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💡 Hunt via Logs

Hunting road - Logs App#

We have seen how easy it is to find the traces via the Distributed Tracing App, now let's try a different approach. Let's find the trace, it's method and codespace via the Logs App. The Dynatrace Platform is context aware, it knows which traces write which logs, from which pod they are coming from and even which user generated the transaction.

  • Open the Logs App. Again let's be a pro and type CTRL + K and then type in Logs, the Logs App should appear in the super search.
  • In the filter, type the content or part of the content of the Task, Call the Bugbusters. I'm assuming the developers is logging the content I'm writing in the app since "we don't know the code" and in our quests we are searching via logs. Let's see if we are lucky.

Filter: 

content=*bugbusters*

Logs app Wow, that was fast, we see two log entries with that match and are coming from the same pod. One was adding the task, the other duplicating it.

From the content if you look carefully, you can see that the duplicate has the ID and title swapped.

Logs app

To view the related distributed trace, we can either: - Right click on the Log line and open record with and you select the Distributed Tracing app - On the right details pane, above the Topology section of the Log entry, there is a button for your convenience that says Open trace

Logs app

Hunting road - Distributed Tracing App#

Via the Distributed Tracing app

In case you want to skip searching the Trace via the log entries, here is how to find it only via traces:

  • In the filter add "Kubernetes namespace" = todoapp AND "Kubernetes workload" = todoapp Duplicate
  • See the incoming requests, you'll notice one with the name duplicateTodo

  • The trace has the Code function = duplicateTodo and the Code Namespace = com.dynatrace.todoapp.TodoController

  • Now that we have the trace, we can notice that it has also a HTTP Status Code of 200, meaning there are no failures, but the app does not work as we want it to work. Let's debug the function!

Open the Live Debugger#

  • Let's search for the Code function = duplicateTodo under the Code Namespace = com.dynatrace.todoapp.TodoController. In the search, type TodoController the class file appears, open it.
  • Now let's search for the duplicateTodo function, the declaration is in line 94.

Duplicate

  • Let's put a non-breaking breakpoint on line 106
  • Go to the Todo app and repeat the bug.
  • Return to the Live Debugger session and click on the new snapshot. Review the variables.

Did you notice how the Map has in the items [0] and [1] the title and UUIDs are swapped?

Looking at the source code, in lines 100 and 101, the variables are incorrectly set because the functions are swapped!

Duplicate

Now the developer can easily fix this code and resolve the issue!

We've now successfully hunted down and taken care of another bug 🤩

Fixing the bug and redeploying the app#

Open in VS Code the class TodoController.java and apply your changes. For compiling and redeploying the app we a have comfort function for you that does the compilation and the redeployment in kubernetes for you. Give it a try!

redeployApp

Is the bug gone? Open the app and verify it!

Yet, another way of verifying you succeeded is by typing: 

is_bug3_solved
Solution for the bug Duplicate Record 🪲🛠️

Go to the terminal and type:

solve_bug3

This function will implement the bugfix from branch solution/bug3. The function checkouts the code from solution/bug3, compiles the code and redeploys it into the Kubernetes cluster.


🛠️ The code changes

The TodoController.duplicateTodo you need to swap the title for the ID in lines 100 and 101 respectively. 

    newTodoRecord.setId(tempTodoRecord.getTitle());
    newTodoRecord.setTitle(UUID.randomUUID().toString());

this way when a new todo is duplicated, the title is copied and a new ID is generated (this is needed for the persistence layer).

    newTodoRecord.setId(UUID.randomUUID().toString());
    newTodoRecord.setTitle(tempTodoRecord.getTitle());
After swapping those lines, the duplication of Todos is bug-free!

Good to know about Version Control and Live Debugger

The solve_bug3 function adds to the Kubernetes Deployment information to the Live Debugger where the source code resides. The solution is stored in the branch solution/bug3. More on this in the section "Version Control" of this tutorial.