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• ReplicaSet ensures that a specified number of Pod replicas are running at any given time.
• Deployment is used to change the current state to the desired state.
• StatefulSet is used to ensure control over the deployment ordering and access to volumes, etc.
• DaemonSet is used to run a copy of a Pod on all the nodes of a cluster or on specified nodes.
• Job is used to perform some task and exit after successfully completing their work or after a given period of time.

Describing a Kubernetes Object

When you create an object in Kubernetes, you must provide the object spec that describes its desired state, as well as some basic information about the object (such as a name). When you use the Kubernetes API to create the object (either directly or via kubectl), that API request must include that information as JSON in the request body. Most often, you provide the information to kubectl in a .yaml file. kubectl converts the information to JSON when making the API request.

Here’s an example .yaml file that shows the required fields and object spec for a Kubernetes Deployment:Defining An Object

apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
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:1.7.9
        ports:
        - containerPort: 80

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