In this case GN3 (which runs on port 8087) has a web endpoint of /api4 (this is arbitrarily named for testing, will probably change later).
For example, https://genenetwork.org/api4/... will send requests to GN3
A recent issue involves a web form being submitted to GN3, which then redirects back to another page. As a result, '/api4/' always needs to be prepended to the various URIs. By using the nginx configurations, this doesn't need to be passed as a setting to the actual GN3 code (I think this is why it's done this way).
This was dealt with using the following configurations (full configurations are pasted below): - The sub_filter setting replaces instances of '/api/' in the HTML with '/api4/api/', which addresses the log-in form passing the next_uri (which is passed into flask's redirect() function) to GN3 - The proxy_redirect setting handles the flask redirect. The flask redirect is to /api/oauth2/admin/dashboard, which ends up as https://genenetwork.org/api/oauth2/admin/dashboard. The proxy_redirect setting then redirects this to https://genenetwork.org/api4/api/oauth2/admin/dashboard
location /api4 {
rewrite /api4/(.*) /$1 break;
rewrite /api/(.*) /api4/api/$1 redirect;
proxy_pass http://127.0.0.1:8087;
proxy_redirect /api/ /api4/api/;
sub_filter '/api/' '/api4/api/';
sub_filter_once off;
proxy_set_header Host $host;
}