Handle more visitors
When an online shop gets busy, the team can make a server more powerful (scale up or vertical scaling) or add servers (scale out or horizontal scaling). Autoscaling adjusts capacity automatically as demand changes.
A load balancer sends each visitor’s request to an available server. It can use health checks to avoid servers that are not ready.
AWS offers Elastic Load Balancing (ELB), a service that does this.
More servers are not the whole answer
Adding servers will not help if the database cannot keep up. New servers also take time to start, so teams test busy periods and plan what the app should do if demand exceeds capacity.