Key point
One idea
Scale up means use a bigger machine. Scale out means use more machines or more instances.
In your hackathon design, do not say “it scales” without naming the bottleneck. Say what gets bigger, what gets copied, and what can break.
When to scale up
Scale up first when one service is simple, traffic is low, and you want fewer moving parts. For a college hackathon demo, this is often enough for your backend or database.
Example: move from a small free database to a paid plan with more RAM, CPU, storage, or connections. The trade-off is cost and a hard limit. One large machine can still fail.