Design resilient architectures

A web application requires a relational database that can withstand the failure of an entire Availability Zone with automatic failover. Which configuration meets this requirement?

• A Amazon RDS with a read replica in the same AZ
• B Amazon RDS Multi-AZ deployment ✓
• C A single-AZ RDS instance with automated backups
• D Amazon RDS with a read replica in another Region

Answer: RDS Multi-AZ maintains a synchronous standby replica in a different AZ and automatically fails over if the primary fails, providing high availability. Read replicas are for scaling reads, not automatic failover.

A solutions architect needs to decouple a web tier from a backend processing tier so that messages are not lost if the backend is temporarily unavailable. Which service is MOST appropriate?

• A Amazon SNS
• B Amazon SQS ✓
• C AWS Step Functions
• D Amazon Kinesis Data Streams

Answer: Amazon SQS is a managed message queue that buffers messages durably, allowing the backend to process them when available and preventing message loss during outages.

An architect wants to ensure an Auto Scaling group always maintains at least two healthy instances across multiple Availability Zones. Which setting achieves this?

• A Set the maximum capacity to two
• B Set the desired and minimum capacity to two and span multiple AZs ✓
• C Use a single AZ with a launch template
• D Disable health checks to avoid replacements

Answer: Setting minimum capacity to two and configuring the group across multiple AZs ensures the Auto Scaling group maintains at least two healthy instances spread for resilience.

An application must broadcast a single message to multiple subscribers, including Lambda functions and SQS queues, simultaneously. Which service should be used?

• A Amazon SQS
• B Amazon SNS ✓
• C Amazon MQ
• D AWS Step Functions

Answer: Amazon SNS implements publish/subscribe messaging, delivering a single published message to multiple subscribers such as Lambda, SQS, and HTTP endpoints in a fan-out pattern.

A company needs to ensure that deleted or overwritten objects in an S3 bucket can be recovered. Which feature should be enabled?

• A S3 Transfer Acceleration
• B S3 Versioning ✓
• C S3 Lifecycle policies
• D S3 Object Lock in governance mode only

Answer: S3 Versioning keeps multiple versions of an object, allowing recovery from accidental deletions or overwrites by restoring a previous version.

A web application must remain available even if an entire AWS Region becomes unavailable. Which approach BEST achieves this?

• A Deploy across multiple AZs in one Region
• B Deploy a multi-Region active-passive architecture with Route 53 failover ✓
• C Use a single large EC2 instance
• D Enable RDS Multi-AZ only

Answer: A multi-Region architecture with Route 53 DNS failover can redirect traffic to a healthy Region if the primary Region fails, providing resilience against Region-wide outages.