URL maps for routing in GCP - Step-by-Step Execution

Process Flow - URL maps for routing

Client sends HTTP request

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Load Balancer receives request

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URL Map checks request URL

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Match path rule 1

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Route to backend 1

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Backend serves response

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Response sent to client

The URL map receives the request URL from the load balancer and matches it against defined path rules to route traffic to the correct backend service.

Execution Sample

GCP

urlMap:
  defaultService: backendServiceA
  hostRules:
  - hosts: ["example.com"]
    pathMatcher: pathMatcher1
  pathMatchers:
  - name: pathMatcher1
    defaultService: backendServiceA
    pathRules:
    - paths: ["/images/*"]
      service: backendServiceImages
    - paths: ["/videos/*"]
      service: backendServiceVideos

This URL map routes requests for example.com. Requests to /images/* go to backendServiceImages, /videos/* to backendServiceVideos, and all others to backendServiceA.

Process Table

Step	Request URL	Matched Host	Matched Path Rule	Routed Backend Service	Action
1	http://example.com/images/cat.png	example.com	/images/*	backendServiceImages	Route to images backend
2	http://example.com/videos/movie.mp4	example.com	/videos/*	backendServiceVideos	Route to videos backend
3	http://example.com/about	example.com	default	backendServiceA	Route to default backend
4	http://other.com/home	no match	no match	defaultService (backendServiceA)	Route to default backend because host not matched

💡 Routing completes after matching host and path rules or falls back to default service.

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4
Request URL	none	http://example.com/images/cat.png	http://example.com/videos/movie.mp4	http://example.com/about	http://other.com/home
Matched Host	none	example.com	example.com	example.com	no match
Matched Path Rule	none	/images/*	/videos/*	default	no match
Routed Backend Service	none	backendServiceImages	backendServiceVideos	backendServiceA	backendServiceA

Key Moments - 2 Insights

What happens if the request host does not match any host rule?

If the host does not match any host rule (see step 4 in execution_table), the URL map routes the request to the defaultService backend.

How does the URL map decide which backend to route to when multiple path rules exist?

The URL map checks path rules in order and routes to the backend of the first matching path pattern (see steps 1 and 2). If none match, it uses the defaultService.

Visual Quiz - 3 Questions

Look at the execution_table, which backend service handles the request to 'http://example.com/videos/movie.mp4'?

A backendServiceA

B backendServiceImages

C backendServiceVideos

D No backend matched

💡 Hint

Check row 2 under 'Routed Backend Service' in execution_table.

At which step does the URL map route to the default backend because no path rule matched?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Matched Path Rule' column for 'default' in execution_table.

If the host 'other.com' was added to hostRules with a pathMatcher, how would step 4 change?

A Request would be rejected

B Matched Host would be 'other.com' and routing would follow path rules

C Matched Host remains 'no match' and routes to defaultService

D Routing would fail with error

💡 Hint

Refer to variable_tracker for 'Matched Host' changes and execution_table step 4.

Concept Snapshot

URL maps route incoming requests based on host and path.
Define hostRules to match domains.
Use pathMatchers with pathRules to route paths.
Requests not matching any rule go to defaultService.
This controls traffic flow in GCP load balancing.

Full Transcript

URL maps in GCP load balancing receive client requests and check the URL's host and path. First, the load balancer passes the request to the URL map. The URL map looks for a host rule matching the request's domain. If found, it uses the associated path matcher to check path rules. If a path matches, the request routes to the specified backend service. If no path matches, it routes to the default backend service. If no host matches, the request also routes to the default backend. This process ensures requests go to the right backend based on URL patterns.