[Hawkular-dev] logging in java agents is not trivial in WildFly / EAP

[Thomas Heute]

Adding Dimitris and Brian (It relates to
https://issues.jboss.org/browse/WFCORE-2526 )

(Mazz I have a question below)

On Thu, Sep 28, 2017 at 5:29 PM, John Mazzitelli <mazz at redhat.com> wrote:

> <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.
>

That's for WF-Core 2.x (as in EAP 7.0), how about WF-Core 3 (as in EAP 7.1)
? IIRC you also need some of those ugliness ?

Thomas



>
> ---
>
> [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*
>
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