How to verify if a Cloud CDN response was a cache hit (or comes from CDN)

Question

I have a backend GCS bucket behind a Google Cloud HTTP(S) load balancer with Cloud CDN enabled.

I'm trying to answer these questions based on response headers:

• was this response served from CDN
• if so which location/region
• was this a cache hit/miss

Here are the response headers. Based on cache-control, in theory, this should be cached. However, I don't see an indication of this that can verify CDN works correctly. Similarly all other headers x-goog-* and Server: UploadServer are seem to be coming from GCS server, not CDN.

accept-ranges: bytes
age: 551
alt-svc: clear
cache-control: public, max-age=3600
content-length: 298303
content-type: image/jpeg
date: Wed, 05 Aug 2020 23:07:33 GMT
etag: "f0b6c60f635c784dd7f34ab9c1527867"
expires: Thu, 06 Aug 2020 00:07:33 GMT
last-modified: Wed, 05 Aug 2020 23:07:16 GMT
server: UploadServer
status: 200
X-DNS-Prefetch-Control: off
x-goog-generation: 1596668836233926
x-goog-hash: crc32c=rD4sZw==
x-goog-hash: md5=8LbGD2NceE3X80q5wVJ4Zw==
x-goog-metageneration: 1
x-goog-storage-class: STANDARD
x-goog-stored-content-encoding: identity
x-goog-stored-content-length: 298303
x-guploader-uploadid: AAANsUktJ98kPCHjiR2oBi6N-[...]

For example, Cloudflare provides these response headers:

• where was the request served: cf-ray: 5be4505beb76bca2-SEA
• what was the cache status: cf-cache-status: REVALIDATED
• was my request hitting CDN or my backend directly server: cloudflare

Answer 1

There is now a new {cdn_cache_status} variable that you can set in the response: https://cloud.google.com/load-balancing/docs/custom-headers#variables

Using gcloud SDK v309.0.0 or greater:

➜  gcloud beta compute backend-services update my-backend --global \
--enable-cdn \
--custom-response-header='Cache-Status: {cdn_cache_status}' \
--custom-response-header='Cache-ID: {cdn_cache_id}'

Example output:

< HTTP/2 200
< content-type: text/plain; charset=utf-8
< date: Mon, 14 Sep 2020 21:40:05 GMT
< server: Google Frontend
< content-length: 1098
< via: 1.1 google
< cache-control: public, max-age=10
< age: 2
< x-frame-options: DENY
< cache-status: hit