I am trying to connect an external (not AWS) MySql server from an AWS Lambda function written in Node.js using nodejs14.x environment, but the connect() callback is not called.
I am been struggling with this problem since days, there are a lot of references to similar issues but I really tried all possible permutations of solutions I found.
I am deploying with SAM and testing both on local machine and on real AWS.
Here is the sample code of the lambda helper
const mysql = require('mysql');
exports.helloFromLambdaHandler = async () => {
const message = 'Hello from Lambda!';
console.info(`${message}`);
var sql = "SELECT 1+? AS sum";
var values = [1];
console.log("Doing createConnection");
const connection = mysql.createConnection({
/* my connection data */
});
console.log("Doing connect");
connection.connect( (err) => {
console.log("Inside connection callback");
console.log('connected as id ' + connection.threadId);
if(!err) {
console.log("DB connected, thread id is " + connection.threadId);
console.log("Doing query");
connection.query(sql, values, (err, result, values) => {
console.log("Inside query callback");
if(!err) {
console.log("Query ok!");
console.log(result);
connection.end();
} else {
console.log("Error executing query: " + err.message);
}
});
} else {
console.log("Error connecting db: "+ err.message);
}
});
console.log ("Returning...");
return message;
}
The log is
Hello from Lambda!
Doing createConnection
Doing connect
Returning...
The expected behaviour is that after "Returning..." I should see the log "Inside connection callback" then "Inside query callback" and then "Query ok!".
Instead the callback of connect() appears not invoked.
I know that I can call query() directly skipping connect() but also doing so I encounter same issue.
Any clue?
Thank you!
SOLUTION
As suggested by the accepted answer, returning a promise is the solution to let Node complete all the queue. Unfortunately it's not possible to complete the Lambda and leave it running in background in a safe manner, for what I understand.
I am investigating alternative solutions such as:
- mysql2 library which supports promises natively
- serverless-mysql npm package which handles shared db connections
Below the running demo code
const mysql = require('mysql');
exports.helloFromLambdaHandler = async (event, context) => {
const message = 'Hello from Lambda!';
console.info(`${message}`);
var sql = "SELECT 1+? AS sum";
var values = [1];
console.log("Doing createConnection");
const connection = mysql.createConnection({
/* my connection data */
});
console.log("Doing query");
const promise = new Promise( (resolve, reject) => {
connection.query(sql, values, (err, result, values) => {
console.log("Inside query callback");
if(!err) {
console.log("Query ok!");
console.log(result);
connection.end();
resolve(message);
} else {
console.log("Error executing query: " + err.message);
reject(err);
}
});
});
console.log ("Returning...");
return promise;
}
