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

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Load Balancer receives request

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Inspect HTTP headers & URL path

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Apply routing rules

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Backend Service 1

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Forward request to selected backend

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Backend processes request and sends response

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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.