Think capacity, then adaptation
A system is scalable if it can grow to serve a larger workload. An elastic system adjusts its resources to match changing demand. Managed services can do much of this work behind the scenes.
Amazon S3 manages storage capacity
S3 automatically scales to higher request rates, although scaling is gradual. A static S3 website does not need an EC2 Auto Scaling group. A CDN such as CloudFront can cache files closer to visitors and reduce requests to the origin.
Cloudflare Pages distributes delivery
Pages publishes static assets to Cloudflare's global network. You do not provision a fleet of web servers to serve them. Static asset requests are free and unlimited under the documented Pages pricing; Functions have separate quotas and billing.
Measure what visitors experience
Request counts show activity. Latency shows how long delivery takes. Error counts reveal failed requests. A few manual visits demonstrate that a site works, but do not establish its maximum capacity or prove elasticity.