Caching API responses

For nginx, you'll need to start by configuring a cache zone. The cache zone must be created in the http section, not within server or location.

http {
    ...
    proxy_cache_path /var/cache/nginx keys_zone=gotosocial_ap_public_responses:10m inactive=1w;
}

This configures a cache of 10MB whose entries will be kept up to one week if they're not accessed.

The zone is named gotosocial_ap_public_responses but you can name it whatever you want. 10MB is a lot of cache keys; you can probably use a smaller value on small instances.

Second, we need to update our GoToSocial nginx configuration to actually use the cache for the endpoints we want to cache.

server {
  server_name social.example.org;

  location ~ /.well-known/(webfinger|host-meta)$ {
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-For $remote_addr;
    proxy_set_header X-Forwarded-Proto $scheme;

    proxy_cache gotosocial_ap_public_responses;
    proxy_cache_background_update on;
    proxy_cache_key $scheme://$host$uri$is_args$query_string;
    proxy_cache_valid 200 10m;
    proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504 http_429;
    proxy_cache_lock on;
    add_header X-Cache-Status $upstream_cache_status;

    proxy_pass http://localhost:8080;
  }

  location ~ ^\/users\/(?:[a-z0-9_\.]+)\/main-key$ {
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-For $remote_addr;
    proxy_set_header X-Forwarded-Proto $scheme;

    proxy_cache gotosocial_ap_public_responses;
    proxy_cache_background_update on;
    proxy_cache_key $scheme://$host$uri;
    proxy_cache_valid 200 604800s;
    proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504 http_429;
    proxy_cache_lock on;
    add_header X-Cache-Status $upstream_cache_status;

    proxy_pass http://localhost:8080;
  }

The proxy_pass and proxy_set_header are mostly the same, but the proxy_cache* entries warrant some explanation:

• proxy_cache gotosocial_ap_public_responses tells nginx to use the gotosocial_ap_public_responses cache zone we previously created. If you named it something else, you should change this value
• proxy_cache_background_update on means nginx will try and refresh a cached resource that's about to expire in the background, to ensure it has a current copy on disk
• proxy_cache_key is configured in such a way that it takes the query string into account for caching. So a request for .well-known/webfinger?acct=user1@example.org and .well-known/webfinger?acct=user2@example.org are not seen as the same.
• proxy_cache_valid 200 10m; means we only cache 200 responses from GTS and for 10 minutes. You can add additional lines of these, like proxy_cache_valid 404 1m; to cache 404 responses for 1 minute
• proxy_cache_use_stale tells nginx it's allowed to use a stale cache entry (so older than 10 minutes) in certain cases
• proxy_cache_lock on means that if a resource is not cached and there's multiple concurrent requests for them, the queries will be queued up so that only one request goes through and the rest is then answered from cache
• add_header X-Cache-Status $upstream_cache_status will add an X-Cache-Status header to the response so you can check if things are getting cached. You can remove this.

The provided configuration will serve a stale response in case there's an error proxying to GoToSocial, if our connection to GoToSocial times out, if GoToSocial returns a 5xx status code or if GoToSocial returns 429 (Too Many Requests). The updating value says that we're allowed to serve a stale entry if nginx is currently in the process of refreshing its cache. Because we configured inactive=1w in the proxy_cache_path directive, nginx may serve a response up to one week old if the conditions in proxy_cache_use_stale are met.