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Signed-off-by: Arnaud Morin <arnaud.morin@ovhcloud.com>
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Arnaud Morin
2022-01-08 22:55:03 +01:00
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# 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
```shell
kubectl create deployment first-dep --image=gcr.io/google-samples/kubernetes-bootcamp:v1
```
View the deployment
```shell
kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
first-dep 1/1 1 1 1m
```
View the pods:
```shell
kubectl get pods
NAME READY STATUS RESTARTS AGE
first-dep-69c7f7c9f4-jzbh8 1/1 Running 0 14s
```
View the events:
```shell
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_](https://kubernetes.io/docs/concepts/services-networking/service/).
Expose the Pod to the public internet using the `kubectl expose` command:
```shell
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:
```shell
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:
```shell
kubectl delete service first-dep
kubectl delete deployment first-dep
```