URL maps for routing in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a URL map in Google Cloud Platform?

A URL map is a configuration that directs incoming web traffic to different backend services based on the URL path or host. It helps route users to the right place.

beginner

How does a URL map decide where to send a request?

It checks the URL's host and path against rules you set. When it finds a match, it sends the request to the backend service linked to that rule.

intermediate

What is a host rule in a URL map?

A host rule matches the domain name part of a URL (like example.com) and connects it to path matchers that further decide routing based on URL paths.

intermediate

Why use path matchers in URL maps?

Path matchers let you send different URL paths (like /images or /videos) to different backend services, helping organize traffic efficiently.

beginner

What happens if no URL map rule matches a request?

The request is sent to the default backend service defined in the URL map, ensuring traffic is always handled even if no specific rule matches.

What does a URL map primarily control in GCP?

A Storage of website files

B Routing of incoming web requests to backend services

C User authentication

D Database connections

URL maps control how incoming web requests are routed to backend services based on URL patterns.

Which part of the URL does a host rule in a URL map match?

A The domain name (host)

B The URL path

C The query parameters

D The HTTP headers

Host rules match the domain name part of the URL to decide routing.

If a URL path is '/images', where does the URL map send the request?

A To the database

B To the default backend service only

C To the firewall

D To the backend service linked to the '/images' path matcher

Path matchers route requests based on URL paths like '/images' to specific backend services.

What happens if no host or path rule matches a request in a URL map?

A The request goes to the default backend service

B The request is dropped

C The request is sent to a random backend

D The request is redirected to the homepage

Requests with no matching rules are sent to the default backend service to ensure handling.

Which GCP service commonly uses URL maps for routing?

A Cloud Functions

B Cloud Storage

C Cloud Load Balancing

D BigQuery

Cloud Load Balancing uses URL maps to route traffic to backend services.

Explain how URL maps route traffic in Google Cloud Platform.

Think about how a traffic director sends cars to different roads based on signs.

Describe the role of host rules and path matchers in URL maps.

Host rules are like street names, path matchers are like house numbers.

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