocketConduit.readTerminated(NioSocketConduit.java:360)
	at org.xnio.nio.NioSocketStreamConnection.notifyReadClosed(NioSocketStreamConnection.java:148)
	at org.xnio.Connection.close(Connection.java:139)
	at org.xnio.IoUtils.safeClose(IoUtils.java:134)
	at io.undertow.protocols.ssl.SslConduit.closed(SslConduit.java:1021)
	at io.undertow.protocols.ssl.SslConduit.close(SslConduit.java:1092)
	at io.undertow.protocols.ssl.UndertowSslConnection.closeAction(UndertowSslConnection.java:149)
	at org.xnio.Connection.close(Connection.java:132)
	at org.xnio.IoUtils.safeClose(IoUtils.java:134)
	at io.undertow.server.protocol.framed.AbstractFramedChannel.close(AbstractFramedChannel.java:789)
	at org.xnio.IoUtils.safeClose(IoUtils.java:134)
	at io.undertow.protocols.http2.Http2Channel.sendGoAway(Http2Channel.java:824)
	at io.undertow.protocols.http2.Http2Channel.sendGoAway(Http2Channel.java:801)
	at io.undertow.client.http2.Http2ClientConnection.close(Http2ClientConnection.java:313)
	at org.xnio.IoUtils.safeClose(IoUtils.java:134)
	at io.undertow.server.handlers.proxy.ProxyHandler$IoExceptionHandler.handleException(ProxyHandler.java:772)
	at org.xnio.ChannelListeners.invokeChannelExceptionHandler(ChannelListeners.java:126)
	at io.undertow.util.Transfer$TransferListener.handleEvent(Transfer.java:218)
	at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92)
	at io.undertow.server.protocol.framed.AbstractFramedStreamSinkChannel$1.run(AbstractFramedStreamSinkChannel.java:214)
	at io.undertow.server.protocol.framed.AbstractFramedChannel$3.run(AbstractFramedChannel.java:230)
	at org.xnio.nio.WorkerThread.safeRun(WorkerThread.java:582)
	at org.xnio.nio.WorkerThread.run(WorkerThread.java:466)

08:30:46,825 DEBUG (XNIO-1 I/O-6) [io.undertow.request.io] <AbstractFramedChannel.java:813> Marking reads broken on channel Http2Channel peer /127.0.0.1:63877 local 0.0.0.0/0.0.0.0:8888[ No Receiver [] -- [] -- []]: java.nio.channels.ClosedChannelException
	at io.undertow.server.protocol.framed.AbstractFramedChannel.markReadsBroken(AbstractFramedChannel.java:813)
	at io.undertow.server.protocol.framed.AbstractFramedChannel.receive(AbstractFramedChannel.java:470)
	at io.undertow.server.protocol.http2.Http2ReceiveListener.handleEvent(Http2ReceiveListener.java:109)
	at io.undertow.server.protocol.http2.Http2ReceiveListener.handleEvent(Http2ReceiveListener.java:60)
	at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92)
	at io.undertow.server.protocol.framed.AbstractFramedChannel$FrameReadListener.handleEvent(AbstractFramedChannel.java:921)
	at io.undertow.server.protocol.framed.AbstractFramedChannel$FrameReadListener.handleEvent(AbstractFramedChannel.java:902)
	at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92)
	at org.xnio.conduits.ReadReadyHandler$ChannelListenerHandler.readReady(ReadReadyHandler.java:66)
	at io.undertow.protocols.ssl.SslConduit$SslReadReadyHandler.readReady(SslConduit.java:1145)
	at io.undertow.protocols.ssl.SslConduit$1.run(SslConduit.java:168)
	at org.xnio.nio.WorkerThread.safeRun(WorkerThread.java:582)
	at org.xnio.nio.WorkerThread.run(WorkerThread.java:466)