Retrieve MDC values in logback

Question

I am trying to log the MDC values in stdout and in logstash.

<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%-5level [%thread] %logger{0}: %msg -someName=%X{mdcFieldKey} %n</pattern>
            <charset>utf8</charset>
        </encoder>
    </appender>

    <appender name="logstash" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
        <destination>kibanaurl:port</destination>
        <encoder class="net.logstash.logback.encoder.LogstashEncoder">
            <customFields>
                {
                "application-name":"${spring.application.name}",
                "someName":"${mdcFieldKey}",
                "dummyName":"dummyValue"
                }
            </customFields>
            <provider class="net.logstash.logback.composite.loggingevent.ArgumentsJsonProvider"/>
        </encoder>
    </appender>

Java code:

MDC.put("mdcFieldKey", "value to be displayed in kibana");

The STDOUT appender is displaying the mdc value correctly on kibana but for the logstash appender I see someName_IS_UNDEFINED. The hardcoded dummyname is also displayed correctly.

Why is the mdc value not populated in logstash custom field?

https://stackoverflow.com/questions/41282864/logback-logstash-add-properties-in-the-logback-and-send-them-to-logstash — firstpostcommenter, Sep 28 '21 at 11:03
https://github.com/logstash/logstash-logback-encoder#mdc-fields — firstpostcommenter, Sep 28 '21 at 11:22
https://stackoverflow.com/questions/57871169/how-does-tomcat-serve-multiple-requests-with-same-thread-simulatenouly — firstpostcommenter, Sep 28 '21 at 12:57
https://stackoverflow.com/questions/45627647/how-tomcat-handle-multiple-concurrent-request-at-the-same-time — firstpostcommenter, Sep 28 '21 at 14:55

score 1 · Accepted Answer · answered Sep 28 '21 at 11:30

check here https://github.com/logstash/logstash-logback-encoder#mdc-fields

Add the line <includeMdcKeyName>mdcFieldKey</includeMdcKeyName> as below is one option. The field name will be same as mdc key in this case

<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%-5level [%thread] %logger{0}: %msg -someName=%X{mdcFieldKey} %n</pattern>
            <charset>utf8</charset>
        </encoder>
    </appender>

    <appender name="logstash" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
        <destination>kibanaurl:port</destination>
        <encoder class="net.logstash.logback.encoder.LogstashEncoder">
            <includeMdcKeyName>mdcFieldKey</includeMdcKeyName>
            <customFields>
                {
                "application-name":"${spring.application.name}",
                "dummyName":"dummyValue"
                }
            </customFields>
            <provider class="net.logstash.logback.composite.loggingevent.ArgumentsJsonProvider"/>
        </encoder>
    </appender>

Retrieve MDC values in logback

1 Answers1