GCP Load Balancer Routes /dev/ Prefixed URLs to the Default Backend Instead of Specific Services

Below is one common cause and solution for the behavior you’re seeing.

The Issue

When you set a prefix match value such as

  prefixMatch: /dev/two/

the match is strict for that text. This means that a request for

  /dev/two/anything

will match, but a request for

  /dev/two

(without the trailing slash) does not match. In your case the URLs you are sending (or how the LB normalizes them) may not include the trailing slash, causing none of these rules to fire. When no rule matches the request path, it falls back to the default service.

Removing the “/dev/” portion shifts your match to something like

  prefixMatch: /two/

and it may be matching because it’s more forgiving or because the request URL is actually matching that string.

How to Fix

You need to make sure that your prefixes match the incoming request path exactly. There are two common solutions:

1. Remove the trailing slash from the prefix match.
   For instance, change
     prefixMatch: /dev/two/
     to
     prefixMatch: /dev/two
   This way it matches both /dev/two and /dev/two/anything.

2. Add an additional match rule.
   If you want to enforce having a trailing slash for some reason, add another rule that catches the non-slashed version:

   YAMLCopied
   - matchRules:
       - prefixMatch: /dev/two
     priority: 1
     routeAction:
       weightedBackendServices:
         - backendService: projects/my-project-101010/global/backendServices/two-back-end
           weight: 100
   - matchRules:
       - prefixMatch: /dev/two/
     priority: 2
     routeAction:
       weightedBackendServices:
         - backendService: projects/my-project-101010/global/backendServices/two-back-end
           weight: 100

   That said, usually the first option is simpler.

Other Considerations

• Ordering / Priority:
  Since you already have priorities defined, make sure that lower-numbered (higher priority) rules truly cover the cases you expect.

• Consistency:
  Use the same formatting for all your prefixes. In your YAML some rules include a trailing slash while one (for /dev/five) does not. Inconsistent formatting may lead to unexpected behavior if the requests vary slightly.

Summary

Your default backend is getting hit because the request URL isn’t matching the precise prefix (with trailing slash) specified in your rules. Adjust the prefix match to either omit the trailing slash or add additional rules so that both versions (with and without the slash) are covered. This should ensure that requests matching /dev/two, /dev/three, etc. trigger the intended backend and do not fall back to the default.

Feel free to ask if you need further clarification or help with additional configuration tweaks.