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

[Brian Stansberry]

I've copied James Perkins, who is the WildFly logging component lead.

Brian Stansberry
Manager, Senior Principal Software Engineer
Red Hat

On Fri, Sep 29, 2017 at 3:35 AM, Thomas Heute <theute at redhat.com> wrote:

> 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=o
>> rg.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.cla
>> ss.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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>>
>
>
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