Updating AWS S3 get object Lambda function to Node 22

One of the annoying things about software engineering is that working code doesn’t necessarily stay working. About eight years ago I wrote an Amazon Web Services Lambda Function using Node JS (I think version 10). Five years ago when the node version was end of life I updated it to Node 12 with no changes needed and it has been working ever since. I’ve had a few warnings from AWS about code relying on versions of node that are end-of-life but it was still working when I tested it.

exports.handler = (event, context, callback) => {
  var s3Bucket = "my-bucket-name";
  var key = "my-item-key";

  var AWS = require('aws-sdk');
  var s3 = new AWS.S3({region: 'eu-west-1'});

  var getFromAWS = function() {
    var params = {Bucket: s3Bucket, Key: key1};

    s3.getObject(params, function(err, data) {
      if(err) {
        itemJson = "[\"Error\":[\"Key not found\"]]";
        console.log(err, err.stack); // an error has happened on AWS
      }
      else {
        itemJson = data.Body.toString('UTF8');
      }
    }
    if (itemJson != "") {
      callback (null, {"key":key1, "data":itemJson});
    });
  };

  getFromAWS();
};

This week I needed to make a minor change to it, but in order to so I needed to update it to a later version of Node. As soon as I did so I got the following error.

Error: Cannot find Module ‘aws-sdk’

A quick google confirmed the issue, aws-sdk is no longer bundled as standard with Node on AWS lambda. This is slightly annoying as there are plenty of even recent articles which use the var AWS = require(‘aws-sdk’) syntax.

After reading up on it I decided it was probably time to bring the module fully up to date. In order to do that I would need to use AWS SDK version 3. Firstly I needed to import the required modules, and secondly I needed to use a different syntax to do the s3 Get Object command

import {S3Client, GetObjectCommand} from '@aws-sdk/client-s3';

var s3 = new S3Client({region: 'eu-west-1'});

const response = s3.send(new GetObjectCommand({
      Bucket: s3Bucket,
      Key: key,
    }));

Unfortunately as soon as I tried to make those changes I got a second error message.

Uncaught SyntaxError: Cannot use import statement outside a module

A quick search revealed that the simple solution to this is to ensure that the code was named index.mjs instead of index.js to show node that it was a module.

With these fixes in place I was able to rewrite the whole function.

Asynchronously Get Objects from S3 in parallel

I needed to be able to return two json files from S3. In order to keep the Lambda execution as short as possible I wanted to run the two commands in parallel. To achieve this I call the async getFromAWS function without using await, and then await both results in the highlighted line.

The full code of the working version is included below.

import {S3Client, GetObjectCommand} from '@aws-sdk/client-s3';

export const handler = async (event) => {
  var s3Bucket = "my-bucket-name"";
  var s3 = new S3Client({region: 'eu-west-1'});

  const getFromAWS = async(key) => { 
    const r = await s3.send(new GetObjectCommand({
      Bucket: s3Bucket,
      Key: key,
    }));
    
    const json = await r.Body.transformToString();
    return json;
  };

  var response;

  try {
    const firstJson = getFromAWS("my-item-key1");
    const secondJson = getFromAWS("my-item-key2");

    const result = [await firstJson, await secondJson];

    response = {
      "data1":JSON.parse(result[0]),
      "data2":JSON.parse(result[1])};
  } catch (e) {
    console.log(e);
    response = {"Error":"An Error Occurred"}
  }

  return response;
};