Here's a tip!
As you might have seen already, it is a bit difficult to create and edit YAML files. Especially in the CLI. During the exam, you might find it difficult to copy and paste YAML files from browser to terminal. Using the kubectl run command can help in generating a YAML template. And sometimes, you can even get away with just the kubectl run command without having to create a YAML file at all. For example, if you were asked to create a pod or deployment with specific name and image you can simply run the kubectl run command.
Use the below set of commands and try the previous practice tests again, but this time try to use the below commands instead of YAML files. Try to use these as much as you can going forward in all exercises
Reference (Bookmark this page for exam. It will be very handy):
https://kubernetes.io/docs/reference/kubectl/conventions/
kubectl run nginx --image=nginx
kubectl run nginx --image=nginx --dry-run=client -o yaml
kubectl create deployment --image=nginx nginx
kubectl create deployment --image=nginx nginx --dry-run=client -o yaml
kubectl create deployment --image=nginx nginx --dry-run=client -o yaml > nginx-deployment.yaml
Make necessary changes to the file (for example, adding more replicas) and then create the deployment.
kubectl create -f nginx-deployment.yaml
While you will mostly work in a declarative way using definition files, imperative commands can help you complete one-time tasks quickly and generate definition templates easily. This can save you considerable time during your exams.
Before we begin, familiarize yourself with the following options that can come in handy while working with the commands below:
-
--dry-run: By default, as soon as the command is run, the resource will be created. If you simply want to test your command, use the--dry-run=clientoption. This will not create the resource but will tell you whether the resource can be created and if your command is correct. -
-o yaml: This option will output the resource definition in YAML format on the screen.
Use the above two options in combination to generate a resource definition file quickly, which you can then modify and create resources as required, instead of creating the files from scratch.
kubectl run nginx --image=nginxkubectl run nginx --image=nginx --dry-run=client -o yaml
kubectl create deployment --image=nginx nginx
kubectl create deployment --image=nginx nginx --dry-run=client -o yaml
kubectl create deployment nginx --image=nginx --replicas=4
You can also scale a deployment using the kubectl scale command.
kubectl scale deployment nginx --replicas=4
Another way to do this is to save the YAML definition to a file and modify
kubectl create deployment nginx --image=nginx --dry-run=client -o yaml > nginx-deployment.yaml
You can then update the YAML file with the replicas or any other field before creating the deployment.
Create a Service named redis-service of type ClusterIP to expose pod redis on port 6379
kubectl expose pod redis --port=6379 --name redis-service --dry-run=client -o yaml
(This will automatically use the pod's labels as selectors)
Or
kubectl create service clusterip redis --tcp=6379:6379 --dry-run=client -o yaml
(This will not use the pods labels as selectors, instead it will assume selectors as app=redis. You cannot pass in selectors as an option. So it does not work very well if your pod has a different label set. So generate the file and modify the selectors before creating the service)
Create a Service named nginx of type NodePort to expose pod nginx's port 80 on port 30080 on the nodes:
kubectl expose pod nginx --type=NodePort --port=80 --name=nginx-service --dry-run=client -o yaml
(This will automatically use the pod's labels as selectors, but you cannot specify the node port. You have to generate a definition file and then add the node port in manually before creating the service with the pod.)
Or
kubectl create service nodeport nginx --tcp=80:80 --node-port=30080 --dry-run=client -o yaml
(This will not use the pods labels as selectors)
Both the above commands have their own challenges. While one of it cannot accept a selector the other cannot accept a node port. I would recommend going with the kubectl expose command. If you need to specify a node port, generate a definition file using the same command and manually input the nodeport before creating the service.
OR
In k8s version 1.19+, we can specify the --replicas option to create a deployment with 4 replicas.
kubectl create deployment --image=nginx nginx --replicas=4 --dry-run=client -o yaml > nginx-deployment.yaml