✅ Networking and services in Kubernetes are foundational components that facilitate communication within the cluster and between the cluster and external systems. Here is an in-depth look at these components:

🔗 Networking in Kubernetes

• Flat Network Model: Kubernetes assumes a flat network where every pod can communicate with any other pod without NAT.

• Unique Pod IPs: Each pod gets a unique IP address within the cluster for direct communication.

• Container Network Interface (CNI): CNI plugins manage the networking setup. Popular CNI plugins include:

  • Calico: Offers both networking and network security.

  • Flannel: Simplifies networking by providing layer 3 connectivity.

  • Weave: Supports mesh networking, making it easy to connect containers.

  • Canal: Combines Flannel's networking with Calico's network policy capabilities.

• Service Discovery and DNS

  • CoreDNS: Kubernetes uses CoreDNS for service discovery. It provides DNS-based resolution for services, allowing pods to find and communicate with each other using DNS names rather than IP addresses.

☑️ Services in Kubernetes

↪️ Service Types

1. ClusterIP:

• Description: The default service type, which provides an internal IP for communication within the cluster.

• Usage: Ideal for internal services that do not require external access.

• Example:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376
  type: ClusterIP

2. NodePort:

• Description: Exposes the service on a static port on each node's IP address, allowing external traffic to access the service via <NodeIP>:<NodePort>.

• Usage: Suitable for exposing a service externally on a specific port.

• Example:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  type: NodePort
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376
      nodePort: 30007

3. LoadBalancer:

• Description: Provisions an external load balancer to distribute traffic to the service pods. This service type is typically used in cloud environments.

• Usage: Used to expose services to the internet with automatic load balancing.

• Example:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  type: LoadBalancer
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376

4. ExternalName:

• Description: Maps a service to an external DNS name, allowing pods to access external services using a Kubernetes service.

• Usage: Useful for integrating with external services outside the cluster.

• Example:

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  type: ExternalName
  externalName: my.database.example.com

↪️ Service Components

• Selectors and Labels: Services use selectors to match labels on pods, determining which pods are part of the service.

• Endpoints: Kubernetes automatically creates and updates endpoint objects, which contain the IP addresses and ports of the pods matching the service's selector.

↪️ Ingress

• Ingress Resource: Manages external HTTP and HTTPS access to services, allowing more sophisticated URL-based routing, load balancing, SSL termination, and name-based virtual hosting.

• Ingress Controllers: Implement ingress rules. Examples include NGINX, Traefik, and Istio.

• Example:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: example-ingress
spec:
  rules:
    - host: example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: my-service
                port:
                  number: 80

🔗 Advanced Networking Concepts

↪️ Network Policies

• Network Policies: Define rules for controlling traffic between pods, enhancing security by restricting which pods can communicate with each other.

• Policy Example:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-app
spec:
  podSelector:
    matchLabels:
      app: my-app
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          role: frontend

• Service Mesh: Adds a layer for managing service-to-service communication with advanced traffic management, security, and observability. Examples include Istio, Linkerd, and Consul Connect. Uses sidecar proxies to manage network traffic.

📃 Summary

• Pod-to-Pod Networking: Uses a flat network model with unique IP addresses for each pod, managed by CNI plugins.

• Service Types:

  • ClusterIP for internal services

  • NodePort for exposing services on specific node ports

  • LoadBalancer for cloud-based load balancing

  • ExternalName for integrating external services

• Service Discovery: CoreDNS provides DNS-based service discovery within the cluster.

• Ingress: Manages external access to services with HTTP/HTTPS routing.

• Network Policies: Enhance security by defining rules for traffic flow between pods.

• Service Mesh: Offers advanced traffic management, security, and observability for microservices.