CompTIA Exam Prep - ITF+, A+, Network+, Security+, CySA+

Redundancy comes in two shapes, and the choice between them determines cost, complexity and how long recovery takes. Active/active runs all nodes serving traffic simultaneously. Active/passive runs one while the other stands ready. Everything else in resilience design follows from that distinction. Active/passive One node handles everything; the standby monitors and takes over on failure. Failover may be automatic through a health check and a virtual address, or manual. The advantages are simplicity and predictability. There is one authoritative node, so no question of conflicting writes, and capacity planning is straightforward because a single node carries the full load by definition. The costs are real. The standby is paid for and idle, failover takes time — seconds to minutes, occasionally longer — and sessions in flight are usually lost. Worst of all, an untested standby frequently does not work: configuration drifts, a licence expires, a certificate lapses, and ...

Recovery Point Objective and Recovery Time Objective are the two numbers that turn "we need good backups" into an actual design. They are constantly confused, and the confusion is expensive, because they drive completely different spending. One buys backup frequency; the other buys standby capacity. The two definitions RPO is how much data you can afford to lose , measured backward from the moment of failure. An RPO of four hours means that after a disaster you accept losing up to four hours of work. It is a statement about data, and it sets how often you must capture a recoverable copy. RTO is how long you can afford to be down , measured forward from the moment of failure. An RTO of two hours means the service must be usable again within two hours. It is a statement about time, and it sets how fast your recovery mechanism must be. A timeline makes it concrete. The last backup completes at 10:00. The system fails at 14:00. Recovery finishes at 17:00. Data created betwee...