What's changed: Initial version (topic 2.13, subtopics 2.13.1–2.13.4)
7.1Approaches to High Availability
Learn the mindset behind systems that keep running: failure patterns (physical, logical, planned maintenance) and eliminating SPoF (single point of failure); the meaning and distinctions among MTBF, MTTR, availability, SLA, RPO, and RTO; and achieving resiliency through redundancy, clustering (Pacemaker, Corosync), load balancing, and geographic distribution.
Downtime costs revenue and trust directly. That is why operational design centers on high availability: not just staying up, but recovering fast when something breaks. This section walks through setting numeric targets, finding weak points, and closing them with redundant architecture.
7.1.1Failure patterns and eliminating SPoF
- Failure patterns fall into three groups: physical failures (hardware, power, network outages), logical failures (software bugs, misconfiguration, overload), and planned maintenance (scheduled downtime for patching or hardware swaps). Each calls for a different kind of countermeasure.
- SPoF (single point of failure) is a component whose failure stops the whole system: a lone load balancer, a single power feed, a single network path. The first step in HA design is drawing the architecture and hunting down every SPoF to eliminate with redundancy.
- Resiliency is the property of continuing to serve, or self-recovering, despite failures—not just redundancy, but automated failover and planned failback as well.
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