Embeds are triggering Netlify Function executions

[allanlasser]

We need to optimize our SSR rules between Netlify and Cloudflare to ensure we're correctly caching our pages. Disabling SSR on embeds didn't improve this. It looks like Netlify is sending their default cache-control: no-cache header in responses.

Some approaches @eyeseast and I discussed:

1. Enable prerendering on embed routes
2. Overwriting the cache header with Cloudflare
3. Re-enable SSR with more aggressive caching rules for embeds

Chris experimented by trying #2 and we've seen a reduction in cache misses, so this is likely a headers issue.

Our plan for now:

1. Re-enable SSR on embeds
2. Ensure we're sending correct headers from Netlify
3. Check for correctness on our preview deployment, then merge
4. Check for correctness post-merge through Cloudflare

[eyeseast]

Leaving this open to continue optimization.

[eyeseast]

Test: curl -I 'https://embed.documentcloud.org/documents/25149282-signed-fair-fight-foundation-settlement-2024/?embed=1'

Result:

HTTP/2 200 
date: Wed, 18 Dec 2024 20:06:53 GMT
content-type: text/html
age: 32
cache-control: public,max-age=1200
cache-status: "Netlify Durable"; fwd=miss
cache-status: "Netlify Edge"; fwd=miss
etag: W/"19g4vu1-df"
last-modified: Fri, 18 Oct 2024 14:40:28 GMT
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netlify-vary: query
strict-transport-security: max-age=31536000
vary: Accept-Encoding
x-nf-request-id: 01JFDP1SZ0WYCVNDWEP0AR5KFA
x-sveltekit-page: true
cf-cache-status: HIT
server: cloudflare
cf-ray: 8f41c6ab0d8a8f7b-BOS
alt-svc: h3=":443"; ma=86400

Cloudflare is caching but Netlify isn't. That's better than before. I'm not sure if we can make it better.

[eyeseast]

Another facet of this: SvelteKit uses a __data.json endpoint to preload data, but these have a cache header of private, no-store, so it's creating a bunch of uncached requests.

More here: sveltejs/kit#10348