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)
How to fix: 503 Service Unavailable on Fastly Magento2 admin endpoints (Edge Dictionary ListAll). The module's admin XHR calls tripped over Magento Cloud session handling, producing intermittent 503s from Varnish on the Fastly admin endpoin