tool · inferred from evidence
Varnish
A caching HTTP reverse proxy tool producing 503 errors in the described scenario.
- 503 Service Unavailable on Fastly Magento2 admin endpoints (Edge Dictionary ListAll)
After enabling Fastly on a Magento Cloud staging environment, admin pages under Stores > Configuration intermittently showed a red error box ("A technical problem with the server created an error"), with XHR requests like admin/fastlyCdn_Ed