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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

There are a lot of answers  but none is stressing that calling another lambda function is not recommended solution for synchronous calls and the one that you should be using is really Step Functions Reasons why it is not recommended solution   you are paying for both functions your code is responsible for retrials  You can also use it for quite complex logic  such as parallel steps and catch failures  Every execution is also being logged out which makes debugging much simpler

User · Answer

You can trigger Lambda functions directly from other Lambda functions directly in an asynchronous manner  https   docs aws amazon com lambda latest dg invocation-async html invocation-async-destinations

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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

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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

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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

User · Answer

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

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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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

Others pointed out to use SQS and Step Functions  But both these solutions add additional cost  Step Function state transitions are supposedly very expensive    AWS lambda offers some retry logic  Where it tries something for 3 times  I am not sure if that is still valid when you trigger it use the API

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

Here is the python example of calling another lambda function and gets its response  There is two invocation type  RequestResponse  and  Event   Use  RequestResponse  if you want to get the response of lambda function and use  Event  to invoke lambda function asynchronously  So both ways asynchronous and synchronous are available         lambda response   lambda client invoke                  FunctionName   lambda name                  InvocationType    RequestResponse                   Payload   json dumps input                        resp str   lambda response  Payload   read       response   json loads resp str

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