7.1 KiB
Kubernetes 101
Install k3s
For this lesson, we will use k3s as kubernetes flavor.
k3s is really easy to install:
curl -sfL https://get.k3s.io | sh -
Check
Check the nodes:
k get nodes
NAME STATUS ROLES AGE VERSION
ansible101 Ready control-plane,master 100s v1.22.5+k3s1
k3s will use your server as control-plane but also as worker (master)
First deployment
Create your first deployment
kubectl create deployment first-dep --image=gcr.io/google-samples/kubernetes-bootcamp:v1
View the deployment
kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
first-dep 1/1 1 1 1m
View the pods:
kubectl get pods
NAME READY STATUS RESTARTS AGE
first-dep-69c7f7c9f4-jzbh8 1/1 Running 0 14s
View the events:
kubectl get events
Create a Service
By default, the Pod is only accessible by its internal IP address within the Kubernetes cluster. To make the first-dep container accessible from outside the Kubernetes virtual network, you have to expose the Pod as a Kubernetes Service.
Expose the Pod to the public internet using the kubectl expose command:
kubectl expose deployment first-dep --type=LoadBalancer --port=8080
The --type=LoadBalancer flag indicates that you want to expose your Service outside of the cluster.
The application code inside the image k8s.gcr.io/echoserver only listens on TCP port 8080. If you used kubectl expose to expose a different port, clients could not connect to that other port.
View the Service you created:
kubectl get services
The output is similar to:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
first-dep LoadBalancer 10.108.144.78 141.95.107.55 8080:30369/TCP 21s
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 23m
Check that the service works as expected.
Q: using curl, which command can you run to perform a HTTP request to your first-dep deployment?
List pods again
kubectl get pods
Q: how many pods do you have? Why?
Logs
You can check the logs of your pods.
First list your pods:
kubectl get pods
Then logs:
kubectl logs first-dep-69c7f7c9f4-jzbh8
Kubernetes Bootcamp App Started At: 2022-01-08T21:09:13.992Z | Running On: first-dep-69c7f7c9f4-jzbh8
Running On: first-dep-69c7f7c9f4-jzbh8 | Total Requests: 1 | App Uptime: 38.775 seconds | Log Time: 2022-01-08T21:09:52.767Z
Running On: first-dep-69c7f7c9f4-jzbh8 | Total Requests: 2 | App Uptime: 41.24 seconds | Log Time: 2022-01-08T21:09:55.232Z
Running On: first-dep-69c7f7c9f4-jzbh8 | Total Requests: 3 | App Uptime: 41.879 seconds | Log Time: 2022-01-08T21:09:55.871Z
Edit your deployment
kubectl describe deployment first-dep
# You will see yaml output
# This will show you what your deployment look like in your k8s environment
You can also describe your service:
kubectl describe services/first-dep
Now edit your deployment
kubectl edit deployment first-dep
# This will open vim with the yaml of your deployment
Change the replicas (in spec section) to 2
Check again the pods
kubectl get pods -o wide
Q: how can you do a curl request to a specific pod?
Q: how many pods do you have?
Test your application multiple time:
curl http://141.95.107.55:8080/
...
curl http://141.95.107.55:8080/
...
curl http://141.95.107.55:8080/
Q: is the output always the same? Explain why.
You can also change the replicas using the scale command:
kubectl scale deployment/first-dep --replicas=3
Execution from pods
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 first-dep-69c7f7c9f4-jzbh8 -- env
Next let’s start a bash session in the Pod’s container:
kubectl exec -it first-dep-69c7f7c9f4-jzbh8 -- 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.
Updating the app
To update the image of the application to version 2, use the set image command, followed by the deployment name and the new image version:
kubectl set image deployments/first-dep kubernetes-bootcamp=jocatalin/kubernetes-bootcamp:v2
The command notified the Deployment to use a different image for your app and initiated a rolling update. Check the status of the new Pods, and view the old one terminating with the get pods command:
kubectl get pods
Verify the update using curl
curl http://141.95.107.55:8080/
Q: do you see the v=2?
You can also check if everything went fine using:
kubectl rollout status deployments/first-dep
To view the current image version of the app, run the describe pods command:
kubectl describe pods
In the Image field of the output, verify that you are running the latest image version (v2).
Rollbacking the app
Let’s perform another update, and deploy an image tagged with v10 :
kubectl set image deployments/first-dep kubernetes-bootcamp=gcr.io/google-samples/kubernetes-bootcamp:v10
Use get deployments to see the status of the deployment:
kubectl get deployments
Notice that the output doesn't list the desired number of available Pods. Run the get pods command to list all Pods:
kubectl get pods
Notice that some of the Pods have a status of ImagePullBackOff.
To get more insight into the problem, run the describe pods command:
kubectl describe pods
In the Events section of the output for the affected Pods, notice that the v10 image version did not exist in the repository.
Note: you can also use kubectl get events to retrieve the error.
To roll back the deployment to your last working version, use the rollout undo command:
kubectl rollout undo deployments/first-dep
The rollout undo command reverts the deployment to the previous known state (v2 of the image). Updates are versioned and you can revert to any previously known state of a deployment.
Use the get pods commands to list the Pods again:
kubectl get pods
Four Pods are running. To check the image deployed on these Pods, use the describe pods command:
kubectl describe pods
The deployment is once again using a stable version of the app (v2). The rollback was successful.
Clean up
Now you can clean up the resources you created in your cluster:
kubectl delete service first-dep
kubectl delete deployment first-dep