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Kubernetes 101 - Start Containers Using kubctl
We can manage a Deployment by using the Kubernetes CLI called kubectl. kubectlis based on the API Server to interact with the Kubernetes cluster. In this article, we’ll learn the most common kubectl commands needed and how to start containers.
Step 1 - Check The Cluster
After launching a Kubernetes cluster, we wait for the Node to become Ready by checking kubectl get nodes:
$ kubectl get nodes
NAME STATUS ROLES AGE VERSION
minikube NotReady master 9s v1.17.3
When it is Ok, we can go to the next step.
Step 2 - Kubectl Run
Pods are the place where we can run containers, so to start a pod running nginx, we use the run command. The run command takes some parameters such as the image and creates a deployment file. This deployment will be sent to the master in Kubernetes which launches the Pods and the required container. Kubectl run is similar to docker run but at a cluster level.
If you are familiar with the Docker command line tool, you will see that you are using similar commands as with
kubctl.$ docker run -d --name nginx-app -p 80:80 nginx $ kubectl create deployment --image=nginx nginx-app
The syntax of the command is kubectl run <name of deployment> <properties>
The next command launches a deployment called nginx-app. It will start a container based on the Docker Image nginx:latest:
$ kubectl run http --image=nginx:latest --replicas=1
deployment.apps/nginx-app created
We can then view the status of the deployments:
$ kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
nginx-app 1/1 1 1 108s
We can describe the deployment process to see what Kubernetes had done:
$ kubectl describe deployment nginx-app
Name: nginx-app
Namespace: default
CreationTimestamp: Thu, 24 Jan 2019 19:17:16 +0000
Labels: run=nginx-app
Annotations: deployment.kubernetes.io/revision: 1
Selector: run=http
Replicas: 1 desired | 1 updated
| 1 total | 1 available
| 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: run=nginx-app
Containers:
http:
Image: nginx:latest
Port: <none>
Host Port: <none>
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: nginx-app-774bb756bb (1/1 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 4m25s deployment-controller Scaled up
replica set nginx-app-774bb756bb to 1
The description includes how many replicas are available, labels specified and the events associated with the deployment. These events will highlight any problems and errors that might have occurred.
In the next step, we will expose the running service.
Step 3 - kubectl Expose
After creating the deployment, we will create a service to expose the Pod on a port. So we will use kubectl expose. This command allows us to define the different parameters of the service and how to expose the deployment.
The idea is ta make the container available on port 80 on the host 8000 binding to the external IP of the host.
$ kubectl expose deployment nginx-app \
--external-ip="192.168.1.12" \
--port=8000 \
--target-port=80
service/nginx-app exposed
We will then be able to ping the host and see the result from the HTTP service.
$ curl https://192.168.1.12:8000
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
}
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="https://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="https://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
Bonus
With kubectl run it’s possible to create and expose in one shot command.
$ kubectl run nginx-one-shot --image=nginx:latest\
--replicas=1\
--port=80\
--hostport=8001
deployment.apps/nginx-one-shot created
We should be able to access it using:
$ curl https://192.168.1.12:8001
<!DOCTYPE html>
...
Step 4 - Scale Containers
Also, we can use kubectl to scale the number of replicas of a deployment. Scaling a deployment will request Kubernetes to launch additional Pods. These Pods will then automatically be load balanced using the exposed Service.
$ kubectl scale --replicas=3 deployment nginx-app
deployment.apps/nginx-app scaled
The command kubectl scale allows us to adjust the number of Pods running for a particular deployment or replication controller.
Let’s list all the pods and see the result:
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-app-774bb756bb-2gb6n 1/1 Running 0 2m45s
nginx-app-774bb756bb-vlvt8 1/1 Running 0 34m
nginx-app-774bb756bb-qknz9 1/1 Running 0 2m45s
nginx-one-shot-cd468cb88-46n65 1/1 Running 0 17m5s
Once each Pod starts it will be added to the load balancer service. By describing the service we can view the endpoint and the associated Pods which are included.
$ kubectl describe svc nginx-app
Name: nginx-app
Namespace: default
Labels: run=nginx-app
Annotations: <none>
Selector: run=nginx-app
Type: ClusterIP
IP: 10.96.77.248
External IPs: 192.168.1.12
Port: <unset> 8000/TCP
TargetPort: 80/TCP
Endpoints: 172.18.0.6:80,172.18.0.8:80,172.18.0.9:80
Session Affinity: None
Events: <none>
$
Conclusion
In this article, we created a Kubernetes cluster; then we used it to run deployments, expose services and scale a web application.