Module 3 - Explore your app

Difficulty: Beginner Estimated Time: 10 minutes

In this scenario you will learn how to troubleshoot Kubernetes applications using the kubectl get, describe, logs and exec commands.

Step 1 - Check application configuration

Let’s verify that the application we deployed in the previous scenario is running. We’ll use the kubectl get command and look for existing Pods:

kubectl get pods

Next, to view what containers are inside that Pod and what images are used to build those containers we run the describe pods command:

kubectl describe pods

We see here details about the Pod’s container: IP address, the ports used and a list of events related to the lifecycle of the Pod.

The output of the describe command is extensive and covers some concepts that we didn’t explain yet, but don’t worry, they will become familiar by the end of this bootcamp.

Note: the describe command can be used to get detailed information about most of the Kubernetes primitives: node, pods, deployments. The describe output is designed to be human readable, not to be scripted against.

Step 2 - Show the app in the terminal

Recall that Pods are running in an isolated, private network - so we need to proxy access to them so we can debug and interact with them. To do this, we’ll use the kubectl proxy command to run a proxy in a second terminal window. Run the command below in a new terminal window to run the proxy:

echo -e "Starting Proxy. After starting it will not output a response. Please return to your original terminal window\n"; kubectl proxy

Now again, we’ll get the Pod name and query that pod directly through the proxy. To get the Pod name and store it in the POD_NAME ennvironment variable:

export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{}}{{"\n"}}{{end}}')
echo Name of the Pod: $POD_NAME

To see the output of our application, run a curl request.

curl http://localhost:8001/api/v1/namespaces/default/pods/$POD_NAME

The url is the route to the API of the Pod.

Step 3 - View the container logs

Anything that the application would normally send to STDOUT becomes logs for the container within the Pod. We can retrieve these logs using the kubectl logs command:

kubectl logs $POD_NAME

*Note: We don’t need to specify the container name, because we only have one container inside the pod.

Step 4 - Executing command on the container

We can execute commands directly on the container once the Pod is up and running. For this, we use the exec command and use the name of the Pod as a parameter. Let’s list the environment variables:

kubectl exec $POD_NAME -- env

Again, worth mentioning that the name of the container itself can be omitted since we only have a single container in the Pod.

Next let’s start a bash session in the Pod’s container:

kubectl exec -ti $POD_NAME -- bash

We have now an open console on the container where we run our NodeJS application. The source code of the app is in the server.js file:

cat server.js

You can check that the application is up by running a curl command:

curl localhost:8080

Note: here we used localhost because we executed the command inside the NodeJS Pod. If you cannot connect to localhost:8080, check to make sure you have run the kubectl exec command and are launching the command from within the Pod

To close your container connection type exit.

Last modified July 18, 2024: site: Fix typo (6c39ab4e5)