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System & Operational Resilience
This episode of the ISACA Certified Information Systems Auditor (CISA) exam prep series covers system and operational resilience. It explains what it means to design systems that absorb and recover from disruption, introduces clustering and its two main configurations, and addresses the often-overlooked responsibility organisations carry for protecting their own telecommunication networks against outage.
What this episode covers
- System resilience defined — the ability to withstand hardware failures, network outages, cyberattacks, and software bugs while maintaining core functions.
- Clustering fundamentals — nodes, agents, and management software working together to eliminate single points of failure.
- Active-passive clustering — one active node with standby backups, simple failover without the application needing to be cluster-aware.
- Active-active clustering — all nodes running simultaneously with load balancing, requiring cluster-aware applications and low network latency.
- Combining approaches — active-active within a site for local resilience paired with active-passive between sites for disaster protection, spanning metro and geo-clusters.
- Telecom network resilience — why connectivity is the organisation’s own responsibility, and the six protection methods: redundancy, alternative routing, diverse routing, long-haul diversity, last-mile protection, voice recovery, and satellite.
Watch the full episode above for the worked examples and detailed explanations of each concept.
Frequently Asked Questions
What does system resilience mean in the context of IT operations?
System resilience is a system’s ability to withstand and adapt to disruption, including hardware failures, network outages, cyberattacks, and software bugs, while keeping its core functions running. It means absorbing the hit, recovering fast, and carrying on. The building blocks are redundant components, failover mechanisms, and solid backups, designed so that a single failed server does not take the whole service down.
How does clustering keep applications running and what is the difference between active-passive and active-active?
Clustering installs software on every server in a group, called nodes, with an agent on each node watching the application and removing single points of failure. In active-passive mode, the application runs on one active node while others wait as backups; if the active node fails, an agent restarts the application on a spare node without the application needing to know it is clustered. In active-active mode, the application runs on every node at once with agents balancing load and coordinating shared data access, so a failing node usually causes no user-visible downtime, but the application must be built to use the cluster and surviving nodes must rerun any unfinished transactions.
Why are telecommunication networks a special resilience concern?
Almost every business process now rides on telecommunication networks, so continuous connectivity must be a priority. Networks face natural disasters just like a data centre but also have unique threats including switching office failures, cable cuts, software glitches, hacking, and human error. Critically, keeping communications alive is the organisation’s own responsibility and not the carrier’s, meaning the carrier is not obliged to provide backup service, so the organisation must arrange to back up its own telecom facilities.
What methods protect telecommunication networks from outages?
Redundancy provides spare capacity and multiple paths between devices using dynamic routing and failover devices. Alternative routing sends traffic over a different medium such as copper, cellular, or microwave when the normal path fails. Diverse routing splits traffic through separate or duplicate cable facilities, though cables sharing one conduit can still both be cut by a single accident. Long-haul network diversity spreads long-distance traffic across multiple major carriers. Last-mile circuit protection guards the final stretch using a mix of terrestrial, microwave, and cable options, while voice recovery uses redundant cabling and voice-over-internet services, and satellite connectivity fills gaps where other options cannot reach.
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Reference: This article is based on concepts discussed in System & Operational Resilience.