MDC logging

Available as of Camel 2.7

From Camel 2.7: Camel uses the SLF4J logging framework. This allows Camel to support MDC logging. For more information about about MDC logging see the logback manual.

The logging framework in use must support MDC. The following frameworks support MDC:

See the logging framework's documentation for how to configure it to use MDC.

Enabling MDC Logging in Camel

To enable MDC logging using Java:

CamelContext context = ...
context.setUseMDCLogging(true);
...

To enable MDC logging using Spring XML set CamelContext's useMDCLogging attribute:

<camelContext xmlns="http://camel.apache.org/schema/spring" useMDCLogging="true">
  ...
</camelContext>

MDC Information

Camel provides the following context information available for MDC:

Before Camel 2.10:

 

Key

Description

exchangeId

The exchange id

messageId

Camel 2.9.1: The message id

correlationId

The correlation id of the exchange if it's correlated. For example a sub message from the Splitter EIP

transactionKey

The id of the transaction for transacted exchanges. Note the id is not unique, but its the id of the transaction template that marks the transaction boundary for the given transaction. Hence we decided to name the key transactionKey and not transactionID to point out this fact.

routeId

The id of the route, in which the exchange is currently being routed

breadcrumbId

Camel 2.8: An unique id used for tracking messages across transports.

camelContextId

Camel 2.8.3/2.9: the camel context id used for tracking the message from different camel context.

From Camel 2.10:

 

Key

Description

camel.exchangeId

The exchange id

camel.messageId

The message id

camel.correlationId

The correlation id of the exchange if it's correlated. For example a sub message from the Splitter EIP

camel.transactionKey

The id of the transaction for transacted exchanges. Note the id is not unique, but its the id of the transaction template that marks the transaction boundary for the given transaction. Hence we decided to name the key transactionKey and not transactionID to point out this fact.

camel.routeId

The id of the route, in which the exchange is currently being routed

camel.breadcrumbId

An unique id used for tracking messages across transports.

camel.contextId

The camel context id used for tracking the message from different camel context.

The keys are subject to change as we want to align and leverage MDC across other Apache products such as ActiveMQ, ServiceMix and Karaf.

Example Using LOG4J

If you use log4j you can configure MDC in the log4j.properties file as shown:

log4j.appender.out.layout.ConversionPattern=%d [%-15.15t] %-5p %-30.30c{1} - %-10.10X{camel.exchangeId} - %-10.10X{camel.routeId} - %m%n

Camel will log on startup if MDC is enabled or not

INFO  SpringCamelContext -            -            - MDC logging is enabled on CamelContext: camel-1

The follow snippet is from an unit test which shows MDC in use. Note that the exchange id and route id are displayed in their separate columns in the log file:

INFO  SpringCamelContext -            -            - Apache Camel  (CamelContext: camel-1) started in 1.228 seconds
INFO  foo                - 358739-0-2 - route-a    - Exchange[ExchangePattern:InOnly, BodyType:String, Body:Hello World]
INFO  bar                - 358739-0-2 - route-b    - Exchange[ExchangePattern:InOnly, BodyType:String, Body:Hello World]
INFO  MockEndpoint       -            -            - Asserting: Endpoint[mock://result] is satisfied

Enabling Breadcrumb Support

From Camel 2.8:
The breadcrumbId key for MDC logging is only available if useBreadcrumb=true has been set on the CamelContext (default is true). When enabled Camel will enrich the Camel Message by adding a header to it with the key breadcrumbId containing the id. Camel will use the messageId if no existing breadcrumbId was found in the message.

As the breadcrumb id is stored in a header it will persist across any transport that supports the use of headers, for example the HTTP and JMS transports.

Disabling Breadcrumb Support

Java DSL:

CamelContext context = ...
context.setUseBreadcrumb(false);
...

XML DSL:

<camelContext xmlns="http://camel.apache.org/schema/spring" useBreadcrumb="false">
  ...
</camelContext>