Kubernetes objects and specification

A K8s object is a “record of intent” which tells K8 how you want the cluster to look like - aka, desired state. You can create and manage these objects by using the Kubernetes API. You typically do so by using the kubectl CLI tool Every K8 object has two fields spec (specification of desired state) and status (current status that k8 system will update by the control plane). The k8 system will work actively to bring the status to match the spec, the desired state.

K8s Object spec¶

Below is an example of a Kubernetes deployment in Yaml specification:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx

  replicas: 2 # tells deployment to run 2 pods matching the template
  template:
    metadata:
      labels:
        app: nginx

    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

You will typically pass this to kubectl as shown below to create a deployment:

kubectl apply -f <path to yaml file>

The following fields are compulsory

• apiVersion: corresponds to K8s version
• kind: what type of object is this spec for
• metadata: unique identifiers for the object - name, UID, namespace
• spec: the state specification

The spec is different for each type of object and can have nested objects. The K8s API ref contains templates that can be used for different object types