Is there a way to trigger AWS lambda by another lambda and SQS?

Question

Lets say I have two lambdas: A & B. A is listening to an SQS.

I want the flow to be as followed:

A message arrived to the SQS.
Lambda A pulls the message and starts working on it.
After lambda A started, lambda B also takes the message and does other things. But lambda B must start after A has already started.

I know I can use lambda A to put the message on another SQS, and then lambda B will listen to the new SQS. But I was wondering if there is a better way to run the lambdas one after another.

Thanks

you can make your worker lambda (ie lambda A) invoke lambda B. if you want to decouple it, make your lambda A publish to an SNS topic and have lambda B subscribe to it. — LostJon, Dec 10 '19 at 15:20

score 2 · Answer 1 · answered Dec 10 '19 at 17:35

You can invoke lambda B directly from lambda A with Lambda SDK.

You can invoke a function synchronously (and wait for the response), or asynchronously. To invoke a function asynchronously, set InvocationType to Event. For example:

import boto3

client = boto3.client('lambda')
response = client.invoke(
  FunctionName='lambda-b',
  InvocationType='Event',
  LogType='Tail',
  ClientContext='string',
  Payload=file,
  Qualifier='string'
)

Documentation for Python SDK (boto3) here

score 0 · Answer 2 · answered Dec 10 '19 at 16:09

0

You can use the Step Functions service. It will help you to coordinate different AWS services (Lambda, SQS, DynamoDb, ...) into a serverless workflow.

This is a nice Tutorial on how to use them: AWS Step Functions — A User’s Guide

AWS Step Functions Developer Guides is the offical docs that will show you all the things that you could do with Step Functions.

answered Dec 10 '19 at 16:09

alberto vielma

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only issue here is that you would need to have a lambda that was triggered by SQS to StartExecution for a step function. So, one more compute needs to be added to make this work, but I agree that ANY orchestration of lambda should be used w/ step functions. – LostJon Dec 10 '19 at 16:27
You could trigger your step function from whenever you want using the [Step Functions SDK](https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/StepFunctions.html). That could solve your issue depending in the serverless architecture you design. Let me know if works for you – alberto vielma Dec 10 '19 at 16:30
yea...to run that, you need some compute instance (being a lambda trigger). You cannot start a step function as a trigger from SQS – LostJon Dec 10 '19 at 16:33
Oh ok I get it better now. [Here](https://stackoverflow.com/questions/53422296/aws-sqs-trigger-step-functions), it was discussed the subject about triggering a step function using SQS. It seems it is not directly possible – alberto vielma Dec 10 '19 at 16:40

score 0 · Answer 3 · answered Dec 11 '19 at 12:08

You can invoke Lambda B directly from Lambda A.

here is a code for python

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

lambda_client = boto3_client('lambda', region_name='eu-west-1')

def lambda_handler(event, context):
    response = lambda_client.invoke(FunctionName="lambda_b",
                                           InvocationType='Event',
                                           Payload=json.dumps(event))
    print(response)

Please remember: you need to edit your role to allow a lambda invocation:

   {
        "Sid": "St125642120",
        "Effect": "Allow",
        "Action": [
            "lambda:InvokeFunction"
        ],
        "Resource": "*"
    }

Is there a way to trigger AWS lambda by another lambda and SQS?

3 Answers3