nginx.conf

events {
    worker_connections  1024;
}

http {
    lua_shared_dict room_cache 10m;
    resolver 127.0.0.11 ipv6=off;

    limit_req_zone $binary_remote_addr zone=ws_rate_limit:10m rate=10r/s;
    limit_req_zone $binary_remote_addr zone=api_rate_limit:10m rate=5r/s;

    upstream app_1 {
        server app_1:8080;
    }

    upstream app_2 {
        server app_2:8081;
    }

    server {
        listen 80;
        root /dev/null;

        error_page 400 404 500 503 504 /error.html;
        
        location = /error.html {
            root /usr/local/openresty/nginx/html;
            internal;
            ssi on;
        }

        location /create-room {
            limit_req zone=api_rate_limit burst=10 nodelay;
            proxy_pass http://app_1;
        }

        location /join-room {
            limit_req zone=api_rate_limit burst=10 nodelay;
            proxy_pass http://app_1;
        }

        location /health1 {
            proxy_pass http://app_1;
        }

        location /health2 {
            proxy_pass http://app_2;
        }

        location /ws {
            limit_req zone=ws_rate_limit burst=20 nodelay;
            access_log /usr/local/openresty/nginx/logs/access.log combined buffer=512k flush=1s;
            error_log /usr/local/openresty/nginx/logs/error.log notice;
            
            set $backend "";
            set $room_id $arg_roomId;

            access_by_lua_block {
                local room_cache = ngx.shared.room_cache
                local redis = require "resty.redis"
                local room_id = ngx.var.room_id

                local instance = room_cache:get('room:' .. room_id)

                if not instance then
                    local red = redis:new()
                    red:set_timeout(1000)

                    local ok, err = red:connect("redis", 6379)
                    if not ok then
                        ngx.log(ngx.ERR, "Redis connection failed: ", err)
                        ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
                    end

                    instance, err = red:get('room:' .. room_id .. ':affinity')
                    if not instance then
                        ngx.log(ngx.ERR, "Redis GET failed: ", err)
                        ngx.exit(ngx.HTTP_BAD_REQUEST)
                    end

                    if instance == "" then
                        ngx.log(ngx.ERR, "Empty room affinity")
                        ngx.exit(ngx.HTTP_NOT_FOUND)
                    end

                    room_cache:set('room:' .. room_id, instance, 60)
                    red:close()
                end

                if instance == "instance_1" then
                    ngx.var.backend = "app_1"
                elseif instance == "instance_2" then
                    ngx.var.backend = "app_2"
                else
                    ngx.log(ngx.ERR, "Invalid instance: ", instance)
                    ngx.exit(ngx.HTTP_NOT_FOUND)
                end
            }

            proxy_pass http://$backend;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "Upgrade";
        }
    }
}