Append specific MDC field into logstash log

Question

I am trying add custom field into logstash appender in logback-spring.xml like that:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<appender name="stash" class="net.logstash.logback.appender.LogstashSocketAppender">
        <host>xx.xx.xx.xx</host>
        <port>xxxxx</port>
        <encoder class="net.logstash.logback.encoder.LogstashEncoder">
            <includeMdcKeyName>myField</includeMdcKeyName>
        </encoder>
</appender>

<root level="info">
    <appender-ref ref="stash" />
</root>

</configuration>

It gives me error:

Exception in thread "main" java.lang.IllegalStateException: Logback configuration error detected: ERROR in ch.qos.logback.core.joran.spi.Interpreter@34:71 - no applicable action for [encoder], current ElementPath is [[configuration][appender][encoder]]

When I tried console appender and I tried print that field like in sample below it worked.

<layout>
      <Pattern>%-4r [%thread] %-5level My Field: [%X{myField:--}] %msg%n</Pattern>
</layout>

Can you tell me what I did wrong with udp appender? Thank you in advice.

Answer 1

You're using an UDP appender, and it does not have an encoder. You should use TCP Appender (LogstashTcpSocketAppender instead of LogstashSocketAppender):

<appender name="stash" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
    <destination>xx.xx.xx.xx:xxxxx</destination>
    <encoder class="net.logstash.logback.encoder.LogstashEncoder">
        <includeMdcKeyName>myField</includeMdcKeyName>
    </encoder>
</appender>

---

Take a look a demo project I've created here.

This code (Kotlin):

MDC.put("mdc", "so53558553")

LOG.warn("Warn")

With a logback-spring.xml like this:

<appender name="logstash" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
    <destination>localhost:5000</destination>
    <encoder class="net.logstash.logback.encoder.LogstashEncoder">
        <includeMdcKeyName>mdc</includeMdcKeyName>
    </encoder>
</appender>

Produces such records in Logstash:

{
    "level_value" => 30000,
            "mdc" => "so53558553",
           "port" => 35450,
    "logger_name" => "by.dev.madhead.playgrounds.so53558553.SpringBootConsoleApplication",
           "host" => "172.17.0.1",
       "@version" => "1",
     "@timestamp" => 2018-12-03T01:16:28.793Z,
    "thread_name" => "main",
        "message" => "Warn",
          "level" => "WARN"
}

As you see, mdc values are seen by Logstash as a field in the LoggingEvent.

EDIT

You may not see your field in Kibana due to an ELK misconfiguration. I'm pasting my Logstash pipiline config (/etc/logstash/conf.d/01-input.conf) just for the reference (it's very basic):

input {
    tcp {
        port => 5000
        codec => json_lines
    }
}

output {
    elasticsearch {
        hosts => [ "localhost:9200" ]
        index => "logback-%{+YYYY.MM.dd}"
    }
}

Then I've configured logs in Kibana with logback-* pattern:

And voila: