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