Chaining Lambda Functions using the Serverless Framework — Part 1

3 min readNov 9, 2017

In this article I want to show how to chain AWS Lambda Functions which basically means calling a Lambda Function from another Lambda Function using the Serverless Framework.

TL;DR

Here you can find a GitHub repository if you want a quick start.

MeBNoah/serverless-lambda-chaining

Contribute to serverless-lambda-chaining development by creating an account on GitHub.

github.com

Prerequisites

At least for the prerequisites you should check my previous article.

Create Lambda Function

Now we are good to go, so lets create a new project using the Serverless Framework

Bootstrap Project

First create a project

serverless create --template aws-nodejs --path lambda-chaining

Move to the generated project and a dependency to the aws-sdk module

npm install --save aws-sdk

Prepare Environment

The Serverless Framework allows to set AWS IAM access rights, which we are going to need in order to grant rights for invoking a Lambda Function from another Lambda Function. Paste the following in your serverless.yml

service: lambda-chaining
provider:
  name: aws
  runtime: nodejs6.10
  iamRoleStatements:
    - Effect: Allow
      Action:
        - lambda:InvokeFunction
        - lambda:InvokeAsync
      Resource: "*"

Define Lambda Functions

Finally we can define two Lambda Functions, therefore we create the following functions in the handler.js

'use strict'
var aws = require('aws-sdk')

module.exports.hello = (event, context, callback) => {
  var lambda = new aws.Lambda()
  var opts = {
    FunctionName: 'lambda-chaining-dev-ciao'
  }

  lambda.invoke(opts, function (err, data) {
    if (err) {
      console.log('error : ' + err)
      callback(err, null)
    } else if (data) {
      const response = {
        statusCode: 200,
        body: JSON.parse(data.Payload)
      }
      callback(null, response)
    }
  })
}

module.exports.ciao = (event, context, callback) => {
  callback(null, { message: 'ciao world!' })
}

For invoking another Lambda Function we have to just specify the name of the Lambda Function which should be invoked. The scheme is the following: service-stage-function. You can see that in line 7 of the handler.js file.

Define handler

One step is left and that is to connect our functions to the respective Lambda Function handlers in the serverless.yml

functions:
  hello:
    handler: handler.hello
  ciao:
    handler: handler.ciao

Deploy Lambda Functions

At this point we could deploy our Lambda Functions

serverless deploy -v

You should see verbose output and if everything went fine you can see your Lambda Functions in the respective AWS console view. Just be sure to select the right region.

Invoke Lambda Function

Now you can invoke our first Lambda Function which should call the second one and return the following string “ciao world!”

serverless invoke -f hello -l

Next Steps

Congratulations, you have successfully created, deployed and invoked a Lambda Function which calls another Lambda Function. A next step could be to invoke a Step Function out of Lambda Function which is quite similar to invoking a Lambda Function out of another one. Instead of using

...  
  var lambda = new aws.Lambda()
  var opts = {
    FunctionName: 'lambda-chaining-dev-ciao'
  }

  lambda.invoke(opts, function (err, data) {
...

You would have to use something like

...  
  var stepfunctions = new aws.StepFunctions()
  var params = {    
    stateMachineArn: <step_function_arn>, 
    input: JSON.stringify({})  
  }  
  stepfunctions.startExecution(params, function (err, data) {
...

One use case for this setup could be if you want to invoke a step function through an AWS API Gateway and want validate your requests against the API Gateway. Validation then would be done in the “Proxy” Lambda which then Invokes the Step Function.

Note that this time we cannot just specify the the name of the Step Function like it was the case for invoking the Lambda. Getting the ARN of the Step Function is not that easy, you can read about it in my dedicated article about referencing Lambda or Step Functions, or having a look at the following GitHub repository if you want to directly walk through code.

MeBNoah/serverless-lambda-stepfunction

Contribute to serverless-lambda-stepfunction development by creating an account on GitHub.