429 errors on image URLS generated by the App Engine Images API (getServingUrl)

Google Cloud Serverless Applications
1

Hi all,

Starting 17-03-2026, We’re seeing intermittent HTTP 429 (Too Many Requests) errors when loading images via App Engine Images API (getServingUrl).

Setup

  • Serving URLs are generated via getServingUrl

  • These URLs are stored and reused (not generated on each request)

  • Pages can contain multiple images that load at once using these stored URLs

  • This setup has been stable for years with no recent changes

Issue

  • Images fail to load when multiple are requested on a page

  • Opening the same image URL individually works fine

  • Issue resolves itself after ~10–60 minutes

  • No quota limits are hit (nothing visible in GCP quotas)

  • No clear related errors in our logs found

Question
Where could these 429s be coming from if nothing shows up in quotas?

Specifically:

  • Are there hidden/legacy limits behind the serving infrastructure?

  • Any tips on where to debug this (logs, headers, metrics)?

Any pointers on what to check would really help.

Thanks in advance!

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