Which of the following best describes a system that is always available, without the need for human intervention?

A system that is always available without the need for human intervention is best described as highly available. High availability refers to systems that are designed to operate continuously without failure for a long period of time, minimizing downtime and ensuring that services remain operational. This is typically achieved through redundancy and failover mechanisms, allowing the system to continue functioning even in the event of hardware or software failures.

In contrast, fault tolerance refers to the capacity of a system to continue operating despite the presence of failures. While fault tolerance is an important aspect of highly available systems, it does not necessarily imply that the system is always available or self-sustaining without human intervention.

Auto-scaling involves dynamically adjusting resources based on demand, which helps maintain performance during varying load conditions. However, it does not guarantee continuous availability on its own, as availability also depends on redundancy and infrastructure design.

Intermittently available indicates a system that does not maintain consistent uptime, which contradicts the concept of a system being always available. High availability centers on the idea of reliable, uninterrupted service, making it the most accurate description in this context.