Kubernetes Ingress Controllers Explained

Kubernetes Ingress Controllers are components that manage external access to services running in a Kubernetes cluster, typically via HTTP/HTTPS. They act as a reverse proxy and load balancer, routing incoming traffic to the appropriate backend services based on rules defined in Ingress resources.

Key Concepts:

1. Ingress Resource:

   • A Kubernetes object that defines rules for routing external HTTP/HTTPS traffic to services within the cluster.
   • Specifies hostnames, paths, and backend services.

2. Ingress Controller:

   • The actual implementation that enforces the rules defined in the Ingress resource.
   • Listens for changes to Ingress resources and configures the underlying load balancer or proxy (e.g., NGINX, Envoy, HAProxy) to route traffic accordingly.

3. How It Works:

   • The Ingress Controller monitors the Kubernetes API for Ingress resources.
   • When an Ingress resource is created or updated, the controller configures the proxy/load balancer to route traffic based on the defined rules.
   • External traffic is directed to the appropriate service and pod based on the hostname, path, or other criteria.

Key Features:

• Traffic Routing: Routes traffic to different services based on hostnames or URL paths.
• SSL/TLS Termination: Handles HTTPS traffic by terminating SSL/TLS at the Ingress level.
• Load Balancing: Distributes traffic across multiple backend pods.
• Authentication and Authorization: Can integrate with identity providers for secure access.
• Rate Limiting and Caching: Some controllers offer advanced features like rate limiting and caching.

Popular Ingress Controllers:

• NGINX Ingress Controller: Uses NGINX as the underlying proxy.
• Traefik: A modern, dynamic reverse proxy with built-in support for Kubernetes.
• HAProxy Ingress: Known for high performance and reliability.
• Istio Ingress Gateway: Part of the Istio service mesh, offering advanced traffic management.
• AWS ALB Ingress Controller: Integrates with AWS Application Load Balancer for EKS clusters.

Use Cases:

• Exposing web applications to the internet.
• Managing multiple domains or subdomains in a single cluster.
• Implementing canary deployments or A/B testing.
• Securing applications with SSL/TLS and authentication.

In summary, Kubernetes Ingress Controllers are essential for managing external access to services in a Kubernetes cluster, providing routing, load balancing, and security features.