GKE Ingress with Load Balancer in GCP - Time & Space Complexity

Time Complexity: GKE Ingress with Load Balancer

O(n)

Understanding Time Complexity

When using GKE Ingress with a Load Balancer, it's important to understand how the system handles incoming traffic as it grows.

We want to know how the processing time changes when more requests or services are added.

Scenario Under Consideration

Analyze the time complexity of the following GKE Ingress setup commands.

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

This snippet defines an Ingress resource routing traffic to a service through a Load Balancer.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The Load Balancer processes each incoming request and routes it to the correct backend service.
• How many times: Once per incoming request, which can be many and grow with traffic.

How Execution Grows With Input

As the number of incoming requests increases, the Load Balancer handles each one individually.

Input Size (n requests)	Approx. Operations
10	10 routing operations
100	100 routing operations
1000	1000 routing operations

Pattern observation: The number of operations grows directly with the number of requests.

Final Time Complexity

Time Complexity: O(n)

This means the processing time grows linearly with the number of incoming requests.

Common Mistake

[X] Wrong: "Adding more backend services will slow down each request significantly."

[OK] Correct: The Load Balancer routes requests based on rules, so adding services does not increase time per request, only the total number of requests affects processing time.

Interview Connect

Understanding how GKE Ingress and Load Balancers scale with traffic helps you design systems that handle growth smoothly and predict performance.

Self-Check

"What if we added caching at the Load Balancer level? How would the time complexity change?"

Practice

1. What is the main purpose of using an Ingress with a Load Balancer in GKE?

easy

A. To restrict access to the cluster nodes only

B. To expose multiple services through a single external IP address

C. To create multiple IP addresses for each pod

D. To manage internal DNS records automatically

Solution

1. Step 1: Understand Ingress role in GKE

   Ingress allows routing external traffic to multiple services inside the cluster using one IP.

2. Step 2: Recognize Load Balancer function

   The Load Balancer created by Ingress exposes a single external IP to route traffic.

3. Final Answer:

   To expose multiple services through a single external IP address -> Option B

4. Quick Check:

   Ingress + Load Balancer = Single IP for many services [OK]

Hint: Ingress combines services under one IP address [OK]

Common Mistakes:

• Thinking each pod gets its own IP
• Confusing internal DNS with external exposure
• Assuming Load Balancer creates multiple IPs

2. Which annotation is used in a GKE Ingress resource to specify the creation of a Google Cloud HTTP(S) Load Balancer?

easy

A. cloud.google.com/load-balancer-type: 'internal'

B. kubernetes.io/ingress.class: 'nginx'

C. kubernetes.io/ingress.class: 'gce'

D. networking.gke.io/load-balancer: 'external'

Solution

1. Step 1: Identify GKE Ingress annotation for Load Balancer

   The annotation 'kubernetes.io/ingress.class: gce' tells GKE to use Google Cloud Load Balancer.

2. Step 2: Differentiate from other ingress classes

   'nginx' is for NGINX ingress controller, not GCP Load Balancer.

3. Final Answer:

   kubernetes.io/ingress.class: 'gce' -> Option C

4. Quick Check:

   Use 'gce' annotation for GCP Load Balancer [OK]

Hint: Use 'kubernetes.io/ingress.class: gce' for GCP Load Balancer [OK]

Common Mistakes:

• Using 'nginx' instead of 'gce' annotation
• Confusing internal vs external load balancer annotations
• Using non-existent annotation keys

3. Given this Ingress YAML snippet, what will happen when a user visits http://example.com/api?

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

medium

A. Traffic to /api goes to api-service; all other paths go to web-service

B. Traffic to /api goes to web-service; all other paths go to api-service

C. All traffic goes to api-service regardless of path

D. Ingress will reject traffic because of conflicting paths

Solution

1. Step 1: Analyze path rules in Ingress

   The rule for path '/api' with pathType Prefix directs matching requests to 'api-service'.

2. Step 2: Understand default path routing

   The path '/' with Prefix matches all other requests and routes them to 'web-service'.

3. Final Answer:

   Traffic to /api goes to api-service; all other paths go to web-service -> Option A

4. Quick Check:

   Specific path matches first, then default [OK]

Hint: Specific paths route before general '/' path [OK]

Common Mistakes:

• Assuming '/' path overrides /api
• Thinking all traffic goes to one service
• Believing Ingress rejects overlapping paths

4. You created an Ingress with annotation kubernetes.io/ingress.class: nginx in GKE but no external IP is assigned. What is the likely cause?

medium

A. GKE does not create a Google Cloud Load Balancer for 'nginx' ingress class

B. The Ingress resource is missing the service port definition

C. The cluster nodes are not labeled correctly

D. The Ingress controller is automatically created and running

Solution

1. Step 1: Understand Ingress class annotation effect

   Annotation 'nginx' tells GKE to use NGINX ingress controller, which does not create a GCP Load Balancer automatically.

2. Step 2: Recognize Load Balancer creation requirements

   Only 'gce' ingress class triggers Google Cloud Load Balancer creation with external IP.

3. Final Answer:

   GKE does not create a Google Cloud Load Balancer for 'nginx' ingress class -> Option A

4. Quick Check:

   'nginx' ingress needs separate controller, no auto Load Balancer [OK]

Hint: Use 'gce' annotation for auto Load Balancer in GKE [OK]

Common Mistakes:

• Assuming 'nginx' creates GCP Load Balancer automatically
• Blaming missing service port for no IP
• Thinking cluster node labels affect Load Balancer creation

5. You want to expose two services, frontend and backend, on the same IP but different paths using GKE Ingress with a Load Balancer. Which YAML snippet correctly configures this?

hard

A. apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: multi-service-ingress
annotations:
kubernetes.io/ingress.class: "gce"
spec:
rules:
- http:
paths:
- path: /frontend
pathType: Prefix
backend:
service:
name: frontend
port:
number: 80
- path: /backend
pathType: Prefix
backend:
service:
name: backend
port:
number: 80

B. apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: multi-service-ingress
spec:
rules:
- host: "*"
http:
paths:
- path: /frontend
backend:
serviceName: frontend
servicePort: 80
- path: /backend
backend:
serviceName: backend
servicePort: 80

C. apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: multi-service-ingress
annotations:
kubernetes.io/ingress.class: "nginx"
spec:
rules:
- host: example.com
http:
paths:
- path: /frontend
pathType: Prefix
backend:
service:
name: frontend
port:
number: 80
- path: /backend
pathType: Prefix
backend:
service:
name: backend
port:
number: 80

D. apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: multi-service-ingress
annotations:
kubernetes.io/ingress.class: "gce"
spec:
rules:
- host: example.com
http:
paths:
- path: /frontend
pathType: Prefix
backend:
service:
name: frontend
port:
number: 80
- path: /backend
pathType: Prefix
backend:
service:
name: backend
port:
number: 80

Solution

1. Step 1: Confirm correct annotation for GCP Load Balancer

   Options A and D use 'kubernetes.io/ingress.class: gce', which is correct for GKE Load Balancer.

2. Step 2: Check pathType and host usage

   apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: multi-service-ingress annotations: kubernetes.io/ingress.class: "gce" spec: rules: - host: example.com http: paths: - path: /frontend pathType: Prefix backend: service: name: frontend port: number: 80 - path: /backend pathType: Prefix backend: service: name: backend port: number: 80 uses 'Prefix' pathType with a host, ensuring precise routing for /frontend and /backend paths on example.com.

3. Step 3: Identify deprecated or incorrect syntax

   apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: multi-service-ingress spec: rules: - host: "*" http: paths: - path: /frontend backend: serviceName: frontend servicePort: 80 - path: /backend backend: serviceName: backend servicePort: 80 uses deprecated 'serviceName' and 'servicePort' keys and lacks annotation; apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: multi-service-ingress annotations: kubernetes.io/ingress.class: "nginx" spec: rules: - host: example.com http: paths: - path: /frontend pathType: Prefix backend: service: name: frontend port: number: 80 - path: /backend pathType: Prefix backend: service: name: backend port: number: 80 uses 'nginx' ingress class, not GCE; apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: multi-service-ingress annotations: kubernetes.io/ingress.class: "gce" spec: rules: - http: paths: - path: /frontend pathType: Prefix backend: service: name: frontend port: number: 80 - path: /backend pathType: Prefix backend: service: name: backend port: number: 80 is missing host and incomplete.

4. Final Answer:

   Option D correctly configures two services on same IP with prefix path matching and GCE Load Balancer -> Option D

5. Quick Check:

   Use 'gce' annotation + prefix paths + host for precise multi-service routing [OK]

Hint: Use 'gce' annotation and prefix pathType for multi-service routing [OK]

Common Mistakes:

• Using 'nginx' annotation instead of 'gce'
• Using deprecated serviceName/servicePort keys
• Not specifying host or using wrong pathType