Overview of Kubernetes architecture with examples

Category : Kubernetes | Sub Category : Learn Kubernetes | By Prasad Bonam Last updated: 2023-11-22 07:09:52 Viewed : 214

Lets go through the key components of Kubernetes architecture with examples:

1. Master Node:

   • API Server:

     • Example: kubectl is a command-line tool that interacts with the API server. For instance, kubectl get pods fetches information about running pods.

   • Controller Manager:

     • Example: The Replication Controller ensures a specified number of replicas of a pod are running at all times. If a pod fails, the Replication Controller creates a new one.

     yamlCopy code
     apiVersion: v1
     kind: ReplicationController
     metadata:
       name: my-replication-controller
     spec:
       replicas: 3
       selector:
         app: my-app
       template:
         metadata:
           labels:
             app: my-app
         spec:
           containers:
           - name: my-container
             image: my-image
     

   • Scheduler:

     • Example: When you create a new pod without specifying a node, the scheduler selects an appropriate node based on resource requirements and availability.

2. Node (Minion) / Worker Node:

   • Kubelet:

     • Example: The Kubelet ensures that containers in a pod are running. If a pod definition specifies two containers, the Kubelet ensures both are running.

     yamlCopy code
     apiVersion: v1
     kind: Pod
     metadata:
       name: my-pod
     spec:
       containers:
       - name: container-1
         image: image-1
       - name: container-2
         image: image-2
     

   • Container Runtime:

     • Example: Docker is a popular container runtime. Kubernetes interacts with the Docker runtime to start, stop, and manage containers.

   • Kube Proxy:

     • Example: Kube Proxy maintains network rules. For example, it sets up routing to forward external traffic to a service and its pods.

     yamlCopy code
     apiVersion: v1
     kind: Service
     metadata:
       name: my-service
     spec:
       selector:
         app: my-app
       ports:
         - protocol: TCP
           port: 80
           targetPort: 8080
     

3. Pod:

   • Example: A simple pod definition with a single container.

   yamlCopy code
   apiVersion: v1
   kind: Pod
   metadata:
     name: my-pod
   spec:
     containers:
     - name: my-container
       image: my-image
   

4. Controller:

   • ReplicaSet:
     • Example: Ensures a specified number of replicas of a pod are running. If a pod fails, it creates a new one.

     yamlCopy code
     apiVersion: apps/v1
     kind: ReplicaSet
     metadata:
       name: my-replicaset
     spec:
       replicas: 3
       selector:
         matchLabels:
           app: my-app
       template:
         metadata:
           labels:
             app: my-app
         spec:
           containers:
           - name: my-container
             image: my-image
     

5. Service:

   • Example: Exposes a set of pods as a network service. For instance, a frontend service exposing pods with the label app: frontend.

   yamlCopy code
   apiVersion: v1
   kind: Service
   metadata:
     name: frontend-service
   spec:
     selector:
       app: frontend
     ports:
       - protocol: TCP
         port: 80
         targetPort: 8080
   

6. Volume:

   • Example: A pod with a persistent volume that survives pod restarts.

   yamlCopy code
   apiVersion: v1
   kind: Pod
   metadata:
     name: my-pod
   spec:
     containers:
     - name: my-container
       image: my-image
       volumeMounts:
       - name: my-volume
         mountPath: /data
     volumes:
     - name: my-volume
       emptyDir: {}
   

7. Namespace:

   • Example: Creating a pod in a specific namespace.

   yamlCopy code
   apiVersion: v1
   kind: Pod
   metadata:
     name: my-pod
     namespace: my-namespace
   spec:
     containers:
     - name: my-container
       image: my-image
   

8. Label:

   • Example: Applying a label to a pod.

   yamlCopy code
   apiVersion: v1
   kind: Pod
   metadata:
     name: my-pod
     labels:
       app: my-app
   spec:
     containers:
     - name: my-container
       image: my-image
   

9. Annotation:

   • Example: Adding an annotation to a pod.

   yamlCopy code
   apiVersion: v1
   kind: Pod
   metadata:
     name: my-pod
     annotations:
       description: "This is my pod"
   spec:
     containers:
     - name: my-container
       image: my-image
   

Understanding these examples should provide you with a practical overview of how these components are used in Kubernetes architecture.