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MDC Logging

Mapped Diagnostic Context (MDC) is a Java logging feature that allows attaching custom contextual information to each log entry.
Most major logging frameworks support MDC, and it’s often used to improve logging and monitoring in Java applications, including Apache Camel.

Limitation:
The main limitation of this technology is the fact that it stores values on a context that is available at thread level. Since Camel is an application that manages multiple thread, when it deals with asynchronous calls, the context propagation may not work correctly.

1. Enable MDC in application.properties

camel.main.useMdcLogging=true
camel.main.mdcLoggingKeysPattern=correlationid
- camel.main.mdcLoggingKeysPattern - Defines which MDC keys to propagate during asynchronous message routing.

2. Configure Logging (log4j2.properties)

status = warn
name = MDCLogging

############################
# Appenders
############################
# Route logs: include correlationid and camel.routeId with ANSI colors
appender.route.type = Console
appender.route.name = ROUTE_APP
appender.route.target = SYSTEM_OUT
appender.route.layout.type = PatternLayout
appender.route.layout.disableAnsi = false
appender.route.layout.pattern = [%d{yyyy-MM-dd HH:mm:ss.SSS} - %highlight{%p{length=3}}{FATAL=bg_red bold, ERROR=red bold, WARN=yellow bold, INFO=green bold, DEBUG=blue bold, TRACE=cyan bold}] [%style{%X{correlationid}}{cyan bold}] [%style{%X{camel.routeId}}{green bold}] %m%n

# Default console
appender.stdout.type = Console
appender.stdout.name = out
appender.stdout.target = SYSTEM_OUT
appender.stdout.layout.type = PatternLayout
appender.stdout.layout.pattern = %style{%d{yyyy-MM-dd HH:mm:ss.SSS}}{Dim} %highlight{%5p} %style{%pid}{Magenta} %style{---}{Dim} %style{[%15.15t]}{Dim} %style{%-40.40c}{Cyan} %style{:}{Dim} %m%n

############################
# Loggers
############################
# Your route logs (use log:route in route)
logger.route.name = route
logger.route.level = info
logger.route.additivity = false
logger.route.appenderRefs = route
logger.route.appenderRef.route.ref = ROUTE_APP

############################
# Root
############################
rootLogger.level = info
rootLogger.appenderRefs = out
rootLogger.appenderRef.out.ref = out

3. Set a Custom MDC Key

In Java

org.slf4j.MDC.put("correlationid", "CUSTOM_KEY_VALUE");

In Camel YAML DSL (Groovy script processor): 

- script:
    id: script-be41
    expression:
      groovy:
        id: groovy-47e8
        expression: >-
          org.slf4j.MDC.put("correlationid", "CUSTOM_KEY_VALUE")

4. Use the Custom Logger

- log:
    id: log-1b81
    message: body
    loggingLevel: INFO
    logName: route

Additional Resources Apache Camel MDC Documentation