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In this article, you will see how a lambda function can be called from another lambda function.<\/p>\n
You will also see some use cases which illustrate the reasons for calling a lambda from another lambda.<\/p>\n
Use cases where you call one lambda from another lambda<\/b><\/strong><\/p>\n There are several occasions when you would like to do some tasks, by calling one lambda from another. Some of the use cases in which a lambda function can be used to call another lambda function are explained below:<\/p>\n Use Case 1: Using a Cron Lambda to call another lambda that does some job<\/p>\n There are use cases where you may want to set up one Lambda function as a cron task. This lambda function, in turn, could launch multiple instances of another lambda function that does some job.<\/p>\n Now, in this particular use case, we can also have one cron lambda function that is used to fire a non-lambda function, multiple times. However, in this case, the limitation is that the non-lambda function that performs the action cannot be consumed by other clients.<\/p>\n If, however, you use a cron lambda to call another lambda function to do the job, you could also allow other clients to call\/invoke the action lambda.<\/p>\n Use case 2 <\/b><\/strong>: Dividing large jobs into multiple lambdas<\/p>\n AWS Lambda service comes with a number of limitations which can be kept in mind while architecting good solutions.<\/p>\n For instance, there are some hard limitations for the runtime environment; the disk space is limited to 512 MB, memory can vary from 128 MB to 1536 MB, and the execution timeout for a function can be maximized in 5 minutes.<\/p>\n Thus, due to the size and runtime restrictions imposed on Lambda\u2019s, large jobs can be divided into multiple lambdas where one lambda function could be used to call another lambda function.<\/p>\n Steps that illustrate how a Lambda can be used to invoke another Lambda<\/b><\/strong><\/p>\n Let us now see how we can call one lambda from another lambda.<\/p>\n Step 1: Configure your role so that a lambda function can use it to call another lambda<\/b><\/strong><\/p>\n While\u00a0<\/b><\/strong>writing a Lambda function the invokes another lambda, you will need a Role that is configured with the required policies that allow the invocation of another lambda.<\/p>\n In this case, the role to which the policies are attached is lambda_basic_execution. <\/b><\/strong>You can, however, create your own roles and attach the required policies as shown below.<\/p>\n Login to the AWS Management console<\/b><\/strong>\u00a0and Choose IAM<\/b><\/strong>\u00a0option under Security, Identity & Compliance<\/b><\/strong>. This will take you to the \u201cWelcome to identity and Access Management<\/b><\/strong>\u201d page.<\/p>\n In this page Click on Roles<\/b><\/strong>. This will take you to a page which allows you to create a new role or search for an existing role.<\/p>\n If you want to create a new role and attach required policies to it, then click on Create role<\/b><\/strong>\u00a0button and continue further by attaching the required policies to it . In this case, however, we would be using the existing role i.e \u201c lambda_basic_execution\u201d.<\/b><\/strong><\/p>\n If you want to create a new role and attach required policies to it, then click on Create role<\/b><\/strong>\u00a0button and continue further by attaching the required policies to it . In this case, however, we would be using the existing role i.e \u201c lambda_basic_execution\u201d.<\/b><\/strong><\/p>\n \u00a0<\/b><\/strong><\/p>\n You need to ensure that \u00a0your role , lambda_basic_execution <\/b><\/strong>role\u00a0<\/b><\/strong>must have the\u00a0AWS Lambda Role <\/b><\/strong>policy attached to it as shown below. This policy allows the lambda function to invoke another lambda function.<\/p>\n If your lambda function does not use S3 you need not use AWS Lambda Execute<\/b><\/strong>\u00a0policy.<\/p>\n AWS Lambda Basic Execution Role<\/b><\/strong>\u00a0policy grants permissions including permissions for Amazon cloud watch actions that your lambda function needs.<\/p>\n Step 2: Create a Lambda function that calls another lambda<\/b><\/strong><\/p>\n In this step, you will see how a lambda function can be created that invokes another lambda function can be created.<\/p>\n In the Services menu, c<\/b><\/strong>lick on Lambda <\/b><\/strong>in the\u00a0Compute <\/b><\/strong>section. <\/b><\/strong>This\u00a0<\/b><\/strong>will take you to a page that allows you to create a lambda function and search for existing lambda functions.<\/p>\n In this page, click on Create function<\/b><\/strong>\u00a0button, to start creating a new lambda function.<\/p>\n This page allows you to provide a name for your Lambda function, choose your coding language, and choose a role that defines permissions for our function.<\/p>\n In this case, we have provided the name of the lambda function as call_lambda_lambda<\/b><\/strong>, used Python 3.6<\/b><\/strong>\u00a0as the coding language, and used an existing role i.e \u00a0lambda_basic_execution<\/b><\/strong>\u00a0which contained the required permissions to invoke another lambda.<\/p>\n Click on Create<\/b><\/strong>\u00a0function <\/b><\/strong>button to successfully create your lambda function, as shown below.<\/p>\n \u00a0<\/b><\/strong><\/p>\n In the Function Code<\/b><\/strong>\u00a0section, you can write code for your lambda function that invokes another lambda function.<\/p>\n Code :<\/b><\/strong><\/p>\n Code : call_lambda_lambda<\/b><\/strong> The following code shows the code written for\u00a0call_lambda_lambda<\/b><\/strong>\u00a0function that calls\u00a0api call\u00a0<\/b><\/strong>function.<\/b><\/strong><\/p>\n #import libraries import boto3 import json def lambda_handler(event, context): #Define object of lambda #Here service name is lambda and the region_name is the name of the region where the called function \u201capi call\u201d resides invoke Lam = boto3.client(\u201clambda\u201d,region_name=\u201dus-east-1\u2033) #Define a payload that needs to be passed with a message payload = {\u201cmessage\u201d: \u201cHi, You have been invoked\u201d} #Call the lambda function \u201capical\u201d by using the invoke method of the invokeLam object resp = invoke Lam.invoke(Function Name=\u201dapical\u201d, Invocation Type=\u201dEvent\u201d, Payload=json.dumps(payload)) #resp = invoke Lam.invoke(Function Name=\u201dapical\u201d, Invocation Type=\u201dRequest Response\u201d, Payload=json.dumps(payload)) print(resp) return \u201chello from lambda\u201d[\/source code]<\/p>\n In <\/i><\/em>\u201capicall\u201d<\/i><\/b><\/em><\/strong>\u00a0function, the event will contain the payload of the lambda function <\/i><\/em>\u201ccall_lambda_lambda\u201d.<\/i><\/b><\/em><\/strong><\/p>\n Step 3: Test your Lambda Function<\/b><\/strong><\/p>\n Once, you have, written the code for your lambda function, click on Save<\/b><\/strong>\u00a0button to save the code.<\/p>\n You can now test your lambda function by clicking on the Test<\/b><\/strong>\u00a0button.<\/p>\n This will prompt you to configure your test event. Enter a name for the test event and click on Create<\/b><\/strong> If your lambda function executes successfully without any errors, it will indicate the success message as shown below.<\/p>\n You can check the invidual log of call_lambda_lambda<\/b><\/strong>\u00a0function to check if it was successfully executed. You can also check the individual log of apicall <\/b><\/strong>to check if it was successfully invoked by call_lambda_lambda<\/b><\/strong>.<\/p>\n Log : call_lambda_lambda<\/b><\/strong><\/p>\n \u00a0<\/b><\/strong> Log : api call<\/b><\/strong> Keep watching this space for more articles on AWS services.<\/p>\n Reference url\u2019s:<\/b><\/strong><\/p>\n \u00a0<\/b><\/strong><\/p>\n https:\/\/lorenstewart.me\/2017\/10\/02\/serverless-framework-lambdas-invoking-lambdas\/<\/a><\/p>\n https:\/\/www.oreilly.com\/learning\/how-do-i-invoke-a-lambda-from-another-lambda-in-aws<\/a><\/p>\n https:\/\/www.youtube.com\/watch?v=5QwrseYLwNM&t=33s<\/a><\/p>\n https:\/\/www.youtube.com\/watch?v=5QwrseYLwNM<\/a><\/p>\n https:\/\/docs.aws.amazon.com\/lambda\/latest\/dg\/API_Invoke.html<\/a><\/p>\n https:\/\/serverfault.com\/questions\/703994\/awslambdaexecute-policy-definition<\/a><\/p>\n![\"\"](\"http:\/\/www.aqbsolutions.com\/wp-content\/uploads\/2018\/09\/image0011-1024x498-800x389.png\")
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\n<\/b><\/strong>The following code shows the code written for call_lambda_lambda<\/b><\/strong>\u00a0function that calls api call <\/b><\/strong>function.<\/b><\/strong><\/p>\n[source language=\"code\"]#import libraries import boto3 import json def lambda_handler(event, context): #Define object of lambda #Here service name is lambda and the region_name is the name of the region where the called function \"api call\" resides invoke Lam = boto3.client(\"lambda\",region_name=\"us-east-1\") #Define a payload that needs to be passed with a message payload = {\"message\": \"Hi, You have been invoked\"} #Call the lambda function \"apical\" by using the invoke method of the invokeLam object resp = invoke Lam.invoke(Function Name=\"apical\", Invocation Type=\"Event\", Payload=json.dumps(payload)) #resp = invoke Lam.invoke(Function Name=\"apical\", Invocation Type=\"Request Response\", Payload=json.dumps(payload)) print(resp) return \"hello from lambda\"[\/source code]\n\n \n\n<strong><em><b><i>In the above code, if you use the Event(asynchronous ) invocation option, the function will be invoked at least once in repose to an event, and the function must be idempotent to handle this.<\/i><\/b><\/em><\/strong>\n\n<strong><em><b><i>\u00a0<\/i><\/b><\/em><\/strong>\n\n<strong><em><b><i>If, however, you use the Request Response(synchronous) invocation option, the function will be invoked only once.<\/i><\/b><\/em><\/strong>\n\n<strong><em><b><i>\u00a0<\/i><\/b><\/em><\/strong>\n\n<strong><b>Code : apical<\/b><\/strong><\/pre>\n
\n<\/b><\/strong>to\u00a0<\/b><\/strong>create a new test event.<\/p>\n![\"\"](\"http:\/\/www.aqbsolutions.com\/wp-content\/uploads\/2018\/09\/image0171-1024x498-800x389.png\")
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\n<\/b><\/strong>Hope, by now, you know how and why one lambda function is invoked by another lambda function.<\/p>\n