Serverless vs Containers: AWS Lambda vs EC2

In the AWS ecosystem, there are two primary ways to run compute.

EC2 (Virtual Machines)

You rent a computer. It runs 24/7.

• Pros: Full control, persistent connections (WebSockets), consistent performance.
• Cons: You pay for idle time. You manage OS updates.

Lambda (Serverless)

You upload code. AWS runs it only when triggered (HTTP request, DB change).

• Pros: Zero idle cost. Auto-scaling from 0 to 1000s concurrently. No OS management.
• Cons: Cold Starts (latency on first request). 15-minute execution limit.

Use Case: Image Processing

Scenario: Users upload profile pictures. You need to resize them.

• EC2: Bad. You pay for the server even at 3 AM when no one uploads.
• Lambda: Perfect. Trigger Lambda on S3 upload. Resize. Done. Pay only for the 200ms of runtime.

Use Case: WebSocket Chat Server

Scenario: Real-time chat app.

• Lambda: Hard. Lambda dies after execution. It can't hold a WebSocket connection open.
• EC2: Perfect. Node.js server holding thousands of socket connections.

Choose the right tool for the traffic pattern.