Serverless on AWS: When It Makes Sense and When It Doesn't

"We cut our AWS bill by 90% going serverless!"

"Serverless was a nightmare — we're moving everything back to EC2."

If you've spent any time in tech forums lately, you've probably seen both of these takes. And here's the thing: they're both right. Serverless on AWS can be either a game-changer or a costly mistake, depending entirely on how you use it.

What "Serverless" Actually Means (Spoiler: There Are Still Servers)

Let's clear this up right away — "serverless" doesn't mean there are no servers.

It means you don't manage them.

In the AWS world, serverless typically means a cocktail of services like Lambda (for compute), API Gateway (for HTTP endpoints), DynamoDB (for data), and S3 (for storage). You write code, AWS runs it, and you only pay when it executes.

Think of it like taking an Uber instead of owning a car. You don't worry about maintenance, parking, or insurance — you just pay for the ride when you need it.

The Serverless Promise: Why Everyone's Excited

1. Pay-Per-Use Economics

Traditional EC2 instance sitting idle at 2 AM? You're still paying for it.

Lambda function that hasn't been called in three days? Zero cost.

For applications with variable or unpredictable traffic, this model can slash costs dramatically. One e-commerce client we worked with saw their overnight infrastructure costs drop from $800/month to under $50 just by moving their order processing to Lambda.

2. Infinite* Scale (*Terms and Conditions Apply)

Need to handle 10 requests per second? Lambda's got you.

Suddenly need 10,000? Lambda scales automatically.

No more panicked 3 AM calls about servers melting under Black Friday traffic. AWS handles the scaling, you handle the celebrating.

3. Less Ops, More Development

Remember the last time you had to patch a server? Update an OS? Configure a load balancer?

With serverless, those tasks disappear. Your team can focus on building features instead of maintaining infrastructure.

The Dark Side: When Serverless Becomes "Serverless"

Cold Starts: The Achilles' Heel

Here's what AWS doesn't put in the marketing materials: the first time your Lambda function runs after being idle, it's slow. Really slow.

We're talking anywhere from 100ms to several seconds of additional latency. For a real-time trading platform or a gaming backend? That's unacceptable.

Vendor Lock-In Is Real

Your Lambda functions aren't just "functions" — they're tightly integrated with API Gateway, DynamoDB, SQS, and a dozen other AWS services.

Want to move to Google Cloud next year? Hope you enjoy rewriting everything.

The 15-Minute Wall

Lambda functions have a hard limit: 15 minutes of execution time. Period.

Processing a massive video file? Running a complex machine learning model? Generating detailed reports? You'll hit that wall fast, and there's no way around it.

The Million-Dollar Question: When Should You Go Serverless?

Perfect Fit: Event-Driven Workloads

Image processing pipeline? Perfect. Each upload triggers a Lambda, processes the image, and shuts down.

Webhook handlers? Ideal. Sporadic traffic, quick processing, minimal cost.

Scheduled tasks? Excellent. Run your daily reports without maintaining a server 24/7.

Also Great For:

• APIs with variable traffic — Let AWS handle the scaling headaches
• Microservices — Each function does one thing well
• Proof of concepts — Get to market fast, optimize later
• Mobile/IoT backends — Handle millions of sporadic connections efficiently

Run Away When You Have:

Consistent high traffic — If you're processing 1000+ requests per second constantly, EC2 with reserved instances will be cheaper.

Long-running processes — That 15-minute limit isn't negotiable.

Complex local state — Lambda functions are stateless. Need to maintain connections or cache data in memory? Look elsewhere.

Ultra-low latency requirements — Cold starts will ruin your day.

The Cost Reality Check

Let's talk money — because that's what your CFO cares about.

When Serverless Saves Money:

• Traffic varies by 10x or more daily
• You process less than 1 million requests/month
• Your functions run for seconds, not minutes
• You're currently over-provisioned on EC2

When It Gets Expensive:

• Constant high traffic (>1000 req/sec sustained)
• Functions running for minutes at a time
• Heavy data transfer between services
• Extensive use of API Gateway (it's pricier than you think)

Real-World Architecture: Hybrid Is Usually the Answer

Here's what successful serverless architectures actually look like:

Core application: Traditional servers (ECS, EKS, or EC2) Variable workloads: Lambda functions Static assets: S3 + CloudFront Background jobs: Mix of Lambda (short) and ECS tasks (long)

One fintech startup we advised uses Lambda for webhook processing, document generation, and notification sending — but keeps their core transaction engine on ECS. Best of both worlds.

Making the Decision: Your Serverless Checklist

Before going all-in on serverless, ask yourself:

1. Is your workload event-driven? ✅ Good fit
2. Do you have predictable, high traffic? ❌ Consider traditional
3. Are your processes under 15 minutes? ✅ Good fit
4. Can you tolerate occasional cold starts? ✅ Good fit
5. Is your team small or ops-constrained? ✅ Good fit
6. Do you need complex local state? ❌ Consider traditional

The Bottom Line

Serverless isn't about following trends — it's about matching architecture to your actual needs.

For event-driven, variable workloads with simple processing requirements, serverless can dramatically reduce both costs and operational overhead. But trying to force-fit it where it doesn't belong will leave you with a complex, expensive mess.

The best architects we know use serverless as a powerful tool in their toolkit — not as a religion. They deploy Lambda where it shines and stick with traditional architecture where it makes sense.

Because at the end of the day, the best architecture is the one that lets you ship features quickly, scale efficiently, and sleep soundly at night. Whether that includes Lambda or not.

Entvas Editorial Team

Helping businesses make informed decisions