Question

Your team runs a global external Application Load Balancer with Cloud CDN enabled in CACHE_ALL_STATIC mode fronting a backend service. During a recent origin outage, clients received many HTTP 404 and 5xx responses. You notice these error responses are being cached at the edge with default TTLs, and stale 404s continued to be served to users even after the objects were restored on the origin. You want to keep error responses out of the cache (or minimize how long they are cached) while retaining normal caching for successful static content. What should you configure?

Accepted Answer

Enable negative caching on the backend service and set a negative caching policy that assigns a TTL of 0 to the specific supported negative-caching status codes (such as 404 and 410) rather than general 5xx status codes.

Answer

Switch the cache mode to USE_ORIGIN_HEADERS so that only responses with explicit Cache-Control headers are cached.

Answer

Issue a cache invalidation with the path /* every time the origin returns an error response.

Answer

Set the default TTL and max TTL on the backend service to 0 to prevent any responses from being cached.