Cache responses for unauthenticated users

[Nutomic]

This can potentially reduce server load a lot because unauthenticated users trigger much fewer database queries. It will only be effective once lemmy-ui switches from websocket and uses the http api (Lemmy 0.18).

It works fine in a quick test, but will need more testing to make sure it doesnt accidentally leak private data. For now I deployed it on ds9.lemmy.ml

[dessalines]

I wonder what the best way to test this is, to make sure nginx is properly doing caching.

Our isomorphic server, doing local requests, makes this a little complicated to think about.

[miyurusankalpa]

maybe caching static content like images for all users with a larger valid period will also help reduce the load.

Also noticed that the cache control header needs tuning too.

curl -I  https://ds9.lemmy.ml/css/themes/darkly.css
HTTP/2 200 
server: nginx
date: Tue, 06 Jun 2023 17:46:28 GMT
content-type: text/css; charset=utf-8
content-length: 143945
vary: Accept-Encoding
x-powered-by: Express
content-security-policy: default-src 'self'; manifest-src *; connect-src *; img-src * data:; script-src 'self' 'unsafe-inline' 'unsafe-eval'; style-src 'self' 'unsafe-inline'; form-action 'self'; base-uri 'self'; frame-src *
accept-ranges: bytes
cache-control: public, max-age=0
last-modified: Mon, 27 Mar 2023 00:21:59 GMT
etag: W/"23249-18720717458"
strict-transport-security: max-age=63072000
referrer-policy: same-origin
x-content-type-options: nosniff
x-frame-options: DENY
x-xss-protection: 1; mode=block

[Nutomic]

@dessalines This PR sets the header x-cache-status which you can check. See the nginx docs for $upstream_cache_status for details.

[ticoombs]

adding updating can also help here to reduce requests to upstream, when an object expires out of the cache.

[dessalines]

I'd be up for increasing this also.

@Nutomic anything preventing merging this?

[Nutomic]

I deployed it on https://voyager.lemmy.ml/ just now, and it seems to work well. Data is getting cached as expected when user is logged out, and not cached when user is logged in. I also didnt find any leakage of private data.

Though it would be good to update it for using LemmyNet/lemmy-ui#1641 once that is deployed as its a bit cleaner.

[Nutomic]

I had this deployed on lemmy.ml but its not working. The site was logging me out whenever I opened a new tab, and sometimes there were generic error messages which wouldnt go away. We have to wait until there is proper caching support in the projects themselves.

Edit: generic error messages are still happening so those are unrelated to caching, but Im not getting logged out anymore.