EC2 vs. Lambda vs. ECS: Which AWS Compute Service Should You Use?

Almost every AWS architecture question comes down to where your code runs. EC2, Lambda and ECS are the three answers you will meet most often.

EC2: full control of a virtual server

You pick the instance type, operating system and networking, and you patch and scale it yourself (or with Auto Scaling). Choose EC2 for long-running workloads, special software, or when you need control over the OS.

Lambda: run code without managing servers

You upload a function, AWS runs it on demand, and you pay for the time it runs. It suits event-driven tasks, APIs with spiky traffic and glue code. Watch the execution time limit and cold starts.

ECS: run containers

ECS runs Docker containers on EC2 or on Fargate, where AWS manages the servers. Choose it when your app is already containerised and you want steady, scalable services without running Kubernetes.

A simple rule of thumb

• Short, event-triggered code: Lambda.
• Containerised services that run all the time: ECS on Fargate.
• Anything needing OS-level control or special hardware: EC2.

In interviews, explain the trade-off (control versus operational effort versus cost), not just the definitions.