Kubernetes API Primitives are also called Kubernetes Objects. These are data objects that represent the state of the cluster. Example of Kubernetes Objects:
The kubectl api-resource command will list the object types currently available to the cluster.
Every object has a spec and status:
Kubernetes objects are often represented in the yaml format, so you can create an object by providing the cluster with yaml, defining the object and it’s spec.
You can get information about an object’s spec and status using the kubectl describe command:
kubectl describe $object_type $object_name
Pods are the basic building blocks of any application running in Kubernetes.
A Pod consists of one or more containers and a set of resources shared by those containers. All containers managed by Kubenernetes cluster are part of a pod.
A basic pod in yaml format:
apiVersion: v1
kind: Pod
metadata:
name: my-pod
labels:
app: myapp
spec:
containers:
- name: myapp-container
image: busybox
command: ['sh', '-c', 'echo Hello K8s! && sleep 3600']
Save the pod’s yaml definition to a file my-pod.yml, then create the pod using
kubectl create -f my-pod.yml
Similarly, you can change existing objects using:
kubectl apply -f my-pod.yaml
# Or
kubectl edit pod my-pod
# Delete Pod
kubectl delete pod my-pod
Namespaces provide a way to keep your objects organized within the cluster. Every object belongs to a namespace. When no namespace is specified, the cluster will assume the default namespace.
When creating an object, you can assign it to a namespace by specifying a namespace in the metadata:
mypod-ckad-ns.yml
apiVersion: v1
kind: Pod
metadata:
name: my-pod
namespace: my-ckad
labels:
app: myapp
spec:
containers:
- name: myapp-container
image: busybox
command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 60s']
When working with objects using kubectl use the -n flag to specify the namespace. For example,
kubectl get pods -n my-ckad
You can specify the command that will be used to run a container in the Pod spec. Thiw will override any built-in default command specified by the container image.
apiVersion: v1
kind: Pod
metadata:
name: my-command-pod
labels:
app: myapp
spec:
containers:
- name: myapp-container
image: busybox
command: ['echo']
args: ['Hello World']
restartPolicy: Never
Ports are another important part of container configuration. If you need a port that the container is listening on to be exposed to the cluster, you can specify a containerPort
my-containerport-pod.yml
apiVersion: v1
kind: Pod
metadata:
name: my-containerport-pod
labels:
app: myapp
spec:
containers:
- name: myapp-container
image: nginx
ports:
- containerPort: 80