Can an AWS Lambda function call another

Question

I have 2 Lambda functions - one that produces a quote and one that turns a quote into an order. I'd like the Order lambda function to call the Quote function to regenerate the quote, rather than just receive it from an untrusted client.

I've looked everywhere I can think of - but can't see how I'd go about chaining or calling the functions...surely this exists!

Answer 1

I found a way using the aws-sdk.

var aws = require('aws-sdk');
var lambda = new aws.Lambda({
  region: 'us-west-2' //change to your region
});

lambda.invoke({
  FunctionName: 'name_of_your_lambda_function',
  Payload: JSON.stringify(event, null, 2) // pass params
}, function(error, data) {
  if (error) {
    context.done('error', error);
  }
  if(data.Payload){
   context.succeed(data.Payload)
  }
});

You can find the doc here: http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/Lambda.html

Answer 2

You should chain your Lambda functions via SNS. This approach provides good performance, latency and scalability for minimal effort.

Your first Lambda publishes messages to your SNS Topic and the second Lambda is subscribed to this topic. As soon as messages arrive in the topic, second Lambda gets executed with the message as it's input parameter.

See Invoking Lambda functions using Amazon SNS notifications.

You can also use this approach to Invoke cross-account Lambda functions via SNS.

Answer 3

here's a sample code for python,

from boto3 import client as boto3_client
from datetime import datetime
import json

lambda_client = boto3_client('lambda')

def lambda_handler(event, context):
    msg = {"key":"new_invocation", "at": datetime.now()}
    invoke_response = lambda_client.invoke(FunctionName="another_lambda_",
                                           InvocationType='Event',
                                           Payload=json.dumps(msg))
    print(invoke_response)

Btw, you would need to add a policy like this to your lambda role as well

   {
        "Sid": "Stmt1234567890",
        "Effect": "Allow",
        "Action": [
            "lambda:InvokeFunction"
        ],
        "Resource": "*"
    }

Answer 4

Since this question was asked, Amazon has released Step Functions (https://aws.amazon.com/step-functions/).

One of the core principles behind AWS Lambda is that you can focus more on business logic and less on the application logic that ties it all together. Step functions allows you to orchestrate complex interactions between functions without having to write the code to do it.

Answer 5

I was looking at cutting out SNS until I saw this in the Lambda client docs (Java version):

Client for accessing AWS Lambda. All service calls made using this client are blocking, and will not return until the service call completes.

So SNS has an obvious advantage: it's asynchronous. Your lambda won't wait for the subsequent lambda to complete.

Answer 6

This solution is done using boto3 and Python:

import boto3
import json

invokeLambda = boto3.client('lambda', region_name='eu-west-1')

def lambda_handler(event, context):
    invokeLambda.invoke(FunctionName = 'function_name', InvocationType = 'RequestResponse', Payload = json.dumps(event))

    return True

Answer 7

Amazon has introduced steps functions in AWS lambda in 2016. I think, now it's more convenient to use steps function as it's really easy to use them. You can build a state machine with two lambda functions as:

• to produces a quote
• turns a quote into an order

You can easily do that as below:

Here you can have first state for produces a quote and another to turns into order

{
  Comment: "Produce a quote and turns into an order",
  StartAt: "ProduceQuote",
  States: {
    ProduceQuote: {
      "Type": Task,
      "Resource": "arn:aws:lambda:us-east-1:123456789012:function:ProduceQuote",
      "next": TurnsToOrder
    }
    TurnsToOrder: {
      Type: Task,
      Resource: "arn:aws:lambda:us-east-1:123456789012:function:ProduceQuote",
      end: true
    }
  }
}

Steps functions makes it really easy to write multiple lambda functions and run in sequence or in parallel. You can get more information about lambda steps functions here: Steps Functions

Answer 8

I was working with the answer provided by blueskin but I could not read the Payload response because the InvocationType='Event' is async, so I changed as InvocationType='RequestResponse' and now all works good.

Answer 9

In java, we can do as follows :

AWSLambdaAsync awsLambdaAsync = AWSLambdaAsyncClientBuilder.standard().withRegion("us-east-1").build();

InvokeRequest invokeRequest = new InvokeRequest();
invokeRequest.withFunctionName("youLambdaFunctionNameToCall").withPayload(payload);

InvokeResult invokeResult = awsLambdaAsync.invoke(invokeRequest); 

Here, payload is your stringified java object which needs to be passed as Json object to another lambda in case you need to pass some information from calling lambda to called lambda.

Answer 10

You might be able to make use of the Async.js Waterfall feature - see the bottom part of the big code chunk in Step 3 of this document for an example:

https://aws.amazon.com/blogs/compute/better-together-amazon-ecs-and-aws-lambda/

Answer 11

You can invoke lambda function directly (at least via Java) by using AWSLambdaClient as described in the AWS' blog post.

Answer 12

I'm having the same problem but the Lambda function that I implement will insert an entry in DynamoDB, so my solution uses DynamoDB Triggers.

I make the DB invoke a Lambda function for every insert/update in the table, so this separates the implementation of two Lambda functions.

Documentation is here: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Streams.Lambda.html

Here is a guided walkthrough: https://aws.amazon.com/blogs/aws/dynamodb-update-triggers-streams-lambda-cross-region-replication-app/

Answer 13

Kind of a roundabout solution but I just call the API endpoint for my lambda functions when I need to chain them. This allows you to decide while coding if you want them to be asynchronous or not.

In case you don't want to setup a POST request you can just setup a simple GET request with a couple, or none at all, query string parameters for easy event passing.

-- Edit --

See: https://docs.aws.amazon.com/apigateway/api-reference/making-http-requests/

and: http://docs.aws.amazon.com/lambda/latest/dg/with-on-demand-https-example.html

Answer 14

You can set AWS_REGION environment.

assert(process.env.AWS_REGION, 'Missing AWS_REGION env (eg. ap-northeast-1)');
const aws = require('aws-sdk');
const lambda = new aws.Lambda();