[LOG4J2-1578] RoutingAppender can be configured with scripts

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Gary D. Gregory
• Reporter: Gary D. Gregory
• Created: 13/Sep/16 03:53
• Updated: 21/Nov/17 14:06

Description

RoutingAppender can be configured with scripts.

Use Case

What I need to do is only add a specific appender when running on a specific OS (USS on OS/390 if you must know). Then only add a different appender when not running on that OS.

Final Solution

Example configuration:

  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Flume name="AuditLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Routing name="Routing">
      <Script name="RoutingInit" language="groovy"><![CDATA[
         if (System.getProperty(?os.name?).contains(?OS/390") {
            return "OS390";
         }
         return null;]]>
      </Script>
      <Routes>     
        <Script name="Router" language="groovy"><![CDATA[
            if (logEvent.getMarker() != null && logEvent.getMarker().isInstanceOf("AUDIT")) {
                return "AUDIT";
            } else if (logEvent.getContextMap().containsKey("UserId")) { 
                return logEvent.getContextMap().get("UserId");
            }
            return "STDOUT";
            ]]>
          </Script> 
        <Route>
          <OS390Appender name="OS390-${mdc:UserId"/> 
          <RollingFile name="Rolling-${mdc:UserId}" fileName="${mdc:UserId}.log"
                       filePattern="${mdc:UserId}.%i.log.gz">
            <PatternLayout>
              <pattern>%d %p %c{1.} [%t] %m%n</pattern>
            </PatternLayout>
            <SizeBasedTriggeringPolicy size="500" />
          </RollingFile>
        </Route>
        <Route ref="AuditLogger" key="Audit"/>
        <Route ref="STDOUT" key="STDOUT"/>
      </Routes>
      <IdlePurgePolicy timeToLive="15" timeUnit="minutes"/>
    </Routing>
  </Appenders>

As part of this the Routes class' factory method org.apache.logging.log4j.core.appender.routing.Routes.createRoutes(String, Route...) is deprecated in favor of a builder.

Initial Solution

Posted by ralphgoers on the dev ML:

After reviewing what I wrote below and looking at the Routing Appender I think the best thing to do is just to add script support to it. It already has support for a default Route. The init script, if present, could override which Route to use as I described below. Then we could add a script attribute to the Routes plugin which could be used to select the Route instead of only matching on the ThreadContext key.

With that I think you would have everything you want, plus it could be used as a more intelligent way to route to existing appenders.

The configuration would then look like:

  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Flume name="AuditLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Routing name="Routing">
      <InitScript name="RoutingInit" language="groovy"><![CDATA[
         if (System.getProperty(?os.name?).contains(?OS/390") {
            return "OS390";
         }
         return null;]]>
      </InitScript>
      <Routes>     
        <Script name="Router" language="groovy"><![CDATA[
            if (logEvent.getMarker() != null && logEvent.getMarker().isInstanceOf("AUDIT")) {
                return "AUDIT";
            } else if (logEvent.getContextMap().containsKey("UserId")) { 
                return logEvent.getContextMap().get("UserId");
            }
            return "STDOUT";
            ]]>
          </Script> 
        <Route>
          <OS390Appender name="OS390-${mdc:UserId"/> 
          <RollingFile name="Rolling-${mdc:UserId}" fileName="${mdc:UserId}.log"
                       filePattern="${mdc:UserId}.%i.log.gz">
            <PatternLayout>
              <pattern>%d %p %c{1.} [%t] %m%n</pattern>
            </PatternLayout>
            <SizeBasedTriggeringPolicy size="500" />
          </RollingFile>
        </Route>
        <Route ref="AuditLogger" key="Audit"/>
        <Route ref="STDOUT" key="STDOUT"/>
      </Routes>
      <IdlePurgePolicy timeToLive="15" timeUnit="minutes"/>
    </Routing>
  </Appenders>

First, the init script changes the default route based on the OS.
Second, notice that "Routes" has a new Script element and does not have a pattern specified, so the script is determining the key instead of the pattern.
Third, the real default route is now "STDOUT" since the actual default Route is only referenced when a UserId is present in the thread context map.

What would also be nice is if there was a way to have the returned value be usable as a Lookup value in the default Appender definition, instead of relying on the MDC as the code above does. I should be able to pick something out of the message itself and use that as the key. That should be doable but I am still pondering how I would implement that.

Issue Links

• requires: LOG4J2-1577 Add a Builder to the RoutingAppender and deprecate factory method