Avoid This AWS Lambda Mistakes

AWS Lambda is a powerful tool for building serverless applications without managing servers. But if not used correctly, it can lead to performance issues, higher costs, or even security risks.

In this blog, we’ll go over 5 common mistakes developers make with AWS Lambda and how you can avoid them to build faster, cheaper, and more secure apps.

I. Using Lambda for Long-Running Tasks

The Mistake:

Trying to run jobs that take longer than 15 minutes in a Lambda function.

Why It’s a Problem:

Lambda has a maximum timeout of 15 minutes. Long-running tasks can time out and fail.

How to Avoid It:

Break the job into smaller steps using AWS Step Functions

Use AWS EC2 for heavy or long processes

II. Packaging Unnecessary Files and Libraries

The Mistake:

Bundling too many files, libraries, or dependencies into your Lambda deployment package.

Why It’s a Problem:

Large packages increase cold start times and make deployment slower and harder to debug.

How to Avoid It:

Include only what your code needs

Use Lambda Layers for shared dependencies

Use tools like Webpack to reduce file size

III. Ignoring Cold Starts

The Mistake:

Not optimizing for cold starts—delays that happen when Lambda is invoked after being idle.

Why It’s a Problem:

Cold starts can slow down performance, especially for user-facing applications.

How to Avoid It:

Allocate more memory (it improves CPU too)

Keep functions "warm" with CloudWatch Scheduled Events

Use Provisioned Concurrency for critical functions

IV. Over-Permissive IAM Roles

The Mistake:

Attaching broad permissions like AdministratorAccess to your Lambda functions.

Why It’s a Problem:

It increases the risk of security breaches and violates the principle of least privilege.

How to Avoid It:

Grant only the specific permissions needed

Use IAM Access Analyzer to review policies

Regularly audit IAM roles

V. Not Monitoring Costs and Performance

The Mistake:

Writing inefficient code or calling Lambda too frequently without cost awareness.

Why It’s a Problem:

You could end up with unexpectedly high AWS bills.

How to Avoid It:

Optimize your code for speed and efficiency

Monitor usage with Amazon CloudWatch

Set billing alerts in your AWS account

AWS Lambda is a powerful tool for serverless computing—but only when used correctly. By avoiding common mistakes, you can improve performance, reduce costs, and build a more secure and scalable cloud architecture.