Redundancy

SDL Tridion Sites supports network load balancing and server clustering in order to provide a redundant, fault-tolerant environment.

Content management environment
The goal of SDL is high availability, that is, ensuring the system is available for as close to 100% as possible. Failover means that should one system fail, another system will take over without interruption. Failover is a component of a high-availability solution. For Content Manager high availability, you need at least two management servers and the database server on a cluster. Content Manager automatically supports failover when installed in a network load-balanced cluster.
Content Delivery environment
The Content Delivery feature fully supports failover. To support high availability and failover you need at least two machines in a load-balanced configuration. If you deploy other third-party or custom applications in the delivery environment, it is the responsibility of these applications to provide their own failover facilities.

Robust, well-scaled environments need to include the right people to ensure proper maintenance.