A managed cluster server has a more complex structure. Instead of a website or an application relying on a single server, it relies on a group of servers that each serve a specific function.
The load balancers distribute the load across different application servers. The web servers house the actual application and the database layer stores the data.
We have standby web servers that we can run with any configuration in the event of peak loads. The entire structure is usually distributed across several data centres or availability zones.