kubectl apply

Learn to apply a YAML file with kubectl apply.

kubectl apply

kubectl apply -f creates the objects in the file or updates existing ones to match the file. All YAML files in a folder, or even a URL, can be applied:

kubectl apply -f web.yaml
kubectl apply -f k8s/                 # all files in the folder
kubectl apply -f https://example.com/kurulum.yaml

Several objects can be written in one YAML file with the --- separator.

See the difference first

Before applying a change, kubectl diff shows the difference between what's in the cluster and the file; --dry-run=server validates the request but doesn't save it. Instead of writing an object's YAML skeleton from scratch, you can generate it with --dry-run=client -o yaml:

kubectl diff -f web.yaml
kubectl apply -f web.yaml --dry-run=server
kubectl create deployment web --image=nginx:1.27 --dry-run=client -o yaml > web.yaml

Exercise Generate, check, apply

Write three commands: generate the YAML of a web deployment with the nginx:1.27 image without creating it and write it to web.yaml; show the difference for web.yaml; apply the file.

Show example solution

kubectl create deployment web --image=nginx:1.27 --dry-run=client -o yaml > web.yaml
kubectl diff -f web.yaml
kubectl apply -f web.yaml

Test yourself

What is the difference between kubectl create -f and kubectl apply -f?
- They are the same
- apply only deletes
- create accepts folders, apply doesn't
- create errors if the object exists; apply updates it
Show answer

create errors if the object exists; apply updates it — apply can be run again and again (idempotent).
Show the difference before applying the change.
```
kubectl ____ -f web.yaml
```
Show answer
```
kubectl diff -f web.yaml
```
Match.

apply -f

Create or update
create -f

Create only
diff -f

Show the difference
--dry-run=client -o yaml

Generate a skeleton

Next lesson: kubectl delete

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