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CLF-006
Which of the following is the most appropriate design for achieving high availability?
Choices
Explanation and answer
Read the explanation and correct answer (spoiler — try answering first)
Correct answer: D. Place resources across multiple Availability Zones.
Explanation
To improve high availability, designs that use multiple AZs and redundancy to reduce single points of failure are important.
Per-choice explanations
A. Take no backups at all.
Incorrect. Backups are important for recovery.
B. Stop all monitoring services.
Incorrect. Stopping monitoring delays failure detection.
C. Store all data on only one EC2 instance.
Incorrect. Consolidating onto a single instance makes the system more likely to stop during a failure.
D. Place resources across multiple Availability Zones.
Correct. Distributing across multiple AZs makes the system more resilient to failures.
Practical Use
High Availability (HA) refers to the property of a system that can continue to provide service even when unexpected failures occur. The basic patterns for achieving high availability on AWS are distributing resources across multiple Availability Zones, distributing traffic via a load balancer, redundant databases that include standby systems, and the combination of regular backups and monitoring. The standard configuration is to span the web tier across two or more AZs using an ALB with an Auto Scaling Group, and to make the data tier redundant in writers and readers using RDS Multi-AZ or an Aurora cluster configuration. Related concepts to high availability are fault tolerance, disaster recovery, and backup and restore, each of which has different goals and means. High availability focuses on not stopping service even when a single component fails, while disaster recovery focuses on switching to another Region when a Region-scale failure occurs and is designed around metrics such as RTO (Recovery Time Objective) and RPO (Recovery Point Objective). The higher you make availability, the more complex the configuration becomes and the higher the cost. The practical foundation is to clarify the acceptable downtime as a business requirement before designing. On CLF-C02, distribution across multiple AZs frequently appears as the correct answer for high-availability designs. Distractors include extreme choices that directly impair availability, such as consolidating everything onto a single EC2 instance, not taking backups, or stopping monitoring. In higher-level exams such as SAA-C03, more advanced design decisions are asked, such as the proper use of Multi-AZ and Read Replicas (the former for availability, the latter for read performance), or the difference between active/passive and active/active configurations.