HTTP(S) Load Balancer (Layer 7) in GCP - Step-by-Step Execution

Process Flow - HTTP(S) Load Balancer (Layer 7)

Client sends HTTP(S) request

↓

Load Balancer receives request

↓

Inspect HTTP headers & URL path

↓

Apply routing rules

↓

Backend Service 1

↓

Forward request to selected backend

↓

Backend processes request and sends response

↓

Load Balancer forwards response to client

The HTTP(S) Load Balancer receives client requests, inspects them at Layer 7 (HTTP level), applies routing rules based on headers or URL paths, forwards the request to the right backend, and returns the backend's response to the client.

Execution Sample

GCP

client -> Load Balancer -> Inspect HTTP headers
Load Balancer -> Route to backend based on URL path
Backend -> Process request -> Send response
Load Balancer -> Forward response to client

This flow shows how a client request is handled by the HTTP(S) Load Balancer, routed to the correct backend, and the response is sent back.

Process Table

Step	Action	Input	Decision/Result	Output
1	Client sends HTTP request	GET /images/cat.jpg	Request received by Load Balancer	Request with URL /images/cat.jpg
2	Load Balancer inspects URL path	/images/cat.jpg	Matches path rule /images/*	Route to Backend Service 1
3	Forward request to Backend Service 1	Request with /images/cat.jpg	Backend Service 1 processes request	Response with image data
4	Load Balancer receives backend response	Image data	Prepare response for client	Response ready
5	Load Balancer sends response to client	Response ready	Client receives image	Client displays image
6	Client sends HTTP request	GET /api/data	Request received by Load Balancer	Request with URL /api/data
7	Load Balancer inspects URL path	/api/data	Matches path rule /api/*	Route to Backend Service 2
8	Forward request to Backend Service 2	Request with /api/data	Backend Service 2 processes request	Response with JSON data
9	Load Balancer receives backend response	JSON data	Prepare response for client	Response ready
10	Load Balancer sends response to client	Response ready	Client receives JSON	Client processes data
11	Client sends HTTP request	GET /unknown	Request received by Load Balancer	Request with URL /unknown
12	Load Balancer inspects URL path	/unknown	No matching path rule	Route to default backend
13	Forward request to default backend	Request with /unknown	Default backend processes request	Response with 404 Not Found
14	Load Balancer receives backend response	404 Not Found	Prepare response for client	Response ready
15	Load Balancer sends response to client	Response ready	Client receives 404	Client shows error
16	No more requests	N/A	End of execution	Load Balancer idle

💡 Execution stops when no more client requests are sent.

Status Tracker

Variable	Start	After Step 2	After Step 7	After Step 12	Final
Request URL	N/A	/images/cat.jpg	/api/data	/unknown	N/A
Selected Backend	N/A	Backend Service 1	Backend Service 2	Default Backend	N/A
Response Status	N/A	200 OK	200 OK	404 Not Found	N/A

Key Moments - 3 Insights

Why does the Load Balancer choose Backend Service 1 for the URL /images/cat.jpg?

Because at step 2 in the execution table, the Load Balancer inspects the URL path and finds it matches the path rule /images/*, which routes to Backend Service 1.

What happens if the URL path does not match any routing rule?

As shown at step 12, if no path rule matches, the Load Balancer routes the request to the default backend, which may return a 404 Not Found response.

How does the Load Balancer handle the backend response before sending it to the client?

At steps 4, 9, and 14, the Load Balancer prepares the backend response and then forwards it to the client without modifying the content.

Visual Quiz - 3 Questions

Look at the execution table, which backend service handles the request for /api/data?

A Backend Service 1

B Backend Service 2

C Default Backend

D Load Balancer itself

💡 Hint

Check step 7 and 8 in the execution table where the URL /api/data is routed.

At which step does the Load Balancer decide to route to the default backend?

A Step 2

B Step 7

C Step 12

D Step 15

💡 Hint

Look for the step where the URL path /unknown is inspected and no matching rule is found.

If the client sends a request to /images/dog.jpg, which backend will the Load Balancer route to?

A Backend Service 1

B Backend Service 2

C Default Backend

D No backend, request is dropped

💡 Hint

Refer to the routing rule for /images/* shown in the execution table at step 2.

Concept Snapshot

HTTP(S) Load Balancer (Layer 7):
- Receives client HTTP(S) requests
- Inspects HTTP headers and URL paths
- Routes requests based on rules (e.g., URL path)
- Forwards requests to appropriate backend services
- Returns backend responses to clients
- Supports default backend if no rule matches

Full Transcript

The HTTP(S) Load Balancer works by receiving client requests and inspecting them at the HTTP level. It looks at the URL path or headers to decide which backend service should handle the request. For example, requests to /images/* go to Backend Service 1, while /api/* go to Backend Service 2. If no rule matches, the request goes to a default backend which may return a 404 error. The Load Balancer forwards the backend's response back to the client. This process repeats for each client request, ensuring efficient routing and response delivery.

Practice

1. What is the primary function of an HTTP(S) Load Balancer in Google Cloud Platform?

easy

A. Distribute incoming web traffic across multiple backend services

B. Store user data securely in the cloud

C. Create virtual machines automatically

D. Monitor network latency between regions

Solution

1. Step 1: Understand the role of HTTP(S) Load Balancer

   It is designed to spread incoming web traffic to multiple backend services to improve performance and reliability.

2. Step 2: Eliminate unrelated functions

   Storing data, creating VMs, and monitoring latency are not functions of the load balancer.

3. Final Answer:

   Distribute incoming web traffic across multiple backend services -> Option A

4. Quick Check:

   Load balancer = traffic distribution [OK]

Hint: Load balancer = spreading traffic to backends [OK]

Common Mistakes:

• Confusing load balancer with storage or VM services
• Thinking it monitors network latency
• Assuming it creates resources automatically

2. Which component is NOT part of the HTTP(S) Load Balancer setup in GCP?

easy

A. Cloud Storage bucket

B. Forwarding rule

C. Target proxy

D. URL map

Solution

1. Step 1: Identify components of HTTP(S) Load Balancer

   It includes URL maps, forwarding rules, and target proxies to route traffic.

2. Step 2: Recognize unrelated components

   Cloud Storage bucket is for storing files, not part of load balancing setup.

3. Final Answer:

   Cloud Storage bucket -> Option A

4. Quick Check:

   Storage bucket ≠ load balancer component [OK]

Hint: Storage buckets store files, not route traffic [OK]

Common Mistakes:

• Confusing storage services with load balancer parts
• Mixing forwarding rules with storage buckets
• Assuming all GCP services are load balancer components

3. Given this URL map configuration snippet, which backend service will handle requests to /images/*?

{
  "hostRules": [{"hosts": ["*"], "pathMatcher": "allpaths"}],
  "pathMatchers": [{
    "name": "allpaths",
    "defaultService": "backend-service-default",
    "pathRules": [{"paths": ["/images/*"], "service": "backend-service-images"}]
  }]
}

medium

A. backend-service-default

B. backend-service-images

C. backend-service-static

D. backend-service-api

Solution

1. Step 1: Analyze path rules in URL map

   The path rule for /images/* points to backend-service-images.

2. Step 2: Understand default service role

   Requests not matching specific paths use backend-service-default, but /images/* matches a specific path rule.

3. Final Answer:

   backend-service-images -> Option B

4. Quick Check:

   Specific path rule overrides default service [OK]

Hint: Specific path rules override default backend [OK]

Common Mistakes:

• Choosing default service instead of specific path service
• Ignoring path pattern matching
• Confusing backend service names

4. A user configures an HTTP(S) Load Balancer but finds that requests to /api/* are not routed to the intended backend service. Which is the most likely cause?

medium

A. The backend service is not in the same region

B. The forwarding rule is missing

C. The target proxy is not HTTPS

D. The URL map lacks a path rule for /api/*

Solution

1. Step 1: Check URL map path rules

   If /api/* is missing in path rules, requests won't route correctly.

2. Step 2: Verify other components

   Forwarding rule and target proxy affect traffic flow but missing path rule directly causes routing failure. Backend region mismatch usually causes latency, not routing failure.

3. Final Answer:

   The URL map lacks a path rule for /api/* -> Option D

4. Quick Check:

   Missing path rule = routing failure [OK]

Hint: Check URL map paths if routing fails [OK]

Common Mistakes:

• Assuming forwarding rule absence causes routing error
• Confusing HTTPS proxy with routing logic
• Ignoring URL map path rules

5. You want to design a scalable web application using GCP's HTTP(S) Load Balancer that routes traffic based on URL paths to different backend services. Which design approach ensures high availability and efficient routing?

hard

A. Use a single backend service for all traffic and scale it vertically

B. Deploy multiple forwarding rules each pointing to different backend services without URL maps

C. Configure URL map with path matchers directing to multiple regional backend services behind managed instance groups

D. Use TCP Load Balancer instead of HTTP(S) Load Balancer for path-based routing

Solution

1. Step 1: Understand path-based routing needs

   HTTP(S) Load Balancer uses URL maps with path matchers to route requests to different backends efficiently.

2. Step 2: Ensure scalability and availability

   Using multiple regional backend services behind managed instance groups provides scalability and high availability.

3. Step 3: Evaluate other options

   Single backend limits scalability; multiple forwarding rules without URL maps cannot do path-based routing; TCP Load Balancer does not support Layer 7 routing.

4. Final Answer:

   Configure URL map with path matchers directing to multiple regional backend services behind managed instance groups -> Option C

5. Quick Check:

   URL map + regional backends = scalable routing [OK]

Hint: Use URL maps with regional backends for scalable routing [OK]

Common Mistakes:

• Using single backend limits scalability
• Misusing forwarding rules for path routing
• Choosing TCP Load Balancer for HTTP path routing