Understanding Serverless Computing with AWS Lambda: A Practical Guide for Modern Developers

📘 Chapter 3: Writing and Deploying Lambda Functions

🔍 Overview

At the core of AWS Lambda is the function itself — a small unit of code designed to run on-demand. This chapter focuses on writing Lambda functions in supported languages, understanding the function handler structure, using environment variables, managing dependencies, and deploying using multiple methods such as the console, CLI, container images, and popular frameworks like SAM and Serverless Framework.

✏️ 1. Lambda Function Basics

✅ Components of a Lambda Function

🧠 2. Writing Your First Function

Let’s look at basic Lambda function examples in different languages.

✅ Node.js Example

javascript

exports.handler = async (event) => {

    console.log("Event received:", JSON.stringify(event));

    return {

        statusCode: 200,

        body: JSON.stringify({ message: "Hello from Node.js Lambda!" })

    };

};

✅ Python Example

python

def lambda_handler(event, context):

    print("Event:", event)

    return {

        "statusCode": 200,

        "body": "Hello from Python Lambda!"

    }

✅ Java Example

java

public class HelloLambda implements RequestHandler<Map<String,String>, String> {

    public String handleRequest(Map<String,String> event, Context context) {

        return "Hello from Java Lambda!";

    }

}

🧪 3. Using Environment Variables

Environment variables are key-value pairs that let you configure functions without hardcoding values.

✅ Set via Console or CLI

bash

aws lambda update-function-configuration \

  --function-name MyFunction \

  --environment "Variables={DB_HOST=db.example.com,DB_PORT=3306}"

✅ Access in Code

• Node.js: process.env.DB_HOST
• Python: os.environ['DB_HOST']

📦 4. Managing Dependencies

If your function uses external libraries, package them along with your function code.

✅ Node.js

bash

npm init -y

npm install axios

zip -r function.zip index.js node_modules/

✅ Python

bash

pip install requests -t .

zip -r function.zip lambda_function.py requests/

You can also use Lambda Layers to reuse packages across functions.

🚀 5. Deployment Methods

Lambda supports multiple deployment approaches depending on your development workflow.

✅ A. Console Deployment (for quick tests)

• Ideal for simple logic
• Not recommended for large functions or version control

✅ B. ZIP File Deployment (CLI)

bash

zip function.zip index.js

aws lambda update-function-code \

  --function-name MyFunction \

  --zip-file fileb://function.zip

✅ C. Container Image Deployment

1. Create Dockerfile

Dockerfile

FROM public.ecr.aws/lambda/nodejs:18

COPY app.js package.json ./

RUN npm install

CMD ["app.handler"]

2. Build & Push Image

bash

docker build -t my-lambda-image .

aws ecr create-repository --repository-name my-lambda-repo

docker tag my-lambda-image:latest <ECR_URI>

docker push <ECR_URI>

3. Deploy Function

bash

aws lambda create-function \

  --function-name MyContainerLambda \

  --package-type Image \

  --code ImageUri=<ECR_URI> \

  --role arn:aws:iam::123456789012:role/LambdaExecutionRole

✅ D. AWS SAM (Serverless Application Model)

Template Example (template.yaml):

yaml

AWSTemplateFormatVersion: '2010-09-09'

Transform: AWS::Serverless-2016-10-31

Resources:

  HelloWorldFunction:

    Type: AWS::Serverless::Function

    Properties:

      Handler: index.handler

      Runtime: nodejs18.x

      CodeUri: .

      MemorySize: 128

      Timeout: 5

Deploy:

bash

sam build

sam deploy --guided

✅ E. Serverless Framework

serverless.yml:

yaml

service: hello-lambda

provider:

  name: aws

  runtime: nodejs18.x

functions:

  hello:

    handler: handler.hello

Deploy:

bash

sls deploy

🔄 6. Versioning and Aliases

• Lambda supports function versions for immutability
• Aliases act as pointers to versions (e.g., dev, prod)

bash

aws lambda publish-version --function-name MyFunction

aws lambda create-alias --function-name MyFunction \

  --name prod --function-version 2

🔍 7. Debugging and Logging

Use CloudWatch Logs to view logs from your function.

✅ Log Access via CLI

bash

aws logs filter-log-events \

  --log-group-name /aws/lambda/MyFunction

Log inside your handler:

• Node.js: console.log()
• Python: print()
• Java: System.out.println()

🧠 8. Best Practices

• Keep functions small and focused
• Use environment variables for secrets/configs
• Use layers for shared dependencies
• Implement timeouts and error handling
• Keep your code stateless
• Log input/output for debugging
• Use SAM or Serverless Framework for scalable deployments

📋 Summary Table – Writing and Deploying Lambda