Horizontal clustering: Running multiple nodes or instances of an application server on different hosts.
水平集群：在不同的主机上运行应用服务器的多个节点或实例。
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This horizontal isolation of the application provides the capability of the application to continue processing requests regardless of the running status of any one particular server.
这种应用程序的水平隔离提供应用程序继续处理请求而不管任何一个特殊的服务器的运行状态的能力。
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Once you have bottlenecked the vertical scaled server machine, you can consider to expand your application cluster to other machines, horizontal scale.