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1.1.0 • Public • Published

Moesif AWS Lambda Middleware

Middleware (NodeJS) to automatically log incoming API requests/responses from AWS Lambda functions and send to Moesif for error analysis. Designed for APIs that are hosted on AWS Lambda and using Amazon API Gateway as a trigger.

This middleware expects the Lambda proxy integration type. If you're using AWS Lambda with API Gateway, you are most likely using the proxy integration type.

Source Code on GitHub

Package on NPMJS

Express apps

Alternatively, if you're running the Express Framework on AWS Lambda and prefer to use Express middleware, Moesif has Express Middleware also available. The Express Middleware isn't specific to AWS lambda but won't capture AWS specific stuff like Trace Id.

How to install

npm install --save moesif-aws-lambda

How to use

The following shows how import the controllers and use:

1. Import the module:

// Import Modules
'use strict'
const moesif = require('moesif-aws-lambda');
const moesifOptions = {
    applicationId: 'Your Moesif application_id',
    identifyUser: function (event, context) {
        return event.requestContext.identity.cognitoIdentityId
exports.handler = function (event, context, callback) {
    callback(null, {
        statusCode: '200',
        body: JSON.stringify({key: 'hello world'}),
        headers: {
            'Content-Type': 'application/json',
exports.handler = moesif(moesifOptions, exports.handler);

2. Enter Moesif Application Id.

You can find your Application Id from Moesif Dashboard -> Top Right Menu -> App Setup

Repo file structure

  • lib/index.js the middleware lib
  • index.js sample AWS Lambda function using the middleware

Configuration options


Type: (event, context) => String identifyUser is a function that takes AWS lambda event and context objects as arguments and returns a userId. This helps us attribute requests to unique users. Even though Moesif can automatically retrieve the userId without this, this is highly recommended to ensure accurate attribution.

options.identifyUser = function (event, context) {
  // your code here, must return a string
  return event.requestContext.identity.cognitoIdentityId


Type: (event, context) => String getSessionToken a function that takes AWS lambda event and context objects as arguments and returns a session token (i.e. such as an API key).

options.getSessionToken = function (event, context) {
  // your code here, must return a string.
  return event.headers['Authorization'];


Type: (event, context) => String getTags is a function that takes AWS lambda event and context objects as arguments and returns a comma-separated string containing a list of tags. See Moesif documentation for full list of tags.

options.getTags = function (event, context) {
  // your code here. must return a comma-separated string.
  if (event.path.startsWith('/users') && event.httpMethod == 'GET'){
    return 'user'
  return 'random_tag_1, random_tag2'


Type: (event, context) => String getApiVersion is a function that takes AWS lambda event and context objects as arguments and returns a string to tag requests with a specific version of your API.

options.getApiVersion = function (event, context) {
  // your code here. must return a string.
  return '1.0.5'


Type: (event, context) => Boolean skip is a function that takes AWS lambda event and context objects as arguments and returns true if the event should be skipped (i.e. not logged)
The default is shown below and skips requests to the root path "/".

options.skip = function (event, context) {
  // your code here. must return a boolean.
  if (event.path === '/') {
    // Skip probes to home page.
    return true;
  return false


Type: MoesifEventModel => MoesifEventModel maskContent is a function that takes the final Moesif event model (rather than the AWS lambda event/context objects) as an argument before being sent to Moesif. With maskContent, you can make modifications to headers or body such as removing certain header or body fields.

options.maskContent = function(moesifEvent) {
  // remove any field that you don't want to be sent to Moesif.
  return moesifEvent;

EventModel format:

  "request": {
    "time": "2016-09-09T04:45:42.914",
    "uri": "https://api.acmeinc.com/items/83738/reviews/",
    "verb": "POST",
    "api_version": "1.1.0",
    "ip_address": "",
    "headers": {
      "Host": "api.acmeinc.com",
      "Accept": "*/*",
      "Connection": "Keep-Alive",
      "Content-Type": "application/json",
      "Content-Length": "126",
      "Accept-Encoding": "gzip"
    "body": {
      "items": [
          "direction_type": 1,
          "item_id": "fwdsfrf",
          "liked": false
          "direction_type": 2,
          "item_id": "d43d3f",
          "liked": true
  "response": {
    "time": "2016-09-09T04:45:42.914",
    "status": 500,
    "headers": {
      "Vary": "Accept-Encoding",
      "Pragma": "no-cache",
      "Expires": "-1",
      "Content-Type": "application/json; charset=utf-8",
      "Cache-Control": "no-cache"
    "body": {
      "Error": "InvalidArgumentException",
      "Message": "Missing field location"
  "user_id": "mndug437f43",
  "tags": "tag1, tag2"

For more documentation regarding what fields and meaning, see below or the Moesif Node API Documentation.

Fields Required Description
request.time Required Timestamp for the request in ISO 8601 format
request.uri Required Full uri such as https://api.com/?query=string including host, query string, etc
request.verb Required HTTP method used, i.e. GET, POST
request.api_version Optional API Version you want to tag this request with
request.ip_address Optional IP address of the end user
request.headers Required Headers of the request
request.body Optional Body of the request in JSON format
response.time Required Timestamp for the response in ISO 8601 format
response.status Required HTTP status code such as 200 or 500
request.ip_address Optional IP address of the responding server
response.headers Required Headers of the response
response.body Required Body of the response in JSON format

updateUser method

A method is attached to the moesif middleware object to update the users profile or metadata.

'use strict'
const moesif = require('moesif-aws-lambda');
const moesifOptions = {
    applicationId: 'Your Moesif application_id',
var moesifMiddleware = moesif(options);
var user = {
  userId: 'your user id',  // required.
  metadata: {
    email: 'user@email.com',
    name: 'George'
moesifMiddleware.updateUser(user, callback);

The metadata field can be any custom data you want to set on the user. The userId field is required.

Other integrations

To view more more documentation on integration options, please visit the Integration Options Documentation.


npm i moesif-aws-lambda

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