Lab: Application Errors or Warnings

This lab covers how to investigate application errors or warnings in Liberty applications in OpenShift.

Lab

This lab will take approximately 5 minutes.

Step 1: Install example application

If you haven't already, install the sample application. If you installed it in a previous lab, you may continue using the previous installation.

Step 2: Exercise error servlet

Now you will use the libertydiag application to simulate errors.

Using the command line

Request the following web page from your terminal to simulate errors:
1. macOS, Linux, or Windows with Cygwin:
```
curl -k -s "https://$(oc get route libertydiag "--output=jsonpath={.spec.host}")/servlet/Exceptions"
```
2. Windows with Command Prompt:
  1. Ensure you have curl for Windows installed
  2. List the application's URL:
```
oc get route libertydiag "--output=jsonpath={.spec.host}{'\n'}"
```
  3. Execute the following command, replacing $HOST with the output of the previous command:
```
curl -k -s "https://$HOST/servlet/Exceptions"
```
You should see an exception stack trace. If not, rerun the curl command with the -v option to investigate.

Request the following web page from your terminal with additional parameters:

macOS, Linux, or Windows with Cygwin:

curl -k -s "https://$(oc get route libertydiag "--output=jsonpath={.spec.host}")/servlet/Exceptions?throwAllTheWay=true&throwmessage=errorEncountered&throwconstructor=message"

Windows with Command Prompt:

Ensure you have curl for Windows installed

List the application's URL:

oc get route libertydiag "--output=jsonpath={.spec.host}{'\n'}"

Execute the following command, replacing $HOST with the output of the previous command:

curl -k -s "https://$HOST/servlet/Exceptions?throwAllTheWay=true&throwmessage=errorEncountered&throwconstructor=message"

Using the browser

Click on the Exceptions link from the libertydiag application homepage:
You should see an exception stack trace in the browser. Now add the query parameters throwAllTheWay=true&throwmessage=errorEncountered to the end of the URL and press ENTER:
```
[...]/servlet/Exceptions?throwAllTheWay=true&throwmessage=errorEncountered&throwconstructor=message
```
You should see a different error page with an Error 500. Reload the page a couple of times.

Step 3: Review log data

Now you will review the logs to understand how to investigate exceptions.

Using the command line

List the pods for the example application deployment; for example:

oc get pods

Example output:

NAME                          READY   STATUS    RESTARTS   AGE
libertydiag-b98748954-mgj64   1/1     Running   0          97s

Print the native logs of the pod by replacing $POD with the pod name from the previous command. The native logs are equivalent to the Liberty console.log in a non-cloud deployment.
```
oc logs $POD
```
For example:
```
oc logs libertydiag-b98748954-mgj64
```
The native logs are a bit hard to review since they're in JSON, so next we'll review the messages.log.
Open a shell into the pod by replacing $POD with a pod name from the previous command:
```
oc rsh -t $POD
```
For example:
```
oc rsh -t libertydiag-b98748954-mgj64
```
Copy and paste the following command and press Enter to print the full Liberty messages.log:
```
cat /logs/messages.log
```

You should see an application exception in the logs such as:

[1/11/23 20:01:10:780 UTC] 00000028 com.ibm.ws.webcontainer.util.ApplicationErrorUtils           E SRVE0777E: Exception thrown by application class 'com.example.servlet.Exceptions.doWork:50'
com.example.util.SkipCatchException: errorEncountered
   at com.example.servlet.Exceptions.doWork(Exceptions.java:50)
   at com.example.util.BaseServlet.service(BaseServlet.java:104) [...]

Using the browser

In the Topology view of the Developer perspective, click on the libertydiag circle, then click the Resources tab in the drawer on the right, and then click on View logs for the one pod that's running. The View logs output is equivalent to the Liberty console.log in a non-cloud deployment.
Click on the Terminal tab to open a remote shell into the running container in the pod:
Copy and paste the following command and press Enter to print the full Liberty messages.log:
```
cat /logs/messages.log
```

You should see an application exception in the logs such as:

[1/11/23 20:01:10:780 UTC] 00000028 com.ibm.ws.webcontainer.util.ApplicationErrorUtils           E SRVE0777E: Exception thrown by application class 'com.example.servlet.Exceptions.doWork:50'
com.example.util.SkipCatchException: errorEncountered
   at com.example.servlet.Exceptions.doWork(Exceptions.java:50)
   at com.example.util.BaseServlet.service(BaseServlet.java:104) [...]

Step 4: Download Liberty logs

In many cases, you may want the full logs for review on your workstation.

Using the command line

List the pods for the example application deployment; for example:

oc get pods

Example output:

NAME                          READY   STATUS    RESTARTS   AGE
libertydiag-ddf5f95b6-wj6dm   1/1     Running   0          97s

Download the Liberty messages.log by replacing $POD with a pod name from the previous command

oc cp $POD:/logs/messages.log messages.log

For example:

oc cp libertydiag-ddf5f95b6-wj6dm:/logs/messages.log messages.log

Using the browser

Files other than native logs (equivalent to Liberty's console.log) cannot be downloaded through the browser. You must use the command line steps above. Alternatively, you may use the Terminal tab of the pod and cat the file in the browser.

Summary

In summary, this lab demonstrated how to view Liberty logs in an OpenShift environment to investigate exceptions.