Why Host-based routing in Kubernetes? - Purpose & Use Cases

The Big Idea

What if you could run many websites on one server without messy setups or wasted resources?

The Scenario

Imagine you run a website that serves different content for different domains, like shop.example.com and blog.example.com. Without host-based routing, you must manually configure separate servers or IP addresses for each domain.

The Problem

This manual setup is slow and error-prone. You have to manage multiple servers or IPs, update DNS records, and handle traffic routing yourself. It's easy to misroute users or waste resources by running many servers.

The Solution

Host-based routing lets you use one server or load balancer to direct traffic based on the website address users enter. Kubernetes Ingress can automatically send requests to the right service depending on the host name, simplifying management and saving resources.

Before vs After

✗ Before

server {
  listen 80;
  server_name shop.example.com;
  location / {
    proxy_pass http://shop-service;
  }
}

server {
  listen 80;
  server_name blog.example.com;
  location / {
    proxy_pass http://blog-service;
  }
}

✓ After

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

What It Enables

Host-based routing enables you to run multiple websites on a single Kubernetes cluster with simple, centralized traffic control.

Real Life Example

A company hosts its marketing site, customer portal, and blog on the same Kubernetes cluster. Using host-based routing, all traffic is routed correctly without needing separate servers or IPs.

Key Takeaways

Manual routing requires multiple servers and complex setup.

Host-based routing directs traffic by domain name automatically.

Kubernetes Ingress makes managing multiple sites easy and efficient.

Practice

1. What is the main purpose of host-based routing in Kubernetes Ingress?

easy

A. To encrypt all incoming traffic automatically.

B. To balance traffic evenly across all nodes in the cluster.

C. To monitor the health of backend services.

D. To send traffic to different services based on the website address (host).

Solution

1. Step 1: Understand host-based routing concept

   Host-based routing directs requests to services depending on the host name in the URL.

2. Step 2: Compare options to the concept

   Only To send traffic to different services based on the website address (host). matches this behavior; others describe different features.

3. Final Answer:

   To send traffic to different services based on the website address (host). -> Option D

4. Quick Check:

   Host-based routing = directing traffic by host [OK]

Hint: Host-based routing uses website address to choose service [OK]

Common Mistakes:

• Confusing host-based routing with load balancing
• Thinking it encrypts traffic automatically
• Assuming it monitors service health

2. Which of the following is the correct way to specify host-based routing in a Kubernetes Ingress YAML?

easy

A. spec:
host: example.com
paths:
- path: /
serviceName: my-service
servicePort: 80

B. spec:
rules:
- host: example.com
http:
paths:
- path: /
pathType: Prefix
backend:
service:
name: my-service
port:
number: 80

C. metadata:
host: example.com
spec:
service:
name: my-service
port: 80

D. spec:
rules:
- path: example.com
backend:
serviceName: my-service
servicePort: 80

Solution

1. Step 1: Review Kubernetes Ingress host-based routing syntax

   The correct syntax uses 'rules' with 'host' and 'http.paths' specifying backend service details.

2. Step 2: Match options to correct syntax

   spec: rules: - host: example.com http: paths: - path: / pathType: Prefix backend: service: name: my-service port: number: 80 matches the official Kubernetes Ingress spec format for host-based routing.

3. Final Answer:

   spec: rules: - host: example.com http: paths: - path: / pathType: Prefix backend: service: name: my-service port: number: 80 -> Option B

4. Quick Check:

   Correct Ingress host syntax = spec: rules: - host: example.com http: paths: - path: / pathType: Prefix backend: service: name: my-service port: number: 80 [OK]

Hint: Look for 'rules' with 'host' and 'http.paths' in Ingress YAML [OK]

Common Mistakes:

• Placing 'host' under metadata instead of rules
• Using deprecated 'serviceName' and 'servicePort' keys
• Confusing 'path' with 'host' field

3. Given this Ingress rule snippet, what service will receive traffic for host 'app.example.com'?

spec:
  rules:
  - host: app.example.com
    http:
      paths:
      - path: /app
        pathType: Prefix
        backend:
          service:
            name: app-service
            port:
              number: 8080
      - path: /
        pathType: Prefix
        backend:
          service:
            name: default-service
            port:
              number: 80

medium

A. Traffic to app.example.com with path starting /app goes to app-service; others go to default-service.

B. Traffic to app.example.com is rejected because of duplicate host rules.

C. Traffic to app.example.com goes only to default-service on port 80.

D. All traffic to app.example.com goes to app-service on port 8080.

Solution

1. Step 1: Analyze the Ingress rules for host 'app.example.com'

   The rule for host 'app.example.com' has two paths: '/app' and '/'.

2. Step 2: Understand path matching priority

   Requests with path starting '/app' go to 'app-service' on port 8080; all other paths go to 'default-service' on port 80.

3. Final Answer:

   Traffic to app.example.com with path starting /app goes to app-service; others go to default-service. -> Option A

4. Quick Check:

   Host + path routing = Traffic to app.example.com with path starting /app goes to app-service; others go to default-service. [OK]

Hint: Check host and path rules separately to find matching service [OK]

Common Mistakes:

• Assuming all traffic goes to first service listed
• Thinking duplicate hosts cause rejection
• Ignoring path prefixes in routing

4. You created this Ingress YAML but traffic to 'shop.example.com' is not routed correctly. What is the error?

spec:
  rules:
  - host: shop.example.com
    http:
      paths:
      - path: /shop
        backend:
          serviceName: shop-service
          servicePort: 80

medium

A. The keys 'serviceName' and 'servicePort' are deprecated; use 'service.name' and 'service.port.number'.

B. The host field is missing under metadata.

C. The path should be '/' instead of '/shop'.

D. The Ingress resource must have a selector field.

Solution

1. Step 1: Check Ingress backend service syntax

   Modern Kubernetes Ingress requires 'service.name' and 'service.port.number' keys, not 'serviceName' and 'servicePort'.

2. Step 2: Identify the error in YAML

   The YAML uses deprecated keys causing routing failure.

3. Final Answer:

   The keys 'serviceName' and 'servicePort' are deprecated; use 'service.name' and 'service.port.number'. -> Option A

4. Quick Check:

   Use correct backend service keys = The keys 'serviceName' and 'servicePort' are deprecated; use 'service.name' and 'service.port.number'. [OK]

Hint: Use 'service.name' and 'service.port.number' in Ingress backend [OK]

Common Mistakes:

• Using old 'serviceName' and 'servicePort' keys
• Adding host under metadata instead of rules
• Changing path unnecessarily

5. You want to run two websites, 'blog.example.com' and 'shop.example.com', on the same Kubernetes cluster using one Ingress. How should you configure the Ingress rules for host-based routing?

hard

A. Create one rule with host 'example.com' and use paths '/blog' and '/shop' to route to services.

B. Create separate Ingress resources for each host with identical paths.

C. Create two rules under spec.rules, each with a different host and paths pointing to their respective services.

D. Use a single rule with no host specified and rely on path prefixes only.

Solution

1. Step 1: Understand host-based routing for multiple hosts

   To route traffic by host, define separate rules for each host under spec.rules.

2. Step 2: Compare options for best practice

   Create two rules under spec.rules, each with a different host and paths pointing to their respective services. correctly uses two rules with different hosts and paths to route traffic properly.

3. Final Answer:

   Create two rules under spec.rules, each with a different host and paths pointing to their respective services. -> Option C

4. Quick Check:

   Multiple hosts need separate rules = Create two rules under spec.rules, each with a different host and paths pointing to their respective services. [OK]

Hint: Use separate rules for each host in one Ingress resource [OK]

Common Mistakes:

• Using one host with path prefixes instead of separate hosts
• Creating multiple Ingresses unnecessarily
• Not specifying hosts and relying on paths only