AWS Custom Lambda Layer

Lambda Layer:
Used to share code between functions

Package below into a Lambda layer:
1. Set of reusable functions that can be used across Lambda's.
2. npm module that can be used across Lambda's.

Consider we have set of reusable functions like below in a file named reusable.js:

const getCountryCode = function(countryName) {
  let countryCodeMapping = {
    "India" : "IN",
    "United States of America" : "USA",
    "United Kingdom" : "UK"  
  };
  return countryCodeMapping[countryName];
};
module.exports = { getCountryCode }

Folder structure:

nodejs (FolderName)
    reusableCodeFiles.js
    package.json
    node_modules

How to zip (Windows):

Right click the nodejs folder -> 7-Zip -> Add to "nodejs.zip"
nodejs - foldername
nodejs.zip

How to use the Layer reusable code from Lambda:

const reusableCode = require('/opt/nodejs/reusable');
// reusable is the name of file (.ie. reusable.js) inside nodejs zip file 

exports.handler = async (event) => {
    console.log(reusableCode .getCountryCode("India"));
        //Logs IN   
};