Learn in the textbookSystem Configurations for Availability and Reliability
DefinitionA cluster (クラスタ) links several computers over a network so they work together and appear to users as a single system.
ExplanationUsers can work without knowing which machine is handling their request. If one machine fails, the others take over its work, so the system as a whole keeps running. Adding machines also makes it easy to scale up.
AnalogyIt is like a shop where several clerks share one checkout line. When one goes on break the line keeps moving, and when more customers arrive the shop just adds clerks.
Memory hookA "cluster" can be a bunch of grapes. Many separate grapes look like one bunch, just as many machines look like one system.