What does high availability mean in mission-critical systems?

What does high availability mean in mission-critical systems?

• A. A design goal to ensure a service remains accessible with minimal planned and unplanned downtime, typically via redundancy and failover.
• B. A model where all components are kept offline for maintenance.
• C. A system that guarantees zero downtime.
• D. A single active component with no redundancy.

Answer: (A)

High availability means keeping a service reachable and usable with minimal downtime, even if parts of the system fail or need maintenance. The goal is not to promise perfect no downtime, but to minimize interruptions by using redundancy and quick recovery. Redundancy means having duplicate components, links, or data paths so that if one part fails, another can take over. Fast failover and automated health checks ensure traffic or requests are redirected to healthy components without long pauses. In practice, you might see multiple servers, mirrored databases, redundant networks, and load balancers that continuously monitor health and switch over as needed. This approach contrasts with designs that rely on a single component or that require taking the entire system offline for maintenance.

High availability means keeping a service reachable and usable with minimal downtime, even if parts of the system fail or need maintenance. The goal is not to promise perfect no downtime, but to minimize interruptions by using redundancy and quick recovery. Redundancy means having duplicate components, links, or data paths so that if one part fails, another can take over. Fast failover and automated health checks ensure traffic or requests are redirected to healthy components without long pauses. In practice, you might see multiple servers, mirrored databases, redundant networks, and load balancers that continuously monitor health and switch over as needed. This approach contrasts with designs that rely on a single component or that require taking the entire system offline for maintenance.