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CLF-039
Which of the following best describes the approach to achieving high availability in the cloud?
Choices
Explanation and answer
Read the explanation and correct answer (spoiler — try answering first)
Correct answer: A. Use multiple Availability Zones to reduce the impact of failures
Explanation
To achieve high availability, it is important to reduce single points of failure and to distribute resources across multiple Availability Zones.
Per-choice explanations
A. Use multiple Availability Zones to reduce the impact of failures
Correct. Using multiple AZs limits the impact of a single AZ failure.
B. Do not take any backups
Incorrect. A design without backups is fragile when recovering from failures.
C. Concentrate all processing on a single physical server
Incorrect. Concentrating on a single server becomes a single point of failure.
D. Restrict all communication to HTTP only
Incorrect. Restricting all communication to HTTP is not an approach for high availability.
Practical Use
High availability is a design philosophy aimed at minimizing the time that an overall system is unavailable. In AWS, each Region consists of multiple Availability Zones (AZs). An AZ is a set of physically independent data centers with separated power, cooling, and networking, so a failure in one AZ does not propagate to other AZs. By distributing resources across multiple AZs, you can avoid a complete outage caused by a failure in a single AZ. On the exam, the typical question asks which approach achieves high availability, with multiple AZs as the correct answer. Distractors include concentrating all processing on a single physical server, not taking any backups, and restricting all communication to HTTP only. These contradict the definition of high availability. Extreme concentration, abandoning backups, and protocol restriction all increase single points of failure and are incorrect from an availability standpoint. In practice, a multi-AZ configuration is implemented by placing EC2 instances behind an Application Load Balancer or Network Load Balancer across multiple AZs, configuring an Amazon RDS Multi-AZ deployment so that the standby is in a different AZ, or choosing services such as Amazon S3 that store data redundantly across multiple AZs by default. CLF-C02 repeatedly tests the difference among Region, AZ, and edge location, and the distinction between Multi-AZ for AZ-level failures and multi-Region for large-scale disasters.