kubernetes-training

Pod

• IP address is assigned to pod
• IP address is changed when pod is recreated

  Cluster Networking

• Kubernetes doesn’t automatically set up so that pods are assigned different IP addresses
• Fundamental rules:
  1. All the containers or PODs in a kubernetes cluster MUST be able to communicate with one another without having to configure NAT. –> solutions available in the industry.

Services

Kubernetes Services enable communication between various components within and outside of the application. Kubernetes Services helps us connect applications together with other applications or users.

Nodeport service

• Listen to a port on the Node and forward requests on that port to a port on the POD running the web application.
• NodePort is the service makes an internal POD accessible on a Port on the Node.
• Port on pod: target pod
• Port on service. The service is in fact like a virtual server inside the node. Inside the cluster it has its own IP address. And that IP address is called the Cluster-IP of the service

• Port on the Node itself which we use to access the web server externally. NodePorts can only be in a valid range which is from 30000 to 32767

• Cluster IP: the service creates a virtual IP inside the cluster to enable communication between different services.

• There could be multiple port mappings within a single service.

To link the service to the pod, bring the labels section of pod-definition.yaml to selector

![[Pasted_image_20240626085826.png]]

• In the production’s env, service file with match selector with labels of pod, service will then distribute the balance automatically. It also map the pod to the nodeport, making it available to users.

Cluster IP

![[Pasted image 20240626094726.png]]

• The targetPort is the port where the backend is exposed
• The port is where the service is exposed

Load balancer

Differences between Nodeport, ClusterIP, and Loadbalancer