cold-start – DevWharf

Serverless computing lets you run code without managing servers. AWS Lambda and Azure Functions are the two dominant platforms — same core concept (event-driven, pay-per-execution) but different developer experiences, ecosystems, and operational characteristics. Here’s a grounded comparison.

How Serverless Works

Both execute functions in response to events: HTTP requests, queue messages, file uploads, database changes, or scheduled timers. You write a handler, deploy it, and the platform manages scaling, availability, and infrastructure. You pay only for compute time used — measured in milliseconds. When traffic spikes to 10,000 concurrent requests, instances provision automatically. When idle, you pay nothing.

Handler Patterns

// AWS Lambda — Node.js
exports.handler = async (event, context) => {
    const name = event.queryStringParameters?.name || "World";
    return {
        statusCode: 200,
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ message: `Hello ${name} from Lambda!` })
    };
};

// Azure Functions — Node.js v4 model
const { app } = require('@azure/functions');
app.http('hello', {
    methods: ['GET'],
    handler: async (request, context) => {
        const name = request.query.get('name') || 'World';
        return { status: 200, jsonBody: { message: `Hello ${name} from Azure!` } };
    }
});

Ecosystem Integration

Lambda integrates tightly with AWS: API Gateway, DynamoDB Streams, S3, SQS, SNS, EventBridge, Step Functions, Kinesis. Azure Functions integrates with Cosmos DB, Blob Storage, Service Bus, Event Grid, plus Microsoft 365 and Power Platform. Choose based on your existing cloud ecosystem.

Cold Starts & Performance

Cold starts (100ms-2s latency for new instances) affect both. Lambda offers Provisioned Concurrency and SnapStart (Java). Azure offers a Premium Plan with pre-warmed instances. Both have improved dramatically — cold starts are far less impactful than three years ago.

Pricing

Both offer 1 million free requests and 400,000 GB-seconds/month. Beyond free tier: ~$0.20/million requests and ~$0.0000167/GB-second. Lambda’s ARM64 (Graviton) provides 34% better price-performance for many workloads. Cost differences come from architecture choices, not per-request pricing.

Developer Experience

Lambda: SAM, CDK, Serverless Framework; sam local invoke for testing. Azure Functions: Deep VS Code integration, Core Tools CLI with live-reload, plus Durable Functions for stateful workflows (function chaining, fan-out/fan-in, human interaction patterns).

The Verdict

Already on AWS? Lambda. Azure/Microsoft shop? Azure Functions. Greenfield? Choose based on which cloud’s broader services fit your needs — the serverless compute layer is comparable. Both are production-ready with massive communities.

Further reading: AWS Lambda Docs | Azure Functions Docs

Tag: cold-start

AWS Lambda vs Azure Functions: A Practical Serverless Comparison