When to Open/Close Connection with Node-Postgres and Serverless

I'm migrating from AWS Aurora PG to Heroku PG and I'm currently refactoring my queries. Using the Node-Postgres library in my Serverless Framework API, I now have to manage opening and closing the connection, something I didn't have to do with the AWS-SDK.

I am following this article to setup my queries. Taken from the article:

let pgPool;

const setupPgPool = () => {
  // pgConfig is the host/user/password/database object
  pgPool = new pg.Pool(pgConfig);
};

module.exports.hello = async () => {
  if (!pgPool) {
    // "Cold start". Get Heroku Postgres creds and create connection pool.
    await setupPgPool();
  }
  // Else, backing container "warm". Use existing connection pool.

  try {
    const result = await pgPool.query('SELECT now()');

    // Response body must be JSON.
    return {
      statusCode: 200,
      body: JSON.stringify({
        output: {
          currTimePg: result.rows[0].now,
        },
      }),
    };
  } catch (e) {
    // Return error message in response body for easy debugging.
    // INSECURE - CHANGE FOR PROD
    return {
      statusCode: 500,
      body: JSON.stringify({
        error: e.message,
      }),
    };
  }
};

I'm trying to solve the issue of where to put the pgPool. My folder structure is like so:

src/
  controllers/
    auth/
      createUser.js
  models/
    authModel.js
    userModel.js

To dumb down my create createUser handler let's say it looks like this:

module.exports = (App) => {
  App.controllers.createAuth = async (event, context, cb) => {
    const body = JSON.parse(event.body)
    const { email, password } = body

    try {

      const hash = createHash(password)
        
      // Auth is a class that contains all my auth table read/write functions to the db
      const Auth = new App.Auth()
      const authRecordId = await Auth.createAuth(email, hash)

      // User is a class that contains all my user table read/write functions to the db
      const User = new App.User()
      await User.createUser(authRecordId)

      const token = createToken(authRecordId)

      return cb(null, utils.res(200, { token }))

    } catch (error) {
      return cb(null, utils.res(500, { message: 'There was an error. Please try again' } ))
    }
  }
}

Inside my authModel I have:

let pgPool

const setupPgPool = () => {
  // pgConfig is the host/user/password/database object
  pgPool = new pg.Pool(pgConfig)
}

Auth.prototype.createAuth = async (email, hash) => {
  const sql = `
    INSERT INTO auth (email, hash)
    VALUES (lower($1), $2)
    RETURNING id;
  `
  const values = [ email, hash ]

  try {
    if (!pgPool) {
      await setupPgPool()
    }

    const { rows } = await pgPool.query(sql, values)
    await pgPool.end()
    return rows[0].id
  } catch (err) {
    throw err
  }
}

The userModal query looks very similar (setup pgPool, run query, end connection, return data). The issue is pgPool never exists and I always need to await it before running the query. I also need to run await pgPool.end() otherwise my queries will hang. Is this the best practice, as the article suggests, in a Serverless Framework API?

Lastly, should I instead open the connection my handler and pass pgPool as an argument to my models? That way if I have to make more than one query to my database I don't have to await setupPgPool every time I want to read/write from the database?

EDIT: I was refactoring my first handler as I was writing this. After implementing what I used in the post, I am now running into this error: Cannot use a pool after calling end on the pool. Seems to be because I am closing the connection.

EDIT 2: Commented out the await pgPool.end() lines and now my calls hang again.. not really sure what to do..

I solved my issue by the following:

• I started using "serverless-postgres" instead of "pg-node"
• But, I think this is the real reason, I STOPPED USING THE CALLBACK PARAMETER

I was going insane wondering how this was working for everyone else but me.

1. Started an entire new sls project and got it to return "hello"
2. Installed serverless-postgres, connected to my database but still return hello without any errors
3. Run this code:

  await client.connect();
  const result = await client.query(`SELECT 1+1 AS result`);
  await client.clean();
  return {
    body: JSON.stringify({ message: result.rows[0] }),
    statusCode: 200
  }

4. Tried to run that code on my project. Didn't work.
5. Compared my handler to this new projects handler and realized they just return instead of using the third parameter, callback.

Not sure when Serverless did away with callback and just returned (I guess I haven't been keeping up with the latest) but wrapping with callback was causing issues. Simply returning and removing callback fixed everything.

If you are having issues too I recommend you follow what I did. Get an external version of the basics working and try to slowly integrate it into your app.