Github user sjcorbett commented on a diff in the pull request:
https://github.com/apache/incubator-brooklyn/pull/762#discussion_r35201850
--- Diff: docs/guide/dev/tips/troubleshooting-exceptions.md ---
@@ -0,0 +1,487 @@
+---
+layout: website-normal
+title: Troubleshooting Exceptions and Node Failure
+toc: /guide/toc.json
+---
+
+Whether you're customizing out-of-the-box blueprints, or developing your
own custom blueprints, you will
+inevitably have to deal with node failure, or exceptions being thrown by
your node. Thankfully Brooklyn
+provides plenty of information to help you locate and resolve any issues
you may encounter.
+
+This guide looks at three common failure scenarios and describes the steps
that can be taken to
+identify the issue.
+
+## Script failure
+Many blueprints run bash scripts as part of the installation. This section
highlights how to identify a problem with
+a bash script.
+
+First let's take a look at the `customize()` method of the Tomcat server
blueprint:
+
+{% highlight java %}
+ @Override
+ public void customize() {
+ newScript(CUSTOMIZING)
+ .body.append("mkdir -p conf logs webapps temp")
+ .failOnNonZeroResultCode()
+ .execute();
+
+ copyTemplate(entity.getConfig(TomcatServer.SERVER_XML_RESOURCE),
Os.mergePaths(getRunDir(), "conf", "server.xml"));
+ copyTemplate(entity.getConfig(TomcatServer.WEB_XML_RESOURCE),
Os.mergePaths(getRunDir(), "conf", "web.xml"));
+
+ // Deduplicate same code in JBoss
+ if (isProtocolEnabled("HTTPS")) {
+ String keystoreUrl =
Preconditions.checkNotNull(getSslKeystoreUrl(), "keystore URL must be specified
if using HTTPS for " + entity);
+ String destinationSslKeystoreFile = getHttpsSslKeystoreFile();
+ InputStream keystoreStream =
resource.getResourceFromUrl(keystoreUrl);
+ getMachine().copyTo(keystoreStream, destinationSslKeystoreFile);
+ }
+
+ getEntity().deployInitialWars();
+ }
+{% endhighlight %}
+
+Here we can see that it's running a script to create four directories
before continuing with the customization. Let's
+introduce an error by changing `mkdir` to `mkrid`:
+
+{% highlight java %}
+ newScript(CUSTOMIZING)
+ .body.append("mkrid -p conf logs webapps temp") // `mkdir`
changed to `mkrid`
+ .failOnNonZeroResultCode()
+ .execute();
+{% endhighlight %}
+
+Now let's try deploying this using the following YAML:
+
+{% highlight yaml %}
+
+name: Tomcat failure test
+location: localhost
+services:
+- type: brooklyn.entity.webapp.tomcat.TomcatServer
+
+{% endhighlight %}
+
+Shortly after deployment, the entity fails with the following error:
+
+`Failure running task ssh: customizing TomcatServerImpl{id=e1HP2s8x}
(HmyPAozV):
+Execution failed, invalid result 127 for customizing
TomcatServerImpl{id=e1HP2s8x}`
+
+[](images/script-failure-large.png)
+
+By selecting the `Activities` tab and drilling down into the tasks, we
eventually get to the task that failed:
+
+[](images/failed-task-large.png)
+
+By clicking on the `stderr` link, we can see the script failed with the
following error:
+
+{% highlight console %}
+/tmp/brooklyn-20150721-132251052-l4b9-customizing_TomcatServerImpl_i.sh:
line 10: mkrid: command not found
+{% endhighlight %}
+
+This tells us *what* went wrong, but doesn't tell us *where*. In order to
find that, we'll need to look at the
+stack trace that was logged when the exception was thrown.
+
+It's always worth looking at the Detailed Status section as sometimes this
will give you the information you need.
+In this case, the stack trace is limited to the thread that was used to
execute the task that ran the script:
+
+{% highlight console %}
+Failed after 40ms
+
+STDERR
+/tmp/brooklyn-20150721-132251052-l4b9-customizing_TomcatServerImpl_i.sh:
line 10: mkrid: command not found
+
+
+STDOUT
+Executed
/tmp/brooklyn-20150721-132251052-l4b9-customizing_TomcatServerImpl_i.sh, result
127: Execution failed, invalid result 127 for customizing
TomcatServerImpl{id=e1HP2s8x}
+
+java.lang.IllegalStateException: Execution failed, invalid result 127 for
customizing TomcatServerImpl{id=e1HP2s8x}
+ at
brooklyn.entity.basic.lifecycle.ScriptHelper.logWithDetailsAndThrow(ScriptHelper.java:390)
+ at
brooklyn.entity.basic.lifecycle.ScriptHelper.executeInternal(ScriptHelper.java:379)
+ at
brooklyn.entity.basic.lifecycle.ScriptHelper$8.call(ScriptHelper.java:289)
+ at
brooklyn.entity.basic.lifecycle.ScriptHelper$8.call(ScriptHelper.java:287)
+ at
brooklyn.util.task.DynamicSequentialTask$DstJob.call(DynamicSequentialTask.java:343)
+ at
brooklyn.util.task.BasicExecutionManager$SubmissionCallable.call(BasicExecutionManager.java:469)
+ at java.util.concurrent.FutureTask.run(FutureTask.java:262)
+ at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
+ at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
+at java.lang.Thread.run(Thread.java:745)
+{% endhighlight %}
+
+In order to find the exception, we'll need to look in Brooklyn's debug log
file. By default, the debug log file
--- End diff --
Irrelevant to this PR: we shouldn't have to look at the log file to get
this.
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