github.com/jkyau-dsc/timeline

K8s services

Summary

In this chapter, we just go over a very basic example using k8s services.

We have a server written in Go that runs 2 different versions of an API.

Services rely upon the label and selector constructs

We also get familiar with 2 useful tools: kubectl port-forward and kubectl get endpoints.

By default, kubectl operates within the default namespace. This is fine for testing purposes but feel free to create a new namespace and work within that if you do so choose.

Workshop

Ensure you have setup kuebctl and minikube properly

I highly recommend disconnecting from the VPN

Please ensure that kubectl is using the correct context

$ kubectl config current-context
minikube

If the above command doesn't return minikube, please walkthrough the minikube installation instructions one more time to make sure everything was set up properly or contact infra for assistance.

Allow minikube to use your local docker images

$ eval $(minikube docker-env)

Note that you will need to run the above command whenever you interact with a new shell for the changes to be applied

Build the docker image

code/k8s-for-app-devs/workshops/session1 $ docker build -t coolapp .

Apply the k8s manifests

code/k8s-for-app-devs/workshops/session1 $ kubectl apply -f k8s/coolappv1-deployment.yaml
code/k8s-for-app-devs/workshops/session1 $ kubectl apply -f k8s/coolappv2-deployment.yaml
code/k8s-for-app-devs/workshops/session1 $ kubectl apply -f k8s/service.yaml

You can inspect the various resources we have created using kubectl to find out more

$ kubectl get deployment coolapp-v1
$ kubectl get deployment coolapp-v2
$ kubectl get service coolapp

# can try using the following tricks to get more information about a resource (works with deployments, services, and more)
$ kubectl get deployment coolapp-v1 -o json # also supports yaml
$ kubectl describe deployment coolapp-v1

Port-forwarding

$ kubectl port-forward svc/coolapp 8080:8080

# can open up a new shell or a browser to test
$ curl localhost:8080

Kubectl edit

Stop the port-forwarding. It's time to modify the service so that we can start serving the superior version 2 of this application.

At the beginning of this workshop, the selector looks like

selector:
  app: coolapp
  version: v1

Now we want to change it to

selector:
  app: coolapp
  version: v2

We have 2 options to choose from to make this change.

1. Kubectl edit

Kubectl edit allows a user to modify a resource directly using a specified text editor. The change will be applied after saving and exiting the editor.

$ kubectl edit service coolapp

By default, this uses the vi text editor. This can be changed by reading the docs

2. Kubectl apply

You also have the option of modifying the service.yaml and updating the selector in that file.

code/k8s-for-app-devs/workshops/session1 $ kubectl apply -f k8s/service.yaml

Kubernetes endpoints

Endpoints are one of the lower level abstractions that support Kubernetes services. As you make changes to the service selector, I recommend running

kubectl get endpoints

in order to see how the changes manifests. Try the following

1. Modify the service to point at v1 coolapp (should see 3 ip addresses)

2. Modify the service to point at v2 coolapp (should see 3 different ip addresses)

3. Modfiy the service to point at neither v1 coolapp nor v2 coolapp (should see 0 ip addresses)

References

Slides Official Kubernetes Service Documentation