reading a packaged file in aws lambda package

Try this, it works for me:

'use strict'

let fs = require("fs");
let path = require("path");

exports.handler = (event, context, callback) => {
        // To debug your problem
        console.log(path.resolve("./readme.txt"));

        // Solution is to use absolute path using `__dirname`
        fs.readFile(__dirname +'/readme.txt', function (err, data) {
            if (err) throw err;
        });
};

to debug why your code is not working, add below link in your handler

console.log(path.resolve("./readme.txt"));

On AWS Lambda node process might be running from some other folder and it looks for readme.txt file from that folder as you have provided relative path, solution is to use absolute path.

What worked for me was the comment by Vadorrequest to use process.env.LAMBDA_TASK_ROOT. I wrote a function to get a template file in a /templates directory when I'm running it locally on my machine with __dirname or with the process.env.LAMBDA_TASK_ROOT variable when running on Lambda:

function loadTemplateFile(templateName) {
  const fileName = `./templates/${templateName}`
  let resolved
  if (process.env.LAMBDA_TASK_ROOT) {
    resolved = path.resolve(process.env.LAMBDA_TASK_ROOT, fileName)
  } else {
    resolved = path.resolve(__dirname, fileName)
  }
  console.log(`Loading template at: ${resolved}`)
  try {
    const data = fs.readFileSync(resolved, 'utf8')
    return data
  } catch (error) {
    const message = `Could not load template at: ${resolved}, error: ${JSON.stringify(error, null, 2)}`
    console.error(message)
    throw new Error(message)
  }
}