今日生产环境发现有些容器停止响应了，但是容器没有死，docker exec -it <container-name> /bin/bash也能正常使用。
在容器内部使用jstack <pid>发现log4j2的Console Appender一直处于运行状态：
"AsyncAppender-asyncConsole" #21 daemon prio=5 os_prio=0 tid=0x00007fd968d07000 nid=0x1f runnable [0x00007fd91bffd000] java.lang.Thread.State: RUNNABLE at java.io.FileOutputStream.writeBytes(Native Method) at java.io.FileOutputStream.write(FileOutputStream.java:326) at java.io.BufferedOutputStream.write(BufferedOutputStream.java:122) - locked <0x00000000f002b408> (a java.io.BufferedOutputStream) at java.io.PrintStream.write(PrintStream.java:480) - locked <0x00000000f002b3e8> (a java.io.PrintStream) at org.apache.logging.log4j.core.util.CloseShieldOutputStream.write(CloseShieldOutputStream.java:53) at org.apache.logging.log4j.core.appender.OutputStreamManager.writeToDestination(OutputStreamManager.java:262) - locked <0x00000000f021d848> (a org.apache.logging.log4j.core.appender.OutputStreamManager) at org.apache.logging.log4j.core.appender.OutputStreamManager.flushBuffer(OutputStreamManager.java:294) - locked <0x00000000f021d848> (a org.apache.logging.log4j.core.appender.OutputStreamManager) at org.apache.logging.log4j.core.appender.OutputStreamManager.drain(OutputStreamManager.java:351) at org.apache.logging.log4j.core.layout.TextEncoderHelper.drainIfByteBufferFull(TextEncoderHelper.java:260) - locked <0x00000000f021d848> (a org.apache.logging.log4j.core.appender.OutputStreamManager) at org.apache.logging.log4j.core.layout.TextEncoderHelper.writeAndEncodeAsMuchAsPossible(TextEncoderHelper.java:199) at org.apache.logging.log4j.core.layout.TextEncoderHelper.encodeChunkedText(TextEncoderHelper.java:159) - locked <0x00000000f021d848> (a org.apache.logging.log4j.core.appender.OutputStreamManager) at org.apache.logging.log4j.core.layout.TextEncoderHelper.encodeText(TextEncoderHelper.java:58) at org.apache.logging.log4j.core.layout.StringBuilderEncoder.encode(StringBuilderEncoder.java:68) at org.apache.logging.log4j.core.layout.StringBuilderEncoder.encode(StringBuilderEncoder.java:32) at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:220) at org.apache.logging.log4j.core.layout.PatternLayout.encode(PatternLayout.java:58) at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.directEncodeEvent(AbstractOutputStreamAppender.java:177) at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.tryAppend(AbstractOutputStreamAppender.java:170) at org.apache.logging.log4j.core.appender.AbstractOutputStreamAppender.append(AbstractOutputStreamAppender.java:161) at org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:156) at org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:129) at org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:120) at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:84) at org.apache.logging.log4j.core.appender.AsyncAppender$AsyncThread.callAppenders(AsyncAppender.java:459) at org.apache.logging.log4j.core.appender.AsyncAppender$AsyncThread.run(AsyncAppender.java:412)
但用docker logs -f <container-name>没有发现有新的日志输出，且访问该应用肯定会输出日志的接口也是没有任何日志输出，因此怀疑log4j2阻塞住了。
Google到有人在log4j提出了类似了问题，官方给出的解释是问题出在log4j2之外。
于是查一下logback是否也有类似问题，找到，同样给出的解释是问题出在logback之外。
两个问题的共通点都是用docker运行，于是把应用直接进程方式运行，没有出现问题。
于是Google搜索docker logging to stdout hangs，找到SO的这个，以及这个，解决方案将Docker升级到18.06。
查看生产环境的docker版本是18.03，升级到18.09后问题解决。