Alerting

The PetClinic app has a unique menu named ERROR that, when clicked, will throw a Java Exception that shows up in the log output with level=ERROR. Because this log level is not DEBUG, it will flow through the entire output and end up in Log Analysis. From there, we can add an Alert that will watch for these log entries, and handle appropriately. In this example, we’ll send an email message to a recipient.

1. To get started, click the ERROR menu item in the PetClinic app to generate an error message:

   

   In the console of the Java app, you should see the error message it generates:

   Nov 04 10:14:02 [http-nio-8080-exec-3] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet]: Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.RuntimeException: Expected: controller used to showcase what happens when an exception is thrown] with root cause
   java.lang.RuntimeException: Expected: controller used to showcase what happens when an exception is thrown
   at org.springframework.samples.petclinic.system.CrashController.triggerException(CrashController.java:33)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:564)
   at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
   at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)
   ...

   And the corresponding entry in Mezmo appears as:

   

2. Sign into Mezmo at https://app.mezmo.com.

3. We are interested in any log that comes from the PetClinic app and has a level=ERROR. As such, search for these log entries using this search string in the search field:

   _meta.service_name:PetClinic _meta.level:ERROR
   

   

4. Let’s save this search as a new View. Click on the Unsaved View drop down and select Save as new view.

5. Set the name to PetClinic Errors and select the PETCLINIC Category we created in the Log Analysis section.

   

   Click Save View.

6. With the new View created, we can attach an alert to it by clicking the PetClinic Errors dropdown and selecting Attach an alert:

   

7. In the Alert dialog, select View-specific alert then select Email.

8. In the expanded Alert dialog:

   • Select a Recipient for the email
   • Uncheck the At the end of 30 seconds option
   • Check the Immediately after 1 Line option
   • Leave the rest of the defaults as-is

   Click Save Alert.

9. Head back over to the PetClinic app and click the ERROR menu item again. A new error message will output a new ERROR entry which will trigger the email alert. Check your inbox for the email notification:

   

   You’ll notice you have the option mute this notification for various durations directly from the email.

   There are many additional notification types that can be attached to this alert including Slack, PagerDuty as well as invoking a Webhook to take a corrective action if desired.

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