AWS Lambda Function Code Decomposed

In this article, we are going to learn Lambda Function Code and Best Practices Related to the Lambda Lifecycle.

By the end of the article, we will learn AWS Lambda Function Code parts and Key Concepts of AWS Lambda functions.

I have just published a new course — AWS Lambda & Serverless — Developer Guide with Hands-on Labs.

AWS Lambda Function Code

AWS Lambda runs instances of your function to process events. We can invoke your function directly using the Lambda API, or you can configure an AWS service or resource to invoke your function. You can find the image at below which is a Lambda function with Node.js version.

As you can see that we have lambda function name that we export in handler method. And we have defined function which has event, context and callback parameters. With this parameters we develop our actual business function and after that perform some callback operations that can be return a response or not respond for async invocations.

So AWS Lambda function has code to process the events that you pass into the function or that other AWS services send to the function with event json object. The event object contains all the information about the event that triggered this Lambda. For example if lambda invokes from api gateway, then an HTTP request will be the information of event. The context object contains info about the runtime our Lambda function is executing in.

After we do all the work inside our Lambda function, we simply call the callback function with the results and AWS will respond to the HTTP request with it.

There are also several key concepts when writing lambda function code like event, trigger, execution environment, Layer an so on.. when writing our function code.

AWS Lambda Function Key Concepts

In this part we will learn AWS Lambda Function Key Concepts.


We can select the runtime as part of configuring the function, and Lambda loads that runtime when initializing the environment.

Handler Method

Our function runs starting at the handler method. It is a best practice to separate the Lambda Handler from your business logic.


A function is a resource that you can invoke to run your code in Lambda and function has code to process the events that you pass into the function or that other AWS services send to the function.


A trigger is a resource or configuration that invokes a Lambda function. Triggers include AWS services that you can configure to invoke a function and event source mappings.


An event is a JSON-formatted document that contains data for a Lambda function to process.

Execution environment

An execution environment provides a secure and isolated runtime environment for your Lambda function.


A Lambda layer is a .zip file archive that can contain additional code or other content.


Concurrency is the number of requests that your function is serving at any given time.


A destination is an AWS resource where Lambda can send events from an asynchronous invocation.

Best Practices of Lambda Function Code

Now we can exposed some of best practices that we can follow when developing AWS Lambda functions.

▪ Take advantage of environment reuse, and check that background processes have completed.

▪ Manage database connection pooling with a database proxy. Persist state data externally.

▪ Configure Function with Resource-based policy. Resource based policy grants permissions to invoke your lambda function. Execution role defines a function’s permission to interact with resources.

▪ Use Environment variables to store secrets securely and adjust your function’s behavior without updating code.

Step by Step Design AWS Architectures w/ Course

I have just published a new course — AWS Lambda & Serverless — Developer Guide with Hands-on Labs.

In this course, we will learn almost all the AWS Serverless Services with all aspects. We are going to build serverless applications with using AWS Lambda, Amazon API Gateway, Amazon DynamoDB, Amazon Cognito, Amazon S3, Amazon SNS, Amazon SQS, Amazon EventBridge, AWS Step Functions, DynamoDB and Kinesis Streams. This course will be 100% hands-on, and you will be developing a real-world application with hands-on labs together and step by step.

Source Code

Get the Source Code from Serverless Microservices GitHub — Clone or fork this repository, if you like don’t forget the star. If you find or ask anything you can directly open issue on repository.



AWS Serverless with AWS Lambda, API Gateway, Amazon DynamoDB, Cognito, S3, SNS, SQS, EventBridge, Step Functions, DynamoDB and Kinesis Streams, CloudFormation, SAM, CDK. We will develop Lambda-based event-driven application integrate to all AWS Serverless Services.

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Mehmet Ozkaya

Software/Solutions Architect, Udemy Instructor, Working on Cloud-Native and Serverless Event-driven Microservices Architectures