How to Write and Read files to Lambda-AWS with Node.js - amazon-web-services

Question

I am trying to write and read to /temp dir in lambda during function execution, I know the best way would be to use S3, but for this project, I have to use node file system
const fs = require('fs');
exports.handler = async (event) => {
const path = '/tem/hi.json';
const write = (file) => {
fs.writeFile(file, "Hello World!", function(err) {
if (err) return console.log(err);
return {
statusCode:200,
body:JSON.stringify('data was written')
};
});
};
return write(path);
};

Answer 1

You have a typo on your file path.
Change
const path = '/tem/hi.json';
to
const path = '/tmp/hi.json';
Also, fs.writeFile is an asynchronous operation. Promisify it so you can await on it:
const write = file => {
return new Promise((res, rej) => {
fs.writeFile(file, JSON.stringify({ message: 'hello world' }), (err) => {
if (err) {
return rej(err)
}
return res({
statusCode: 200,
body: JSON.stringify({message: 'File written successfully'})
})
})
})
}
Finally, on your client (last line of your handler), just invoke it like this:
return await write(path)

Answer 2

fs.writeFile is an asynchronous operation, so the lambda ends before it finishes. You can use fs.writeFileSync to block the lambda execution until the file is sucessfuly written:
const write = (file) => {
try {
fs.writeFileSync(file, "Hello World!");
return {
statusCode: 200,
body: 'data was written'
};
} catch (err) {
console.log(err);
return {
statusCode: 500,
body: 'data was not written'
};
}
};