nginx.conf

worker_processes  1;
# error_log  logs/debug.log debug;
user root;
events {
    worker_connections  1024;
}

env OPENAI_API_HOST;
env OPENAI_MODEL;
env OPENAI_VISION_API_HOST;
env OPENAI_VISION_MODEL;
env OPENAI_EMBEDDING_API_HOST;
env OPENAI_EMBEDDING_MODEL;

http {
    map $http_upgrade $connection_upgrade {
        default upgrade;
        ''      close;
    }
    fastcgi_intercept_errors on;
    include       mime.types;
    default_type  application/octet-stream;
    sendfile        on;
    keepalive_timeout  65;

    client_max_body_size 20m;
    client_body_buffer_size 20m;
    proxy_buffer_size 20m;
    proxy_buffers 4 20m;
    proxy_busy_buffers_size 20m;
    proxy_request_buffering on;
    proxy_http_version 1.1;
    proxy_set_header Connection "";

    resolver 8.8.8.8;

    # lua_code_cache off;
    lua_need_request_body on;
    # cache for discovery metadata documents
    lua_shared_dict discovery 1m;
    # cache for JWKs
    lua_shared_dict jwks 1m;
    real_ip_header     X-Forwarded-For;
    real_ip_recursive on;
    lua_package_path '/opt/app/?.lua;;';
    lua_ssl_verify_depth 3;

    server {
        listen    80;
#         listen    443 ssl;
        server_name  127.0.0.1;
        charset utf-8;
        default_type text/html;

        # lua_code_cache off;
        set $session_check_ssi off;
        set $session_name model_api_proxy_session;
        set $session_secret 623q4hR325t36VsCD3g567922IC0073T;

        expires           0;
        add_header        Cache-Control private;

        location / {
            proxy_redirect off;
            proxy_set_header  Host  $http_host;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";
            proxy_http_version 1.1;
            proxy_cache off;
            proxy_buffering off;
            chunked_transfer_encoding on;
            tcp_nopush on;
            tcp_nodelay on;
            keepalive_timeout 300;

            if ($request_method = POST ) {
                set $upstream '';
                access_by_lua '
                    local OPENAI_MODELS = {
                        ["gpt-3.5-turbo"] = {model = os.getenv("OPENAI_MODEL"), host = os.getenv("OPENAI_API_HOST")},
                        ["gpt-4o-mini"] = {model = os.getenv("OPENAI_VISION_MODEL"), host = os.getenv("OPENAI_VISION_API_HOST")},
                        ["text-embedding-ada-002"] = {model = os.getenv("OPENAI_EMBEDDING_MODEL"), host = os.getenv("OPENAI_EMBEDDING_API_HOST")}
                    }

                    ngx.req.read_body()
                    local data = ngx.req.get_body_data()

                    if data then
                        local json = require("cjson")
                        local decoded_data = json.decode(data)
                        
                        if decoded_data and OPENAI_MODELS[decoded_data["model"]] then
                            local selected_model = OPENAI_MODELS[decoded_data["model"]]
                            decoded_data["model"] = selected_model.model
                            data = json.encode(decoded_data)
                            
                            ngx.req.set_body_data(data)
                            ngx.req.set_header("Content-Length", string.len(data))
                            ngx.var.upstream = selected_model.host
                        end
                    end
                ';
                proxy_pass http://$upstream;
            }
            if ($request_method = GET ) {
                set $upstream '';
                access_by_lua '
                    ngx.var.upstream = os.getenv("OPENAI_API_HOST")
                ';
                proxy_pass http://$upstream;
            }
        }

    }
}