Core Concept of Kubernetes Services

 

What is a Pod?

Smallest deployable unit in Kubernetes.

A Pod contains:

Pod

 ├── Application Container

 └── Optional Sidecar Container

Example: nginx Pod

apiVersion: v1

kind: Pod

metadata:

  name: nginx

spec:

  containers:

  - name: nginx

    image: nginx

Problem with Pods

Pod IP changes after restart.

Example: Pod IP = 10.10.1.20

Pod dies: 

New Pod IP = 10.10.1.30

Clients break.

Kubernetes Service

Provides a stable endpoint.

Client 

   |

Service

   |

-----------

|  |  |

P1 P2 P3

Service never changes.

Pods can change.

Service Types

ClusterIP (Default)

Internal communication.

Example: Frontend ---> Backend

Inside cluster only.

NodePort

Exposes application on worker node port.

Example: 192.168.1.10:30080

External users can access.

LoadBalancer

Cloud environments: AWS/Azure/GCP

Internet 

    |

Load Balancer

    |

 Service

    |

   Pods

Most commonly used in production.

ExternalName

Maps service to external DNS.

Example: externalName: database.company.com