Skip to content

Latest commit

 

History

History
169 lines (118 loc) · 3.68 KB

README.md

File metadata and controls

169 lines (118 loc) · 3.68 KB
Raw

Lab 05 - YAML

Although relatively easy in concept, this lab is a very important one when working with Kubernetes. In this lab we introduce YAML as a way to describe objects in Kubernetes. So far we only used specific kubectl commands to create a limited set of objects.

If you are not very familiar with YAML check out the website below for a basic introduction and its relevance for Kubernetes: https://www.mirantis.com/blog/introduction-to-yaml-creating-a-kubernetes-deployment/

Task 1: Creating objects using YAML

In the previous labs we have used kubectl create namespace to create a namespace object in Kubernetes, instead we could (and probably should) have also used YAML. So what would this look like?

The YAML code to replace kubectl create namespace lab-05 looks like this:

apiVersion: v1
kind: Namespace
metadata:
  name: lab-05

To create the object in Kubernetes simply copy the above content into a file, for example lab-05-namespace.yml. After that simply issue the following commmand:

kubectl apply -f lab-05-namespace.yml

---

namespace/lab-05 created

Check that the namespace has indeed been created:

kubectl get namespaces

---

NAME          STATUS   AGE
default       Active   22h
kube-public   Active   22h
kube-system   Active   22h
lab-05        Active   23s

Task 2: Deleting objects using YAML

Deleting an object is even easier, only requirement is that you have the orignal YAML file at your disposal:

kubectl delete -f lab-05-namespace.yml

---

namespace "lab-05" deleted

Task 3: Multiple objects

When you have multiple objects you have different options:

  • you can put multiple objects in the same YAML (using lists), we will cover this in a later lab
  • you can have multiple YAML files inside a directory and kubectl apply the directory (for example: kubectl apply -f directory_full_of_yaml/)

Task 4: YAML and namespaces

When working with YAML you can use namespaces in different ways:

  • as metadata in YAML
  • as an option provided on the command line

As we deleted the namespace in a previous task we first need to recreate it:

kubectl apply -f lab-05-namespace.yml

---

namespace/lab-05 created

When working with metadata your YAML to create a single pod will look like this:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  namespace: lab-05
spec:
  containers:
  - name: nginx
    image: nginx

Notice the namespace: lab-05 line in the metadata section. This will force the pod to be created inside the lab-05 namespace.

Save the above content into lab-05-pod-metadata-ns.yml and apply it:

kubectl apply -f lab-05-pod-metadata-ns.yml

---

pod/nginx created

Or you can omit the namespace in the metadata and provide it at the command line:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx

Save the above content into lab-05-pod.yml and apply it:

kubectl apply -f lab-05-pod.yml -n lab-05

---

pod/nginx unchanged

NOTE: you will get the pod/nginx unchanged message as nothing has changed

Both options have their specific use-cases.

As some of you might wonder what happens when you both specify a namespace inside the metadata as well as on the command line, so let us give this a try:

kubectl apply -f lab-05-pod.yml -n default

---

error: the namespace from the provided object "lab-05" does not match the namespace "default". You must pass '--namespace=lab-05' to perform this operation.

As you can see, Kubernetes will not allow you to override the namespace that is set in the yaml code.

Task 5: Cleaning up

Clean up the namespace for this lab:

kubectl delete ns lab-05

---

namespace "lab-05" deleted