nginx.conf

worker_processes 1;
events {
    worker_connections 1024;
}
http {
    upstream lemmy {
        # this needs to map to the lemmy (server) docker service hostname
        server "lemmy:8536";
    }
    upstream lemmy-ui {
        # this needs to map to the lemmy-ui docker service hostname
        server "lemmy-ui:1234";
    }

    server {
        # this is the port inside docker, not the public one yet
        listen 80;
        # change if needed, this is facing the public web
        server_name localhost;
        server_tokens off;

        gzip on;
        gzip_types text/css application/javascript image/svg+xml;
        gzip_vary on;

        # Upload limit, relevant for pictrs
        client_max_body_size 20M;

        add_header X-Frame-Options SAMEORIGIN;
        add_header X-Content-Type-Options nosniff;
        add_header X-XSS-Protection "1; mode=block";

        # frontend general requests
        location / {
            # distinguish between ui requests and backend
            # don't change lemmy-ui or lemmy here, they refer to the upstream definitions on top
            set $proxpass "http://lemmy-ui";

            if ($http_accept ~ "^application/.*$") {
              set $proxpass "http://lemmy";
            }
            if ($request_method = POST) {
              set $proxpass "http://lemmy";
            }
            proxy_pass $proxpass;

            rewrite ^(.+)/+$ $1 permanent;
            # Send actual client IP upstream
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }

        # backend
        location ~ ^/(api|pictrs|feeds|nodeinfo|.well-known) {
            proxy_pass "http://lemmy";
            # proxy common stuff
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";

            # Send actual client IP upstream
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }
    }
}