Deployment through app engine, cloud sql database, problem connecting with server code, doesn't connect

Question

I made a client-server side app using React.js and Expres.js. I also used a local database made on mysql workbench.

I want to deploy my app to app-engine on google cloud, for this purpose I exported my db and now it is on the cloud.

The problem arises when I want ot deploy the app. The client sode shows, but whenever I try to do any function the app crashes and I get an error CONNECTION REFUSED.

So far I have tried:

• using the app engine template from the documentation
• using keys
• using solutions from gemini, copilot and chatgpt

This is my app.yaml

  runtime: nodejs18
env: standard
instance_class: F2

handlers:
  # Catch all handler to index.html
  - url: /.*
    script: auto
    secure: always
    redirect_http_response_code: 301

automatic_scaling:
  target_cpu_utilization: 0.65
  min_instances: 1
  max_instances: 10

env_variables:
  INSTANCE_CONNECTION_NAME: "hidden"
  DB_PRIVATE_IP: ,
  INSTANCE_HOST: "hidden"
  DB_PORT: "3306"
  DB_USER: "root"
  DB_PASS: "************"
  DB_NAME: "social_media"

vpc_access_connector:
  name: projects/hidden

// import userRoutes from "./routes/users.js";
// import postRoutes from "./routes/posts.js";
// import likeRoutes from "./routes/likes.js";
// import commentRoutes from "./routes/comments.js";
// import relationshipRoutes from "./routes/relationships.js";
// import authRoutes from "./routes/auth.js";
// import cookieParser from "cookie-parser";
// import cors from "cors";
// import multer from "multer";
// import Express from "express";
// const app = Express();

// //middlewares
// app.use((req, res, next) => {
//   res.header("Access-Control-Allow-Credentials", true);
//   res.header("Access-Control-Allow-Origin", "*");
//   res.header("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
//   res.header("Access-Control-Allow-Headers", "Content-Type");
//   next();
// });
// app.use(Express.json());
// app.use(
//   cors({
//     origin: "http://localhost:3000",
//   })
// );
// app.use(cookieParser());

// const storage = multer.diskStorage({
//   destination: function (req, file, cb) {
//     cb(null, "../client/public/upload");
//   },
//   filename: function (req, file, cb) {
//     cb(null, Date.now() + file.originalname);
//   },
// });

// const upload = multer({ storage: storage });

// app.post("/api/upload", upload.single("file"), (req, res) => {
//   const file = req.file;
//   console.log("Received file:", file);
//   res.status(200).json(file.filename);
// });

// app.use("/api/users", userRoutes);
// app.use("/api/posts", postRoutes);
// app.use("/api/likes", likeRoutes);
// app.use("/api/comments", commentRoutes);
// app.use("/api/relationships", relationshipRoutes);
// app.use("/api/auth", authRoutes);

// app.listen(8800, () => {
//   console.log("API working!!");
// });

// /*const {Sequelize} = require('sequelize');

// // Create a new Sequelize instance.
// const sequelize = new Sequelize('social_media', 'root', 'password', {
//   host: '/cloudsql/third-current-418819:us-central1:systems3db',
//   dialect: 'mysql',
// });

// // Test the connection to the database.
// sequelize
//   .authenticate()
//   .then(() => {
//     console.log('Connection to the database has been established successfully.');
//   })
//   .catch(err => {
//     console.error('Unable to connect to the database:', err);
//   });
//  */

import userRoutes from "./routes/users.js";
import postRoutes from "./routes/posts.js";
import likeRoutes from "./routes/likes.js";
import commentRoutes from "./routes/comments.js";
import relationshipRoutes from "./routes/relationships.js";
import authRoutes from "./routes/auth.js";
import cookieParser from "cookie-parser";
import cors from "cors";
import multer from "multer";
import Express from "express";
import mysql from "mysql2/promise";
const app = Express();

// Get the environment variables
const {
  INSTANCE_HOST,
  DB_PORT,
  DB_USER,
  DB_PASS,
  DB_NAME,
  INSTANCE_CONNECTION_NAME,
} = process.env;

// Create a connection pool
const pool = mysql.createPool({
  host: INSTANCE_HOST,
  user: DB_USER,
  database: DB_NAME,
  password: DB_PASS,
  port: DB_PORT,
  socketPath: /cloudsql/${INSTANCE_CONNECTION_NAME},
  waitForConnections: true,
  connectionLimit: 10,
  queueLimit: 0,
});

// Now you can use the pool to query your database
app.post("/users", async (req, res) => {
  try {
    const [rows, fields] = await pool.execute("SELECT * FROM users");
    res.json(rows);
  } catch (err) {
    res.status(500).json(err);
  }
});

// etc.

//middlewares
app.use((req, res, next) => {
  res.header("Access-Control-Allow-Credentials", true);
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
  res.header("Access-Control-Allow-Headers", "Content-Type");
  next();
});
app.use(Express.json());
app.use(
  cors({
    origin: "http://localhost:3000",
  })
);
app.use(cookieParser());

const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, "../public/upload");
  },
  filename: function (req, file, cb) {
    cb(null, Date.now() + file.originalname);
  },
});

const upload = multer({ storage: storage });

app.post("/api/upload", upload.single("file"), (req, res) => {
  const file = req.file;
  console.log("Received file:", file);
  res.status(200).json(file.filename);
});

app.use("/api/users", userRoutes);
app.use("/api/posts", postRoutes);
app.use("/api/likes", likeRoutes);
app.use("/api/comments", commentRoutes);
app.use("/api/relationships", relationshipRoutes);
app.use("/api/auth", authRoutes);
const PORT = process.env.PORT || 8800;
app.listen(PORT, () => {
  console.log(API working P:${PORT}!!);
});