10:29 a.m.
<tl;dr>
No matter if a java agent uses JBoss Logging or simply relies on the JRE's own Java
logging, it still won't work in WildFly/EAP unless you set additional things to
environment variables in standalone.conf. So no matter what logging is used, this means
problems still need to be overcome when putting java agents in host controllers for EAP
7.0 domain mode.
</tl;dr>
I am looking at how Java Agents should log messages when attached to WildFly or EAP. I
want to see if there is a way to implement a Java Agent and NOT have to set any special
JAVA_OPTS values to pass to the VM to get it to work.
Turns out, it is not a trivial issue.
I wrote a silly little test agent [1] just to see what would happen if it simply logs a
message using *java* logging and spins a thread logging a message every second again using
*java* logging. So, no extra third party logging libraries, just using java.util.logging
classes that are in the JRE already.
Adding just -javaagent to JAVA_OPTS (in standalone.conf, add something like
"-javaagent:/where/it/is/ja.jar=foo=bar") is no good, the server bombs with this
error, presumably because my agent already started logging using java logger:
Caused by: java.util.concurrent.ExecutionException: java.lang.IllegalStateException:
WFLYLOG0078: The logging subsystem requires the log manager to be
org.jboss.logmanager.LogManager. The subsystem has not be initialized and cannot be used.
To use JBoss Log Manager you must add the system property
"java.util.logging.manager" and set it to
"org.jboss.logmanager.LogManager"
Well, catch-22, because if I set java.util.logging.manager=org.jboss.logmanager.LogManager
in JAVA_OPTS, this happens when the test agent tries to log:
Could not load Logmanager "org.jboss.logmanager.LogManager"
java.lang.ClassNotFoundException: org.jboss.logmanager.LogManager
which then falls back to java logging, which then causes the server to bomb again because
it wants JBoss Logging.
If I set this in standalone.conf:
JBOSS_MODULES_SYSTEM_PKGS="org.jboss.byteman,org.jboss.logmanager"
the java agent still gets this error:
Could not load Logmanager "org.jboss.logmanager.LogManager"
java.lang.ClassNotFoundException: org.jboss.logmanager.LogManager
which is then followed by jboss modules error which causes the server to again to fail to
start:
WARNING: Failed to load the specified log manager class
org.jboss.logmanager.LogManager
Exception in thread "main" java.lang.NoClassDefFoundError:
org/jboss/logmanager/Level
...
at org.jboss.modules.Module.run(Module.java:320)
The ONLY way to get the server to start properly with this java agent installed (EVEN WITH
the agent using ONLY java logging), you have to do all of the above plus add this to
JAVA_OPTS:
-Xbootclasspath/p:$JBOSS_HOME/modules/system/layers/base/org/jboss/logmanager/main/jboss-logmanager-2.0.4.Final.jar
So, in short, you need to add
"-Djava.util.logging.manager=org.jboss.logmanager.LogManager" to JAVA_OPTS, you
need to add ",org.jboss.logmanager" to JBOSS_MODULES_SYSTEM_PKGS, and you need
to add that -Xbootclasspath to JAVA_OPTS just to get a javaagent to work even if the
javaagent simply uses nothing more than standard java logging.
---
[1] $ cat JavaAgent.java
import java.util.logging.*;
public class JavaAgent {
private static final Logger log = Logger.getLogger(JavaAgent.class.getName());
public static void premain(String args) {
log.severe("log in premain: " + args);
new Thread(new Runnable() {
public void run() {
while (true) {
try {
Thread.sleep(1000);
log.severe("log in premain loop: " + args);
} catch (Exception e) {
return;
}
}
}
}).start();
}
}
To build it:
$ echo "Premain-Class: JavaAgent" > manifest.mf
$ javac JavaAgent.java
$ jar cvfm ja.jar manifest.mf JavaAgent*