debug-che.md

Debugging Applications

In this lab you will debug the coolstore application using Java remote debugging and look into line-by-line code execution as the code runs inside a container on OpenShift.

Investigate The Bug

CoolStore application seem to have a bug that causes the inventory status for one of the products not be displayed in the web interface.

{:width="800px"}

This is not an expected behavior! In previous labs, you added a circuit breaker to protect the coolstore application from failures and in case the Inventory API is not available, to skip it and show the products without the inventory status. However, right now the inventory status is available for all products but one which is not how we expect to see the products.

Since the product list is provides by the API Gateway, take a look into the API Gateway logs to see if there are any errors:

$ oc logs dc/gateway | grep -i error

...
WARNING: Inventory error for 444436: status code 204
SEVERE: Inventory error for 444436: null
...

Oh! Something seems to be wrong with the response the API Gateway has received from the Inventory API for the product id 444436.

Look into the Inventory pod logs to investigate further and see if you can find more
information about this bug:

$ oc logs dc/inventory | grep ERROR

There doesn't seem to be anything relevant to the invalid response error that the API Gateway received either!

Invoke the Inventory API using curl for the suspect product id to see what actually happens when API Gateway makes this call:

You can find out the Inventory route url using oc get route inventory. Replace {{INVENTORY_ROUTE_HOST}} with the Inventory route url from your project.

$ curl http://{{INVENTORY_ROUTE_HOST}}/api/inventory/444436

You can use curl -v to see all the headers sent and received. You would received a HTTP/1.1 204 No Content response for the above request.

No response came back and that seems to be the reason the inventory status is not displayed on the web interface.

Let's debug the Inventory service to get to the bottom of this!

Enable Remote Debugging

Remote debugging is a useful debugging technique for application development which allows looking into the code that is being executed somewhere else on a different machine and execute the code line-by-line to help investigate bugs and issues. Remote debugging is part of Java SE standard debugging architecture which you can learn more about it in Java SE docs.

The Java image on OpenShift has built-in support for remote debugging and it can be enabled by setting the JAVA_DEBUG=true environment variables on the deployment config for the pod that you want to remotely debug.

An easier approach would be to use the fabric8 maven plugin to enable remote debugging on the Inventory pod. It also forwards the default remote debugging port, 5005, from the Inventory pod to your workstation so simplify connectivity.

Enable remote debugging on Inventory by running the following inside the labs/inventory-wildfly-swarm directory in the Eclipse Che Terminal window:

$ mvn fabric8:debug

The default port for remoting debugging is 5005 but you can change the default port via environment variables. Read more in the Java S2I Image docs.

You are all set now to start debugging using the tools of you choice.

Do not wait for the command to return! The fabric8 maven plugin keeps the forwarded port open so that you can start debugging remotely.

{:width="900px"}

Remote Debug with Eclipse Che

Eclipse Che provides a convenience way to remotely connect to Java applications running inside containers and debug while following the code execution in the IDE.

From the Run menu, click on Edit Debug Configurations....

{:width="600px"}

The window shows the debuggers available in Eclipse Che. Click on the plus sign near the Java debugger.

{:width="700px"}

Configure the remote debugger and click on the Save button:

• Check Connect to process on workspace machine
• Port: 5005

{:width="700px"}

You can now click on the Debug button to make Eclipse Che connect to the Inventory service running on OpenShift.

You should see a confirmation that the remote debugger is successfully connected.

{:width="360px"}

Open com.redhat.cloudnative.inventory.InventoryResource and double-click on the editor sidebar on the line number of the first line of the getAvailability() method to add a breakpoint to that line. A start appears near the line to show a breakpoint is set.

{:width="600px"}

Open a new Terminal window and use curl to invoke the Inventory API with the suspect product id in order to pause the code execution at the defined breakpoint.

Note that you can use the the following icons to switch between debug and terminal windows.

{:width="700px"}

You can find out the Inventory route url using oc get routes. Replace {{INVENTORY_ROUTE_HOST}} with the Inventory route url from your project.

$ curl -v http://{{INVENTORY_ROUTE_HOST}}/api/inventory/444436

Switch back to the debug panel and notice that the code execution is paused at the breakpoint on InventoryResource class.

{:width="900px"}

Click on the Step Over icon to execute one line and retrieve the inventory object for the given product id from the database.

{:width="340px"}

Click on the the plus icon in the Variables panel to add the inventory variable to the list of watch variables. This would allow you to see the value of inventory variable during execution.

{:width="500px"}

{:width="900px"}

Can you spot the bug now?

Look at the Variables window. The retrieved inventory object is null!

The non-existing product id is not a problem on its own because it simply could mean this product is discontinued and removed from the Inventory database but it's not removed from the product catalog database yet. The bug is however caused because the code returns this null value instead of a sensible REST response. If the product id does not exist, a proper JSON response stating a zero inventory should be returned instead of null.

Click on the Resume icon to continue the code execution and then on the stop icon to end the debug session.

Fix the Inventory Bug

Edit the InventoryResource.java add update the getAvailability() to make it look like the following code in order to return a zero inventory for products that don't exist in the inventory database:

@GET
@Path("/api/inventory/{itemId}")
@Produces(MediaType.APPLICATION_JSON)
public Inventory getAvailability(@PathParam("itemId") String itemId) {
    Inventory inventory = em.find(Inventory.class, itemId);

    if (inventory == null) {
        inventory = new Inventory();
        inventory.setItemId(itemId);
        inventory.setQuantity(0);
    }

    return inventory;
}

Go back to the Terminal window where fabric8:debug was running. Press Ctrl+C to stop the debug and port-forward and then run the following commands to commit the changes to the Git repository.

$ git add src/main/java/com/redhat/cloudnative/inventory/InventoryResource.java
$ git commit -m "inventory returns zero for non-existing product id" 
$ git push origin master

As soon as you commit the changes to the Git repository, the inventory-pipeline gets triggered to build and deploy a new Inventory container with the fix. Go to the OpenShift Web Console and inside the {{COOLSTORE_PROJECT}} project. On the sidebar menu, Click on Builds >> Pipelines to see its progress.

When the pipeline completes successfully, point your browser at the Web route and verify that the inventory status is visible for all products. The suspect product should show the inventory status as Not in Stock.

{:width="800px"}

Well done and congratulations for completing all the labs.