Why URL maps for routing in GCP? - Purpose & Use Cases

The Big Idea

What if your website could automatically send every visitor exactly where they want to go, without you lifting a finger?

The Scenario

Imagine you have a website with many pages and services, and you try to send visitors to the right place by manually checking each web address and forwarding them yourself.

The Problem

This manual way is slow and confusing. You might forget some addresses, send people to wrong pages, or spend hours fixing mistakes. It's like trying to direct traffic without signs or signals.

The Solution

URL maps automatically guide visitors to the right service based on the web address they use. They act like smart traffic signs that know exactly where to send each visitor, making routing easy and reliable.

Before vs After

✗ Before

if url == '/shop': send_to_shop()
elif url == '/blog': send_to_blog()
else: send_to_home()

✓ After

url_map = {
  '/shop': 'shop-service',
  '/blog': 'blog-service',
  '/': 'home-service'
}
route_request(url_map, request)

What It Enables

URL maps let you manage complex website routing simply and scale your services without breaking visitor experience.

Real Life Example

A company uses URL maps to send users to different app parts: shopping, support, or blog, all from one web address, without confusion or delays.

Key Takeaways

Manual routing is slow and error-prone.

URL maps automate and simplify directing visitors.

This improves website reliability and user experience.

Practice

1. What is the main purpose of a URL map in Google Cloud Platform's load balancing?

easy

A. To store user data for web applications

B. To create virtual machines automatically

C. To route incoming web traffic to different backend services based on URL paths or hosts

D. To monitor network traffic usage

Solution

1. Step 1: Understand URL map role

   A URL map directs web traffic to backend services depending on URL patterns.

2. Step 2: Identify correct function

   Routing based on URL paths or hosts matches the description of URL maps.

3. Final Answer:

   To route incoming web traffic to different backend services based on URL paths or hosts -> Option C

4. Quick Check:

   URL maps route traffic = B [OK]

Hint: URL maps decide backend by URL pattern [OK]

Common Mistakes:

• Confusing URL maps with storage or VM services
• Thinking URL maps monitor traffic instead of routing
• Assuming URL maps create resources automatically

2. Which of the following is the correct syntax to define a path matcher in a GCP URL map configuration?

easy

A. "pathMatcher": {"name": "pm1", "defaultService": "backend1"}

B. "pathMatchers": [{"name": "pm1", "defaultService": "backend1"}]

C. "pathMatchers": {"name": "pm1", "defaultService": "backend1"}

D. "pathMatcher": [{"name": "pm1", "defaultService": "backend1"}]

Solution

1. Step 1: Identify correct key for multiple path matchers

   The key for multiple path matchers is plural: "pathMatchers" with an array value.

2. Step 2: Confirm value type

   The value must be an array of objects, so square brackets [] are needed.

3. Final Answer:

   "pathMatchers": [{"name": "pm1", "defaultService": "backend1"}] -> Option B

4. Quick Check:

   Multiple path matchers use "pathMatchers" array = A [OK]

Hint: Use plural "pathMatchers" with array brackets [OK]

Common Mistakes:

• Using singular "pathMatcher" for multiple entries
• Using object instead of array for pathMatchers
• Mixing singular/plural keys incorrectly

3. Given this URL map snippet, which backend service will handle the request to https://example.com/images/logo.png?

{
  "defaultService": "backend-default",
  "pathMatchers": [
    {
      "name": "pm-images",
      "defaultService": "backend-images",
      "pathRules": [
        {"paths": ["/images/*"], "service": "backend-images"}
      ]
    }
  ]
}

medium

A. backend-images

B. No backend matches, request fails

C. backend-logo

D. backend-default

Solution

1. Step 1: Check path rules for "/images/*"

   The path matcher "pm-images" has a path rule matching "/images/*" directing to "backend-images".

2. Step 2: Match request URL path

   The request path "/images/logo.png" matches the "/images/*" pattern, so it routes to "backend-images".

3. Final Answer:

   backend-images -> Option A

4. Quick Check:

   Path "/images/*" matches request = backend-images [OK]

Hint: Match URL path to pathRules first, else defaultService [OK]

Common Mistakes:

• Choosing defaultService without checking pathRules
• Assuming no match causes failure instead of default routing
• Confusing path patterns with exact matches

4. You have this URL map configuration snippet:

{
  "defaultService": "backend-default",
  "pathMatchers": [
    {
      "name": "pm1",
      "defaultService": "backend1",
      "pathRules": [
        {"paths": ["/app/*"], "service": "backend-app"}
      ]
    }
  ]
}

Why does a request to https://example.com/app go to backend-default instead of backend-app?

medium

A. The defaultService overrides all pathRules

B. The path matcher name "pm1" is invalid

C. The backend service "backend-app" is not defined

D. The path "/app" does not match the pattern "/app/*" which requires a trailing slash

Solution

1. Step 1: Understand path pattern matching

   The pattern "/app/*" matches paths starting with "/app/" but not "/app" exactly.

2. Step 2: Check request path against pattern

   The request path "/app" lacks the trailing slash, so it does not match "/app/*" and falls back to defaultService.

3. Final Answer:

   The path "/app" does not match the pattern "/app/*" which requires a trailing slash -> Option D

4. Quick Check:

   Trailing slash matters in path patterns = C [OK]

Hint: Path patterns with * need trailing slash to match [OK]

Common Mistakes:

• Assuming "/app" matches "/app/*" without slash
• Thinking defaultService always overrides pathRules
• Believing backend service must be explicitly defined to route

5. You want to route requests to https://example.com/api/v1/users to backend-v1 and requests to https://example.com/api/v2/users to backend-v2. Which URL map configuration correctly achieves this?

hard

A. {
"defaultService": "backend-default",
"pathMatchers": [
{
"name": "pm-api",
"defaultService": "backend-default",
"pathRules": [
{"paths": ["/api/v1/*"], "service": "backend-v1"},
{"paths": ["/api/v2/*"], "service": "backend-v2"}
]
}
]
}

B. {
"defaultService": "backend-default",
"pathMatchers": [
{
"name": "pm-api",
"defaultService": "backend-v1",
"pathRules": [
{"paths": ["/api/v1/*"], "service": "backend-v1"},
{"paths": ["/api/v2/*"], "service": "backend-v2"}
]
}
]
}

C. {
"defaultService": "backend-default",
"pathMatchers": [
{
"name": "pm-api",
"defaultService": "backend-v2",
"pathRules": [
{"paths": ["/api/v1/*"], "service": "backend-v1"}
]
}
]
}

D. {
"defaultService": "backend-default",
"pathMatchers": [
{
"name": "pm-api",
"defaultService": "backend-default",
"pathRules": [
{"paths": ["/api/*"], "service": "backend-v1"},
{"paths": ["/api/*"], "service": "backend-v2"}
]
}
]
}

Solution

1. Step 1: Check path rules for specific version routing

   { "defaultService": "backend-default", "pathMatchers": [ { "name": "pm-api", "defaultService": "backend-default", "pathRules": [ {"paths": ["/api/v1/*"], "service": "backend-v1"}, {"paths": ["/api/v2/*"], "service": "backend-v2"} ] } ] } defines two distinct path rules: "/api/v1/*" to "backend-v1" and "/api/v2/*" to "backend-v2" which matches requirements.

2. Step 2: Verify defaultService and pathRules consistency

   { "defaultService": "backend-default", "pathMatchers": [ { "name": "pm-api", "defaultService": "backend-default", "pathRules": [ {"paths": ["/api/v1/*"], "service": "backend-v1"}, {"paths": ["/api/v2/*"], "service": "backend-v2"} ] } ] } uses "backend-default" as defaultService, so unmatched paths go there, which is correct.

3. Step 3: Identify issues in other options

   { "defaultService": "backend-default", "pathMatchers": [ { "name": "pm-api", "defaultService": "backend-v1", "pathRules": [ {"paths": ["/api/v1/*"], "service": "backend-v1"}, {"paths": ["/api/v2/*"], "service": "backend-v2"} ] } ] } sets defaultService to "backend-v1" which may misroute unmatched paths. { "defaultService": "backend-default", "pathMatchers": [ { "name": "pm-api", "defaultService": "backend-v2", "pathRules": [ {"paths": ["/api/v1/*"], "service": "backend-v1"} ] } ] } misses "/api/v2/*" pathRule. { "defaultService": "backend-default", "pathMatchers": [ { "name": "pm-api", "defaultService": "backend-default", "pathRules": [ {"paths": ["/api/*"], "service": "backend-v1"}, {"paths": ["/api/*"], "service": "backend-v2"} ] } ] } duplicates "/api/*" paths causing conflict.

4. Final Answer:

   Option A correctly routes /api/v1/* and /api/v2/* to respective backends -> Option A

5. Quick Check:

   Distinct pathRules for versions = A [OK]

Hint: Use distinct pathRules for each version prefix [OK]

Common Mistakes:

• Setting defaultService to one version backend
• Missing pathRule for one version
• Duplicating same path pattern causing conflicts