What is a Kubernetes Ingress Controller? A Guide to Smart Traffic Routing

So, you've deployed your first application on Kubernetes and exposed it with a LoadBalancer Service. It works perfectly! You get a public IP address, and users can reach your app. But then you deploy a second microservice. And a third. Do you create a new LoadBalancer for each one?

You could, but your cloud bill would quickly start to climb. Each LoadBalancer Service you create provisions a new, dedicated load balancer from your cloud provider, and each one has a cost. Managing a dozen different public IP addresses is also an operational nightmare. There has to be a smarter way to manage traffic, right?

Absolutely. This is the exact problem that Kubernetes Ingress and the Ingress Controller are designed to solve. They act as a single, intelligent front door for all the services running in your cluster.

In this guide, we'll explain what an Ingress resource is, why it's useless without an Ingress Controller, and how they work together to provide powerful, efficient, and cost-effective traffic routing for your applications.

The Problem: The High Cost of LoadBalancer Services

A Service of type LoadBalancer is a fantastic tool for exposing a single application. It's simple and direct. However, as your architecture grows to include multiple microservices (like an API, a frontend, a billing service, etc.), this one-to-one model becomes a major bottleneck.

• It's Expensive: Every LoadBalancer Service maps to a real cloud load balancer (like an AWS ELB or a Google Cloud Load Balancer), which costs money. Exposing 10 services means paying for 10 separate load balancers.
• It's Inefficient: Managing a long list of unique IP addresses for your services is complex. DNS configuration becomes a chore, and you lose a centralized point of control.

Analogy time: Imagine your office building decided to give every single department its own front door to the main street. It would be architecturally absurd, incredibly expensive to build and maintain, and a security nightmare. A much better approach is a single main entrance with a reception desk that directs visitors to the right place.

The Ingress Controller is that main entrance and reception desk for your Kubernetes cluster.

Step 1: Kubernetes Ingress — The Rulebook

First, it's crucial to understand that a Kubernetes Ingress is just a configuration object. It's a set of rules, written in YAML, that defines how external HTTP and HTTPS traffic should be routed to internal services.

By itself, an Ingress object does nothing. It doesn't have any code or logic. It's purely declarative.

Think of an Ingress as the building directory in the lobby. It contains a list of rules like:

• If a request comes in for shop.example.com, send it to the shopping-cart-service.
• If a request comes in for example.com/api, send it to the user-api-service.
• Any other traffic for example.com should go to the frontend-web-service.

This rulebook is incredibly useful, but it needs someone to actually read it and enforce the rules.

Here's a sample Ingress resource:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: simple-fanout-ingress
spec:
  rules:
    - host: myapp.example.com
      http:
        paths:
          - path: /login
            pathType: Prefix
            backend:
              service:
                name: login-service # <-- Rule 1
                port:
                  number: 8080
          - path: /api
            pathType: Prefix
            backend:
              service:
                name: api-service # <-- Rule 2
                port:
                  number: 8080

Step 2: The Ingress Controller — The Brains of the Operation

The Ingress rules are useless without the engine that enforces them: the Ingress Controller.

An Ingress Controller is the missing piece of the puzzle. It's an actual application—typically a powerful reverse proxy like NGINX, Traefik, or HAProxy—that runs in a Pod inside your cluster. Its job is to:

1. Watch the Kubernetes API for any Ingress resources.
2. Read the routing rules defined in those resources.
3. Dynamically configure itself to implement those rules.

So, the workflow is:

1. You create a single LoadBalancer Service that points to your Ingress Controller Pod. This is the only cloud load balancer you'll need.
2. All external traffic enters your cluster through this single entry point.
3. The Ingress Controller inspects the incoming request (e.g., the hostname or URL path).
4. It consults its "rulebook" (the Ingress resources) and forwards the traffic to the correct internal Service.

To continue our analogy, the Ingress Controller is the receptionist or security guard in the lobby. They look at the building directory (the Ingress rules) and then physically direct the visitor (the traffic) to the correct department (the internal Service).

This model is vastly more efficient. You only pay for one cloud load balancer and gain a single, centralized point for managing traffic, security policies, and TLS certificates.

Common Ingress Features and Strategies

Ingress Controllers unlock powerful routing capabilities beyond what a simple LoadBalancer can do.

• Host-Based Routing: Route traffic based on the domain name. api.example.com goes to the API service, while www.example.com goes to the web frontend.
• Path-Based Routing: Route traffic based on the URL path. example.com/blog goes to your blogging service, while example.com/shop goes to your e-commerce service.
• TLS/SSL Termination: The Ingress Controller can handle TLS certificates for your domains. It terminates the encrypted HTTPS connection and forwards unencrypted traffic to your internal services. This centralizes certificate management and offloads the computational work of encryption from your applications.

Effortless Ingress Management with Sealos

While an Ingress Controller is incredibly powerful, deploying, configuring, and managing one (like the popular NGINX Ingress Controller) still requires significant operational effort. You have to install it with Helm or YAML, configure its permissions, and manage its lifecycle.

Sealos makes this effortless. The Sealos platform comes with a robust, pre-configured Ingress Controller built right in. You don't have to install or manage anything.

When you deploy an application through the Sealos UI, exposing it to the public is as simple as filling out a form. You can specify a custom domain, and Sealos will automatically:

• Create the necessary Ingress resource for you.
• Configure the routing rules.
• Provision and manage a TLS certificate for HTTPS.

What takes hours of manual setup in a standard Kubernetes environment becomes a simple, 30-second task on Sealos, giving you a secure, public URL for your application instantly.

Conclusion

The Kubernetes Ingress Controller is the smart and scalable solution for managing external access to your applications. It solves the cost and complexity problems of using a LoadBalancer for every service. By pairing a declarative Ingress resource (the rulebook) with an active Ingress Controller (the engine), you create a single, intelligent entry point for all your cluster's traffic.

This architecture is not just more efficient—it's the standard for running production workloads on Kubernetes.

Ready to master advanced traffic routing without the YAML gymnastics? Deploy your application on Sealos and get a public domain in just a few clicks.