AWS Lambda function write to S3

Yes it is absolutely possible!

var AWS = require('aws-sdk');
function putObjectToS3(bucket, key, data){
    var s3 = new AWS.S3();
        var params = {
            Bucket : bucket,
            Key : key,
            Body : data
        }
        s3.putObject(params, function(err, data) {
          if (err) console.log(err, err.stack); // an error occurred
          else     console.log(data);           // successful response
        });
}

Make sure that you give your Lambda function the required write permissions to the target s3 bucket / key path by selecting or updating the IAM Role your lambda executes under.

IAM Statement to add:

{
    "Sid": "Stmt1468366974000",
    "Effect": "Allow",
    "Action": "s3:*",
    "Resource": [
        "arn:aws:s3:::my-bucket-name-goes-here/optional-path-before-allow/*"
    ]
}

Further reading:

• AWS JavaScript SDK
• The specific "Put Object" details

IAM Statement for serverless.com - Write to S3 to specific bucket

service: YOURSERVICENAME

provider:
  name: aws
  runtime: nodejs8.10
  stage: dev
  region: eu-west-1
  timeout: 60
  iamRoleStatements:
    - Effect: "Allow"
      Action:
       - s3:PutObject
      Resource: "**BUCKETARN**/*"
    - Effect: "Deny"
      Action:
        - s3:DeleteObject
      Resource: "arn:aws:s3:::**BUCKETARN**/*"

After long long time of silence-failing of 'Task timed out after X' without any good error message, i went back to the beginning, to Amazon default template example, and that worked!

> Lambda > Functions > Create function > Use a blueprints > filter: s3.

Here is my tweaked version of amazon example:

const aws = require('aws-sdk');
const s3 = new aws.S3({ apiVersion: '2006-03-01' });

async function uploadFileOnS3(fileData, fileName){
    const params = {
        Bucket:  "The-bucket-name-you-want-to-save-the-file-to",
        Key: fileName,
        Body: JSON.stringify(fileData),
    };

    try {
        const response = await s3.upload(params).promise();
        console.log('Response: ', response);
        return response;

    } catch (err) {
        console.log(err);
    }
};