Architecting on AWS Certification High Availability & Fault Tolerance Flashcards
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Which AWS service enables you to create a pilot-light disaster recovery strategy by maintaining a minimal version of your environment running in a secondary Region?
Answer: AWS Elastic Disaster Recovery
AWS Elastic Disaster Recovery (DRS) continuously replicates source servers to a staging area and can quickly scale up a full environment in a secondary Region during a disaster.
Which CloudWatch metric would an architect monitor to detect that an Application Load Balancer has no healthy targets available?
Answer: HealthyHostCount
The HealthyHostCount metric reports the number of targets the load balancer considers healthy; a value of 0 means no healthy targets are available.
An application must maintain session state even if the EC2 instance serving a user is replaced. Which solution achieves this with the least application change?
Answer: Store sessions in Amazon ElastiCache
Storing session data in ElastiCache externalizes state from EC2 instances so any instance can serve returning users regardless of which instance previously handled them.
What RTO (Recovery Time Objective) characteristic distinguishes a warm standby DR strategy from a pilot light strategy?
Answer: Warm standby has a shorter RTO because a scaled-down but fully functional environment is already running
In warm standby, a fully functional but scaled-down replica is always running, so failover only requires scaling up rather than starting services from scratch.
Which AWS Global Infrastructure feature ensures that an EC2 instance placed in a specific Availability Zone is physically isolated from instances in other AZs within the same Region?
Answer: AZ physical separation
Each Availability Zone is a physically distinct location with independent power, cooling, and networking, providing fault isolation from other AZs in the Region.
An architect designs a multi-AZ architecture for an RDS database. Which statement about automated failover is correct?
Answer: Failover updates the DB endpoint DNS record to point to the standby
During Multi-AZ failover, Amazon RDS automatically updates the DNS record of the DB endpoint to resolve to the standby instance, allowing the application to reconnect without a code change.