Logback AsyncAppender not writing logs to underlying appenders - logback

Question

In logback.xml of my application I have an AsyncAppender defined as below.
<appender name="socketAppender" class="ch.qos.logback.classic.net.SocketAppender">
<param name="RemoteHost" value="127.0.0.1" />
<param name="Port" value="15000" />
<param name="ReconnectionDelay" value="10" />
<param name="Threshold" value="DEBUG" />
</appender>
<appender name="appLog" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>logs/myApp.log</file>
<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
<fileNamePattern>logs/myApp.%d{yyyyMMdd.HH}00.log</fileNamePattern>
</rollingPolicy>
<encoder>
<charset>UTF-8</charset>
<pattern>[%d{yyyy/MM/dd HH:mm:ss.SSS}][%p][%c{0}] %m%n]</pattern>
</encoder>
</appender>
<appender name="AsyncLog" class="ch.qos.logback.classic.AsyncAppender">
<appender-ref ref="appLog" />
<appender-ref ref="socketAppender" />
</appender>
When I deploy the war in Tomcat on Windows 10.
The log server listening on port 15000 wasn't receiving logs.
So I moved up the socketAppender to first position like below.
<appender name="AsyncLog" class="ch.qos.logback.classic.AsyncAppender">
<appender-ref ref="socketAppender" />
<appender-ref ref="appLog" />
</appender>
With this change log server started receiving logs, but the log file stopped writing/appending.
3) I also tried setting the queueSize and discardingThreshold properties on the appender, to no avail.
<discardingThreshold>0</discardingThreshold>
<queueSize>500</queueSize>
Can any logback experts please tell me what I am doing wrong here? Are there any other properties of AsyncAppender that may help fix this behaviour?

Answer 1

A colleague pointed me to this method in the class ch.qos.logback.core.AsyncAppenderBase. AsyncAppender can attach only one appender and ignores any more appenders added beyond that.
public void addAppender(Appender<E> newAppender) {
if (appenderCount == 0) {
appenderCount++;
addInfo("Attaching appender named [" + newAppender.getName() + "] to AsyncAppender.");
aai.addAppender(newAppender);
} else {
addWarn("One and only one appender may be attached to AsyncAppender.");
addWarn("Ignoring additional appender named [" + newAppender.getName() + "]");
}
}