容器打印日志到控制台阻塞的排障

摘要：原文今日生产环境发现有些容器停止响应了，但是容器没有死，也能正常使用。在容器内部使用发现的一直处于运行状态但用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，因此怀疑阻塞住了。

原文

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 /bin/bash也能正常使用。

在容器内部使用jstack 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 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LOG4J2-2239，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LOGBACK-1422，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的这个回答，以及这个issue，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。