Explain what is high availability, high reliability and scalability

In accordance with the definition of the relevant international organizations, the degree to which a device is in a working or usable state at any random moment when it is needed and begins to perform a task. Usually expressed in terms of availability (A0), which combines reliability, maintainability, testability, security and other product design features into a parameter that users care about using. The probabilistic measure of availability is called "availability". Inherent availability AI = TBF / (TBF + MCT) where: TBF is the average time between failures (hours), MCT is the average repair time (hours). Usage Availability A0=Accumulated Working Time/(Accumulated Working Time+Accumulated Non-Working Time) Accumulated Non-Working Time includes Accumulated Direct Maintenance Time and Accumulated Maintenance Guarantee Delay Time MLDT. so: A0=MTBF/(MTBF+MTTR+MLDT) Definition of Reliability: The ability of a product to fulfill a specified function under specified conditions and within a specified period of time. The probability measure of reliability is called reliability. High reliability means that the device has a high level of reliability, e.g., an average trouble-free operating time of more than 10,000 hours is higher than 1,000 hours. Scalability refers to equipment designed to become a modular structure, and has a high level of reliability, can be combined with newly designed functional modules into a new type of equipment, with good system functions and high reliability and availability levels.