CloudNetworking.io
Home / Kubernetes / Ingress
Kubernetes Networking + External Traffic

Kubernetes Ingress explained with real traffic flow

Ingress is one of the most confusing Kubernetes networking topics because it only makes sense when you connect multiple layers together: DNS, load balancer, Ingress controller, Service, and Pods.

This guide explains the full path in simple language so readers understand not only what Ingress is, but also why it exists, how it routes traffic, how TLS fits in, and what actually happens in a real cluster.

Start with the problem Read Services guide Back to Kubernetes Hub

Quick summary

Before going deeper, here is the simplest mental model.

What

Ingress is a set of HTTP or HTTPS routing rules for Services.

Important truth

Ingress does nothing by itself. An Ingress controller must implement it.

Big value

One entry layer can route traffic to multiple Services by host or path.

Easy memory trick: a Service gives stable access to Pods inside the cluster, while Ingress helps external web traffic reach the correct Service.

Why Ingress exists

Before Ingress, a common way to expose an application was to create a separate LoadBalancer Service for each application that needed outside access.

That approach works, but it becomes harder to manage when you have many applications or many routes. You may end up with too many public entry points, repeated TLS setup, and extra cost.

Simple problem example

Imagine you have three web apps:

  • frontend website
  • backend API
  • admin portal

Without a shared entry layer, each one might need its own external exposure method. Ingress lets you centralize that routing instead.

What is Kubernetes Ingress?

Kubernetes Ingress is an API object that describes how external HTTP or HTTPS traffic should be routed to Services inside the cluster.

Ingress understands web-oriented concepts such as:

  • hostnames
  • paths
  • TLS certificates
A Service answers the question “how do I reach this group of Pods?” Ingress answers the question “when web traffic arrives, which Service should receive it?”

Ingress vs Ingress Controller

This is the biggest source of confusion for beginners.

Ingress

The Kubernetes object that contains routing rules.

Ingress Controller

The actual software that watches those rules and configures traffic handling.

Why both matter

Rules without a controller do nothing in practice.

Ingress is like a set of instructions. The controller is the system that reads those instructions and makes real traffic routing happen.

Different controllers may behave differently, which is why documentation often says to check the controller’s own docs for supported features and annotations.

How traffic actually flows

This is the most important part of the whole topic.

User ↓ Public DNS record ↓ External Load Balancer or external entry point ↓ Ingress Controller ↓ Ingress rule match (host/path) ↓ Kubernetes Service ↓ Backend Pod

Step by step

  • A user sends a request to a domain such as app.example.com.
  • DNS resolves that domain to the external entry point for the cluster.
  • Traffic reaches the Ingress controller.
  • The controller checks Ingress rules to see which host or path matches.
  • The request is forwarded to the correct Service.
  • The Service sends traffic to one of the backend Pods.
If readers understand this one flow, Ingress becomes much less confusing.

Routing types: host-based and path-based

Ingress usually routes web traffic in two common ways.

Host-based routing

api.example.com goes to one Service, while admin.example.com goes to another.

Path-based routing

/api goes to one Service, while / goes to a frontend Service.

Combined routing

You can combine host and path rules for more structured application entry.

Real example

A company might use:

  • www.example.com → frontend Service
  • api.example.com → backend API Service
  • www.example.com/admin → admin Service

TLS and HTTPS

One of the biggest reasons teams use Ingress is centralized HTTPS handling. The Ingress layer can terminate TLS, meaning it handles the certificate and decrypts the incoming HTTPS request before forwarding traffic onward.

This gives teams a more centralized place to manage:

  • certificates
  • HTTPS entry
  • multiple web applications behind one entry layer
In practice, the exact TLS behavior depends on the controller and environment, but conceptually Ingress is often where HTTPS entry is managed.

IngressClass and modern configuration

In modern Kubernetes, ingressClassName is used to tell Kubernetes which Ingress controller should handle a given Ingress resource.

This is important in clusters that may have multiple controllers or where the platform team wants clear, explicit behavior.

Ingress idea with class 
spec:
  ingressClassName: nginx
Easy way to think about it: the IngressClass tells Kubernetes which traffic-handling engine should take responsibility for the Ingress rules.

Annotations and controller-specific behavior

Many Ingress controllers support extra features through annotations. These can control things like rewrites, timeouts, redirects, or special routing behavior.

This is one reason Ingress can feel confusing:

  • the main Ingress API is generic
  • controllers implement it differently
  • advanced behavior often depends on controller-specific annotations
That is why two clusters can both “use Ingress” but behave differently in advanced scenarios.

Real-world architecture example

Imagine an online application with three parts:

  • frontend website
  • backend API
  • admin dashboard
Internet ↓ app.cloudnetworking.io ↓ Load Balancer ↓ Ingress Controller ├── / → frontend-service → frontend Pods ├── /api → api-service → backend Pods └── /admin → admin-service → admin Pods

Users see one external entry layer, but traffic is split cleanly to different internal Services.

Why this is powerful

It gives a cleaner architecture, fewer public entry points, easier HTTPS management, and a more maintainable routing model for web applications.

Ingress vs Service

Beginners often confuse these two, so it helps to compare them directly.

Service

Provides stable access to backend Pods.

Ingress

Routes external HTTP or HTTPS traffic to Services.

Relationship

Ingress usually points to Services, not directly to Pods.

Common beginner mistakes

  • thinking Ingress alone handles traffic without a controller
  • confusing Ingress with a Service
  • forgetting that Ingress is mainly for HTTP and HTTPS traffic
  • not understanding where TLS terminates
  • using multiple public LoadBalancers when one shared entry layer would be cleaner
  • ignoring controller-specific behavior and annotations
A very common learning mistake is trying to study Ingress before understanding Pods, Services, and DNS. Ingress becomes much easier once those are already clear.

Common interview questions

  • What is Kubernetes Ingress? An API object that defines HTTP or HTTPS routing to Services.
  • What is an Ingress controller? The software that implements Ingress behavior and handles real traffic.
  • Does Ingress work without a controller? No.
  • What is the difference between Service and Ingress? Service provides stable access to Pods; Ingress routes external web traffic to Services.
  • What is host-based routing? Routing based on domain name.
  • What is path-based routing? Routing based on URL path.
  • What does TLS termination mean? HTTPS is handled at the Ingress layer before traffic continues inward.

Important note for modern Kubernetes readers

Ingress is still widely used and fully valid to learn, but Kubernetes has moved future feature development toward the Gateway API. That means Ingress remains a very important concept, especially for existing clusters and common production setups, while Gateway is the newer direction for richer traffic management.

For your site, it makes sense to teach Ingress first because it is still one of the most recognized Kubernetes traffic entry concepts and many users search for it directly.