Host-based routing in Kubernetes - Step-by-Step Execution

Process Flow - Host-based routing

Client sends HTTP request

↓

Ingress Controller receives request

↓

Check Host header in request

↓

Host matches site1

↓

Route to service1

↓

Service handles request

The ingress controller receives a request and routes it to different services based on the Host header in the HTTP request.

Execution Sample

Kubernetes

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: example-ingress
spec:
  rules:
  - host: site1.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: service1
            port:
              number: 80
  - host: site2.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: service2
            port:
              number: 80

This ingress routes requests to service1 or service2 depending on the Host header.

Process Table

Step	Request Host	Ingress Rule Matched	Service Routed To	Action
1	site1.example.com	host: site1.example.com	service1	Request routed to service1
2	site2.example.com	host: site2.example.com	service2	Request routed to service2
3	unknown.example.com	no matching host	none	Request rejected or default backend used

💡 Routing stops after matching host or no match found

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
Request Host	none	site1.example.com	site2.example.com	unknown.example.com
Matched Rule	none	host: site1.example.com	host: site2.example.com	none
Routed Service	none	service1	service2	none

Key Moments - 2 Insights

Why does a request with an unknown host not get routed to any service?

Because the ingress rules only match specific hosts (see execution_table row 3). If no host matches, the request is rejected or sent to a default backend if configured.

Can multiple hosts route to the same service?

Yes, you can define multiple host rules pointing to the same service. Each host is checked independently as shown in the concept flow.

Visual Quiz - 3 Questions

Look at the execution table, which service handles the request when the host is site2.example.com?

A service2

B none

C service1

D default backend

💡 Hint

Check execution_table row 2 under 'Routed Service'

At which step does the ingress controller find no matching host rule?

A Step 1

B Step 3

C Step 2

D None

💡 Hint

See execution_table row 3 'Ingress Rule Matched' column

If a new host rule for site3.example.com routing to service3 is added, what changes in the variable tracker?

A Matched Rule will always be none

B A new row for service3 is added

C Request Host variable will include site3.example.com after a new request

D Routed Service will be empty

💡 Hint

Variable tracker shows Request Host changes per step; adding a new host means new requests can have that host

Concept Snapshot

Host-based routing in Kubernetes Ingress:
- Routes HTTP requests based on the Host header
- Define multiple host rules in ingress spec
- Each host routes to a specific backend service
- Requests with unmatched hosts are rejected or use default backend
- Enables hosting multiple sites on one ingress controller

Full Transcript

Host-based routing in Kubernetes means the ingress controller looks at the Host header in incoming HTTP requests. It compares this host to the rules defined in the ingress resource. If the host matches a rule, the request is sent to the backend service specified for that host. If no host matches, the request is rejected or sent to a default backend if configured. This allows one ingress controller to serve multiple websites or services by routing requests based on their hostnames.