Some queries, like on `/your-outfits`, had the cache hint `max-age=0, private` set. In this case, our cache code sent no cache header, on the assumption that no header would result in no caching.
This was true on Vercel, but isn't true on our new Fastly setup! (Which makes sense, Vercel was a bit more aggressive here I think.)
This was causing an arbitrary user's data to be cached by Fastly as the result for `/your-outfits`. (We found this bug before launching the Fastly cache though, don't worry! No actual user data leaked!)
Now, as of this change, the `/your-outfits` query correctly sends a header of `Cache-Control: max-age=0, private`. This directs Fastly not to cache the result.
To fix this, we made a change to our HTTP header code, which is forked from Apollo's stuff.
Oops, we get a _lot_ of outfit image requests, and it's pushing the limits of our free Honeycomb plan! But I don't really need all that much detail, because there's so many.
So, we here apply sampling! `api/outfitImage` is getting a 1/10 rate, and for GraphQL, `ApiOutfitImage` is getting 1/10, and `SearchPanel` is getting 1/5.
I had to add a `addTraceContext` call, to give all the child events awareness of what operation they're being called in, too!
I haven't actually tested that this is working-working, just that the endpoints still return good data. We'll see how it shakes out in prod!
But I did add `console.log(sampleRate, shouldSample, data);` to the `samplerHook` briefly, to see the data flow through, and I reloaded a `SearchPanel` request a few times and observed a plausibly 20% success rate.
Ok cool, so apparently another win we get from using `ts-node` is that I can finally easily use some non-native-Node features like ES module import syntax, for consistency with what I'm doing in the main app source! That was getting on my nerves tbh. Ooh I bet I can finally use `?.` too, I've had to rewrite that a bunch…
Oh yay, I'm pleased with this! I hope it works out well!
stale-while-revalidate is an HTTP caching feature that gives us the ability to still serve relatively static content like item pages ASAP, while also making sure users generally see updates quickly.
The trick is that we declare a period of time where, you can still serve the data from the cache, but you should _then_ go re-fetch the latest data in the background for next time. This works on end users and on the CDN!
I've scanned the basic wardrobe and homepage stuff and brought them up-to-date, and gave particular attention to the item page, which I hope can be very very snappy now! :3
Note to self: Vercel says we can manually clear out a stale-while-revalidate resource by requesting it with `Pragma: no-cache`. I'm not sure it will listen to us for _fresh_ resources, though, so I'm not sure we can actually use that to flush things out in the way I had been hoping until writing this sentence lol :p
This wasn't actually super helpful to read anyway, and I think it was causing us to hit rate limits.
We can maybe add back a limited version to like, add path context of _where_ a span happened in the GQL tree, but like, I feel like that's typically been pretty intuitive so far.
This is in preparation for hiding bio zone restrictions but showing item zone restrictions!
I also refactor the build-cached-data script substantially, to run GraphQL against the server instead of a custom query.
We got bit by the "can't run anything after the response finishes" thing
so I'm just forcing the response to wait for Honeycomb submit to finish
I hope this isn't like, just awful for perf lol. but puts to honeycomb seem fast?
