AWS Lambda Node.js. mysql Error "Cannot enqueue Query after invoking quit" on second call onwards:

Question

I am currently creating an AWS Lambda resolver that utilizes Nodejs mysql library. Right now, my lambda is capable of executing a query to the database during the first invocation. However, on the subsequent invocations the error "Cannot enqueue Query after invoking quit" occurs. I am aware that it is something to do with the connection to the database but if I am not wrong, 'connection.query' should be making an implicit connection to the database. I am also calling the 'connection.end' within the callback. Could someone lend me a helping hand on this one?

Here is the Lambda index.js code:

/* Amplify Params - DO NOT EDIT
    API_SIMPLETWITTERCLONE_GRAPHQLAPIENDPOINTOUTPUT
    API_SIMPLETWITTERCLONE_GRAPHQLAPIIDOUTPUT
    API_SIMPLETWITTERCLONE_GRAPHQLAPIKEYOUTPUT
    AUTH_SIMPLETWITTERCLONEB1022521_USERPOOLID
    ENV
    REGION
Amplify Params - DO NOT EDIT */

const mysql = require("mysql");
// const util = require("util");
const config = require("./config.json");

const connection = mysql.createConnection({
  host: config.dbhost,
  user: config.dbuser,
  password: config.dbpassword,
  database: config.dbname,
});

// resolvers
const resolvers = {
  Query: {
    getAllUser: (event) => {
      return getAllUser();
    },
  },
};

function executeQuery(sql, params) {
  return new Promise((resolve, reject) => {
    const queryCallback = (error, results) => {
      if (error) {
        console.log("Error occured during query: " + error.message);
        connection.destroy();
        reject(error);
      } else {
        console.log("Connected to database and executed query");
        console.log("Results:", results);
        connection.end((err) => {
          if (err) {
            console.log("there was an error closing database:" + err.message);
          }
          console.log("database closed");
          resolve(results);
        });
      }
    };
    if (params) {
      connection.query(sql, [...params], (error, results) => {
        queryCallback(error, results);
      });
    } else {
      connection.query(sql, (error, results) => {
        queryCallback(error, results);
      });
    }
  });
}

async function getAllUser() {
  const sql = "SELECT * FROM User";
  try {
    const users = await executeQuery(sql);
    return users;
  } catch (error) {
    throw error;
  }
}

exports.handler = async (event) => {
  // TODO implement
  console.log("event", event);
  console.log('DB connection var', connection);
  const typeHandler = resolvers[event.typeName];
  if (typeHandler) {
    const resolver = typeHandler[event.fieldName];
    if (resolver) {
      try {
        return await resolver(event);
      } catch (error) {
        throw error;
      }
    }
  }
  throw new Error("Resolver not found");
};

Answer 1

You are ending your connection during the first invocation. As a result, the second invocation does not have that connection anymore.

If you create the connection during module import , do not end it in your invocation.

If you wish to end the connection during invocation , you have to create it during invocation as well.