AWS Lamda/API Gateway Every Second Call Results in Internal Server Error - amazon-web-services

Question

I'm need to 'Nodejs' and 'Serveless'. I've created a 'Serverless' API and deployed to AWS. Everything works as expected. The issue i have and i can't seem to find anything about this is, on every second call i get an internal server error. the first call is, returns data as expected.
I've deployed to AWS only in a dev stage. I'm wondering if there is some configuration i'm missing or something?
If you need the 'Serverless' config or code examples i can provide.
Thanks.
ANSWER
I think there was an issue with the DB call not returning data in time for the callback, therefore i was finding inconsistent results.
So basically what i did was create a Database class returning Promises like so...
'use strict';
const mysql = require('mysql');
/**
* Database
*/
class Database {
constructor(config) {
if (!this.dbConnection) {
console.log('connect to DB');
this.dbConnection = mysql.createPool(config);
this.dbConnection.on('connection', (connection) => {
console.info('Connection Made!');
});
}
}
query(sql, args) {
return new Promise((resolve, reject) => {
this.dbConnection.query(sql, args, (err, rows) => {
if (err) {
reject(err);
}
resolve(rows);
})
});
}
close() {
return new Promise((resolve, reject) => {
this.dbConnection.end((error) => {
if (error) {
reject(error);
}
resolve();
});
});
}
}
module.exports = Database;
So when i made my query there was a result ready for the callback.
'use strict';
const Database = require('./lib/Database');
const {successResponse, errorResponse} = require('./lib/response');
const CategoryResource = require('./resource/Category');
module.exports.list = (event, context, callback) => {
let sql = 'SELECT * FROM categories AS c WHERE c.company_id = ? AND c.parent_id IS NULL AND c.status = 1 LIMIT ?, ?;';
const company = parseInt(event.queryStringParameters.company);
let page = 1;
let limit = 20;
if (null != event.queryStringParameters) {
if ('page' in event.queryStringParameters) {
page = parseInt(event.queryStringParameters.page);
}
if ('limit' in event.queryStringParameters) {
limit = parseInt(event.queryStringParameters.limit);
}
}
let start = (page - 1) * limit;
if (isNaN(company)) {
callback(null, errorResponse(400, 'Company ID Required', 'Parameter company_id is required.', []));
return;
}
let Category = new Database();
let categoryResource = [];
Category
.query(sql, [company, start, limit])
.then(response => {
Category.close();
response.forEach((category) => {
categoryResource.push(CategoryResource(category));
});
callback(null, successResponse(200, {
"total": response.length,
"perPage": limit,
"currentPage": page,
"data": categoryResource
}));
})
.catch((error) => {
callback(null, errorResponse(error.code, error.sqlMessage, error.sql, {
code: error.errno,
field: error.sqlMessage,
message: error.sqlMessage
}));
Category.close();
});
};
I hope that helps anyone that may have run into the same issue.

Answer 1

If every other time you get an internal server error, that means your code is syntactically sound but has some sort of logic error. It's impossible to help without example code, but some of the more common errors I've seen that only sometimes occur can be:
race conditions (if you're doing parallel access of the same array, for example)
array access errors (length+1 instead of length-1, less-than-zero, or your iterators are jumping someplace in memory they shouldn't)
simply mentioning the wrong variable (putting an i instead of a j, for example)
Unfortunately, without specific examples, the best we can offer is wild speculation and personal experience. Have you tried looking at AWS's CloudWatch and what it says about your execution? There should be some errors logged in there too.

Answer 2

I think there was an issue with the DB call not returning data in time for the callback, therefore i was finding inconsistent results.
So basically what i did was create a Database class returning Promises like so...
'use strict';
const mysql = require('mysql');
/**
* Database
*/
class Database {
constructor(config) {
if (!this.dbConnection) {
console.log('connect to DB');
this.dbConnection = mysql.createPool(config);
this.dbConnection.on('connection', (connection) => {
console.info('Connection Made!');
});
}
}
query(sql, args) {
return new Promise((resolve, reject) => {
this.dbConnection.query(sql, args, (err, rows) => {
if (err) {
reject(err);
}
resolve(rows);
})
});
}
close() {
return new Promise((resolve, reject) => {
this.dbConnection.end((error) => {
if (error) {
reject(error);
}
resolve();
});
});
}
}
module.exports = Database;
So when i made my query there was a result ready for the callback.
'use strict';
const Database = require('./lib/Database');
const {successResponse, errorResponse} = require('./lib/response');
const CategoryResource = require('./resource/Category');
module.exports.list = (event, context, callback) => {
let sql = 'SELECT * FROM categories AS c WHERE c.company_id = ? AND c.parent_id IS NULL AND c.status = 1 LIMIT ?, ?;';
const company = parseInt(event.queryStringParameters.company);
let page = 1;
let limit = 20;
if (null != event.queryStringParameters) {
if ('page' in event.queryStringParameters) {
page = parseInt(event.queryStringParameters.page);
}
if ('limit' in event.queryStringParameters) {
limit = parseInt(event.queryStringParameters.limit);
}
}
let start = (page - 1) * limit;
if (isNaN(company)) {
callback(null, errorResponse(400, 'Company ID Required', 'Parameter company_id is required.', []));
return;
}
let Category = new Database();
let categoryResource = [];
Category
.query(sql, [company, start, limit])
.then(response => {
Category.close();
response.forEach((category) => {
categoryResource.push(CategoryResource(category));
});
callback(null, successResponse(200, {
"total": response.length,
"perPage": limit,
"currentPage": page,
"data": categoryResource
}));
})
.catch((error) => {
callback(null, errorResponse(error.code, error.sqlMessage, error.sql, {
code: error.errno,
field: error.sqlMessage,
message: error.sqlMessage
}));
Category.close();
});
};
I hope that helps anyone that may have run into the same issue.