They said caching wouldn't work, but they could be wrong. You can't change the Cache-Control header to public for HN responses, because the same URL can appear

They said caching wouldn't work, but they could be wrong. You can't change the Cache-Control header to public for HN responses, because the same URL can appear different to different users. There may be some ways around this, including giving each logged-in user their own URL to browse with. But that might be a lot of work. You can still set up a proxy that kicks in only for requests that don't contain a session cookie. Then, requests without a cookie can be responded to with a cached copy from Varnish, and Varnish could refresh every 30 seconds or so. That might reduce the number of connections to MzScheme by quite a lot.