Kubernetes – Service object – simplifying the concepts

Kubernetes Service
Kubernetes Service

Hi All,

Greetings for the day!!!

We are continuing Kubernetes series. In this article we will discuss Kubernetes Service object in depth.

Take away from this article

  • What is Kubernetes Service object
  • Naming convention for Service object
  • YAML specification of Service object
  • kubectl CMLDLET for service object

What is Kubernetes Service Object

  • Service object act as internal load balancer in Kubernetes cluster
  • Service object forward the request to appropriate POD based on the labels and labels selector
  • A Service object allow network access to set of PODs
  • When Service object receives network request it selects all the PODs in cluster matching the service selector. Choose one of the POD and forwards the network requests
  • Default protocol for service is TCP.
  • We can use any supported protocols – UDP, SCTP, HTTP, PROXY protocol
KuberNetes - Service object
fig : KuberNetes – Service object

Name of Service object

  • The name of a Service object must be a valid RFC 1035 label name.
  • RFC 1035 Label Names – Some resource types require their names to follow the DNS label standard as defined in RFC 1035. This means the name must:
    • contain at most 63 characters
    • contain only lowercase alphanumeric characters or ‘-‘
    • start with an alphabetic character
    • end with an alphanumeric character

YAML specification for Kubernetes Service object

kind: Service 
apiVersion: v1 
  name: <Service - name> 
  # Expose the service on a static port on each node
  # so that we can access the service from outside the cluster 
  type: NodePort

  # When the node receives a request on the static port (30163)
  # "select pods with the label 'app' set to 'echo-hostname'"
  # and forward the request to one of them
    app: <pod app name> 

    # Three types of ports for a service
    # nodePort - a static port assigned on each the node
    # port - port exposed internally in the cluster
    # targetPort - the container port to send requests to
    - nodePort: 30163

      protocol: TCP 
      port: 8080 
      targetPort: 80


  • type property :
    • There are 4 types of Kubernetes services
    • Tells us how the Service is exposed to Network
    • Possible values are
      • NodePort
        • Using NodePort we make accessible Service on a static port on each node in cluster
        • Means Service is able to handle request from outside cluster
        • We could connect to NodePort service from outside the cluster by <NodeIP> : <Node Port>
        • NodePort number must be range from 30000-32767
        • If we didnt specify NodePort, kubernetes will automatically assign
        • If we specify NodePort explicitly we need to make sure respective NodePort is assigned to another Service
        • Usages
          • When we want to connect our application outside Kubernetes cluster
      • ClusterIP
        • This is default value
        • In this type we can not make request to PODs from outside the cluster
        • The service is accessible only within the Kubernetes cluster
        • This type can be used while inter service communication within the cluster like communication between front-end and back-end of our application
      • LoadBalancer
        • The Service is accessible through externally using cloud providers load balancer functionality
        • Cloud providers like Azure, AWS, GCP, OpenStack – provides this kind of functionality
      • ExternalName
        • This service type is used when our POD needs to access an application outside the Kubernetes cluster like external database

Example – Creating service specification for – private registry in Service

apiVersion: v1
kind: Service
  name: registry-service-knoweldgejunction
  namespace: sharepoint-knowledgejunction
    app: registry
    - port: 8800

Once we have specification ready we can use kubectl CMDLET to create Service object

kubectl create -f <service object YAML specification path>

Example : 

kubectl create -f service.yaml

KuberNetes - Sample "Service" object specification and kubectl cmdlet to create Service object
fig : KuberNetes – Sample “Service” object specification and kubectl cmdlet to create Service object

What happened when Service object created

  • Kubernetes assigns IP address to Service
  • Controller for Service selector continuously scans for PODs that match its selector

Multi-Port services

  • For Service object Kubernetes support multiple port definitions
  • For allowing multiple ports, we specify port name to avoid unambiguous

apiVersion: v1
kind: Service
  name:  registry-service-knoweldgejunction
    app: registry
    - name: http
      protocol: TCP
      port: 80
      targetPort: 9376
    - name: https
      protocol: TCP
      port: 443
      targetPort: 9377

Thanks for reading !!! Please feel free to discuss / suggestions / share thoughts !!!


Prasham Sabadra

LIFE IS VERY BEAUTIFUL :) ENJOY THE WHOLE JOURNEY :) Founder of Knowledge Junction and live-beautiful-life.com, Author, Learner, Passionate Techie, avid reader. Certified Professional Workshop Facilitator / Public Speaker. Scrum Foundation Professional certificated. Motivational, Behavioral , Technical speaker. Speaks in various events including SharePoint Saturdays, Boot camps, Collages / Schools, local chapter. Can reach me for Microsoft 365, Azure, DevOps, SharePoint, Teams, Power Platform, JavaScript.

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