Why Ingress resource definition in Kubernetes? - Purpose & Use Cases

The Big Idea

What if you could control all your app traffic with just one simple rule set?

The Scenario

Imagine you have many websites or services running on different servers, and you want to let users access them all through one single address.

Without a smart way to manage this, you would have to tell users exactly which server and port to use for each service.

The Problem

Manually configuring each service's address and port is confusing and error-prone.

Users might get lost or connect to the wrong service.

Also, updating these settings every time you add or change a service takes a lot of time and can cause downtime.

The Solution

An Ingress resource in Kubernetes acts like a smart traffic controller.

It lets you define rules to route user requests to the right service based on the URL or host name.

This way, you only need one entry point, and Kubernetes handles the rest automatically.

Before vs After

✗ Before

kubectl expose pod myapp --port=8080
kubectl expose pod myapi --port=9090
Users must use IP:8080 or IP:9090

✓ After

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

What It Enables

It enables simple, centralized access to multiple services through friendly URLs, improving user experience and operational efficiency.

Real Life Example

A company runs a website, a blog, and an API service on Kubernetes.

Using Ingress, they let users visit www.company.com for the website, blog.company.com for the blog, and api.company.com for the API, all through one IP address.

Key Takeaways

Manual service access is confusing and hard to maintain.

Ingress defines rules to route traffic smartly inside Kubernetes.

This simplifies access and scales easily as services grow.

Practice

1. What is the main purpose of a Kubernetes Ingress resource?

easy

A. To route external HTTP(S) traffic to internal services based on rules

B. To store configuration data for pods

C. To manage persistent storage volumes

D. To schedule pods on specific nodes

Solution

1. Step 1: Understand Ingress role

   An Ingress resource defines rules to route external traffic to services inside the cluster.

2. Step 2: Compare with other resources

   ConfigMaps store config, PersistentVolumes manage storage, and scheduling is done by the scheduler, not Ingress.

3. Final Answer:

   To route external HTTP(S) traffic to internal services based on rules -> Option A

4. Quick Check:

   Ingress routes external traffic [OK]

Hint: Ingress routes external traffic to services inside Kubernetes [OK]

Common Mistakes:

• Confusing Ingress with ConfigMap or PersistentVolume
• Thinking Ingress schedules pods
• Assuming Ingress manages storage

2. Which of the following is the correct minimal YAML snippet to define an Ingress that routes /app path to a service named my-service on port 80?

easy

A. apiVersion: networking.k8s.io/v1\nkind: Service\nmetadata:\n name: example-ingress\nspec:\n selector:\n app: my-service\n ports:\n - protocol: TCP\n port: 80\n targetPort: 80

B. apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: example-ingress\nspec:\n rules:\n - http:\n paths:\n - path: /app\n pathType: Prefix\n backend:\n service:\n name: my-service\n port:\n number: 80

C. apiVersion: v1\nkind: Ingress\nmetadata:\n name: example-ingress\nspec:\n rules:\n - host: example.com\n http:\n paths:\n - path: /app\n backend:\n serviceName: my-service\n servicePort: 80

D. apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: example-ingress\nspec:\n rules:\n - http:\n paths:\n - path: /app\n backend:\n service:\n name: my-service\n port: 8080

Solution

1. Step 1: Check apiVersion and kind

   Correct apiVersion for Ingress is networking.k8s.io/v1 and kind is Ingress.

2. Step 2: Validate backend service and port

   apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: example-ingress\nspec:\n rules:\n - http:\n paths:\n - path: /app\n pathType: Prefix\n backend:\n service:\n name: my-service\n port:\n number: 80 uses correct new syntax with service name and port number 80 matching the question.

3. Final Answer:

   YAML with apiVersion networking.k8s.io/v1, kind Ingress, path /app, service my-service, port 80 -> Option B

4. Quick Check:

   Correct Ingress YAML uses networking.k8s.io/v1 and service port number [OK]

Hint: Use networking.k8s.io/v1 and service.port.number for Ingress backend [OK]

Common Mistakes:

• Using old apiVersion v1 for Ingress
• Using serviceName/servicePort instead of service.name/port.number
• Wrong port number in backend
• Defining Service instead of Ingress

3. Given this Ingress YAML snippet, what host and path will route traffic to web-service?

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

medium

A. Traffic to host example.com and path starting with /web

B. Traffic to any host and path /web

C. Traffic to host example.com and any path

D. Traffic to host example.com and path exactly /web

Solution

1. Step 1: Identify host and path in rules

   The rule specifies host example.com and path /web with pathType Prefix.

2. Step 2: Understand pathType Prefix meaning

   Prefix means any path starting with /web will match, not just exactly /web.

3. Final Answer:

   Traffic to host example.com and path starting with /web -> Option A

4. Quick Check:

   Host and prefix path routing = Traffic to host example.com and path starting with /web [OK]

Hint: Prefix path matches all paths starting with given string [OK]

Common Mistakes:

• Assuming path matches exactly instead of prefix
• Ignoring host field and assuming any host
• Confusing pathType Prefix with Exact

4. You applied this Ingress YAML but traffic is not routing correctly:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: bad-ingress
spec:
  rules:
  - http:
      paths:
      - path: /app
        pathType: Prefix
        backend:
          serviceName: app-service
          servicePort: 80

What is the likely cause of the problem?

medium

A. Missing host field in rules

B. Incorrect apiVersion for Ingress

C. Using deprecated backend syntax serviceName and servicePort instead of service.name and service.port.number

D. Missing metadata name field

Solution

1. Step 1: Check backend syntax in Ingress spec

   The YAML uses old syntax with serviceName and servicePort which is deprecated in networking.k8s.io/v1.

2. Step 2: Confirm correct syntax

   Correct syntax uses service.name and service.port.number fields under backend.service.

3. Final Answer:

   Using deprecated backend syntax serviceName and servicePort instead of service.name and service.port.number -> Option C

4. Quick Check:

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

Hint: Use service.name and service.port.number for backend in networking.k8s.io/v1 [OK]

Common Mistakes:

• Using old backend syntax causing Ingress controller to ignore rules
• Assuming missing host always breaks routing
• Confusing apiVersion correctness
• Forgetting metadata name

5. You want to expose two services, service-a and service-b, on the same IP but different paths /a and /b. Which Ingress YAML snippet correctly defines this?

hard

A. apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: multi-service-ingress\nspec:\n rules:\n - host: example.com\n http:\n paths:\n - path: /a\n pathType: Prefix\n backend:\n service:\n name: service-a\n port:\n number: 80

B. apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: multi-service-ingress\nspec:\n rules:\n - host: example.com\n http:\n paths:\n - path: /a\n backend:\n serviceName: service-a\n servicePort: 80\n - path: /b\n backend:\n serviceName: service-b\n servicePort: 80

C. apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: multi-service-ingress\nspec:\n rules:\n - http:\n paths:\n - path: /a\n pathType: Exact\n backend:\n serviceName: service-a\n servicePort: 80\n - path: /b\n pathType: Exact\n backend:\n serviceName: service-b\n servicePort: 80

D. apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: multi-service-ingress\nspec:\n rules:\n - http:\n paths:\n - path: /a\n pathType: Prefix\n backend:\n service:\n name: service-a\n port:\n number: 80\n - path: /b\n pathType: Prefix\n backend:\n service:\n name: service-b\n port:\n number: 80

Solution

1. Step 1: Check apiVersion and kind

   All options use correct apiVersion and kind for Ingress.

2. Step 2: Validate backend syntax and multiple paths

   apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: multi-service-ingress\nspec:\n rules:\n - http:\n paths:\n - path: /a\n pathType: Prefix\n backend:\n service:\n name: service-a\n port:\n number: 80\n - path: /b\n pathType: Prefix\n backend:\n service:\n name: service-b\n port:\n number: 80 correctly uses service.name and service.port.number with two paths under one rule without host, matching the requirement.

3. Step 3: Compare pathType usage

   Prefix pathType allows routing all requests starting with /a or /b, which is typical for path-based routing.

4. Final Answer:

   Ingress with two paths /a and /b routing to service-a and service-b using correct backend syntax -> Option D

5. Quick Check:

   Multiple paths with service.name and port.number = apiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n name: multi-service-ingress\nspec:\n rules:\n - http:\n paths:\n - path: /a\n pathType: Prefix\n backend:\n service:\n name: service-a\n port:\n number: 80\n - path: /b\n pathType: Prefix\n backend:\n service:\n name: service-b\n port:\n number: 80 [OK]

Hint: Use one rule with multiple paths and service.name/port.number [OK]

Common Mistakes:

• Using deprecated backend syntax serviceName/servicePort
• Missing one of the paths or services
• Using pathType Exact which may limit routing
• Defining only one path instead of two