DOP-C02 Resilient Cloud Solutions Practice Test 13 — 15 Questions

Question 1

A company has a production environment that uses Amazon Route 53 for DNS and an Application Load Balancer (ALB) to distribute traffic to EC2 instances. The company wants to implement a disaster recovery plan that automatically fails over to a secondary region in case the primary region becomes unavailable. Which configuration should be used?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Use Route 53 failover routing policy with primary and secondary records and health checks.. Route 53 failover routing policy with health checks on the ALB endpoint can automatically route traffic to a secondary endpoint when the primary is unhealthy. Option A is wrong because weighted routing distributes traffic based on weights, not failover. Option B is wrong because geolocation routing routes based on geographic location, not failover. Option D is wrong because latency routing routes based on latency, not automatic failover.

Answer

Use Route 53 weighted routing policy with equal weights for both regions.

Answer

Use Route 53 geolocation routing policy to route users based on their location.

Answer

Use Route 53 latency routing policy to route to the region with lowest latency.

Question 2

A company runs a critical microservice on Amazon ECS with AWS Fargate. The service must be highly available across multiple Availability Zones. The DevOps engineer configured the service with a desired count of 4 tasks spread across 2 Availability Zones. During a deployment, a new task fails to start due to a missing environment variable. The deployment fails, but the old tasks continue to run. What is the most likely cause of the deployment failure and how can the engineer ensure future deployments are resilient?

Accepted Answer

The deployment failed because the ECS service did not have the deployment circuit breaker enabled. Enable the circuit breaker with rollback.. The deployment failed because the new task could not start due to a missing environment variable, and the ECS service did not have the deployment circuit breaker enabled. Without the circuit breaker, ECS continues to attempt the deployment indefinitely or until a timeout, but it does not automatically roll back to the previous stable task set. Enabling the deployment circuit breaker with rollback ensures that if a specified number of tasks fail to start (e.g., due to health checks or runtime errors), ECS automatically rolls back to the last successful deployment, maintaining service availability.

Answer

The deployment failed because the ECS service was using the rolling update deployment controller. Change to blue/green deployment.

Answer

The deployment failed because the desired count was too low. Increase the desired count to 6.

Answer

The deployment failed because the health check grace period was too short. Increase the grace period.

Question 3

A company uses Amazon DynamoDB as the database for a mobile application. The application requires single-digit millisecond read and write latency and must be resilient to the failure of an entire AWS Region. Which DynamoDB feature should the company use?

Accepted Answer

DynamoDB global tables. DynamoDB global tables provide multi-Region, multi-active replication, ensuring the application can withstand an entire AWS Region failure while maintaining single-digit millisecond read and write latency in each Region. This is achieved through DynamoDB Streams and a last-writer-wins conflict resolution mechanism, making it the correct choice for cross-Region resilience.

Answer

DynamoDB point-in-time recovery (PITR)

Answer

DynamoDB Accelerator (DAX)

Answer

DynamoDB on-demand capacity mode

Question 4

A company is designing a highly available architecture for a web application that uses Amazon EC2 instances. The application must be resilient to the failure of a single instance and a single Availability Zone. Which TWO actions should the company take? (Choose TWO.)

Accepted Answer

Use an Auto Scaling group with a minimum of two instances spread across two Availability Zones.. An Auto Scaling group with a minimum of two instances spread across two Availability Zones ensures that if one instance or one entire AZ fails, the remaining instance(s) in the other AZ can continue serving traffic, and Auto Scaling will automatically launch a replacement instance in the healthy AZ to restore the desired count. Option B is correct because distributing EC2 instances across at least two Availability Zones is the fundamental requirement for AZ-level resilience, as it eliminates a single point of failure at the AZ boundary.

Answer

Place all EC2 instances in a single Availability Zone and use a Network Load Balancer.

Answer

Use a single Application Load Balancer in one Availability Zone.

Answer

Use a single large EC2 instance in one Availability Zone.

Question 5

A company is designing a disaster recovery plan for an Amazon S3 data lake. The data lake stores sensitive data that must be replicated to a secondary Region with an RPO of 15 minutes. Which THREE actions should the company take? (Choose THREE.)

Accepted Answer

Enable S3 Versioning on both the source and destination buckets.. Enabling S3 Versioning on both the source and destination buckets is a prerequisite for S3 Replication. Without versioning, replication cannot track object versions, which is essential for meeting the 15-minute RPO with consistency guarantees.

Answer

Configure S3 Event Notifications to trigger a Lambda function that copies objects to the secondary Region.

Answer

Enable S3 Transfer Acceleration on the source bucket.

Question 6

Refer to the exhibit. A DevOps engineer applies the IAM policy shown to an S3 bucket to enforce server-side encryption. However, users report that some uploads succeed without encryption. What is the most likely reason?

Accepted Answer

The policy only allows the action but does not deny actions that do not meet the condition.. The IAM policy only allows the s3:PutObject action when the encryption condition is met, but it does not include an explicit Deny statement to block uploads that do not satisfy the condition. In IAM, an Allow statement with a condition does not automatically deny requests that fail the condition; it simply does not apply the Allow. If there is another policy (e.g., a bucket policy or an identity-based policy) that grants s3:PutObject without the encryption condition, or if the default S3 behavior permits unencrypted uploads (since S3 does not require encryption by default), then unencrypted uploads can still succeed. To enforce encryption, you must add a Deny statement with a condition like `StringNotEquals` on `s3:x-amz-server-side-encryption` to explicitly reject requests that lack the required encryption header.

Answer

The policy uses StringEquals instead of StringNotEquals.

Answer

The resource ARN is incorrect; it should be the bucket ARN.

Answer

The action should be s3:PutEncryptedObject instead of s3:PutObject.

Question 7

Refer to the exhibit. A DevOps engineer runs the describe-target-health command and receives the output shown. The ALB target group has two instances. One instance is healthy, and the other is unhealthy with a 502 error. What is the most likely cause of the 502 error?

Accepted Answer

The application running on the instance is not responding correctly or has crashed.. A 502 Bad Gateway error from an ALB indicates that the target (EC2 instance) is not responding correctly or has closed the connection prematurely. This is commonly caused by the application or web server on the instance crashing or being unable to handle the request. Option A is incorrect because security group issues typically lead to connection timeouts (504) or refused connections, not 502. Option C is incorrect because a missing route to the internet gateway would cause network unreachability, resulting in a different error. Option D is incorrect because the health check path returning a 404 would cause the target to fail health checks, not return a 502 during actual traffic.

Answer

The security group for the instance does not allow inbound traffic on port 80 from the ALB.

Answer

The instance's route table does not have a route to the internet gateway.

Answer

The health check path is configured to return a 404 status code.

Question 8

A company is designing a disaster recovery strategy for a critical application that requires a Recovery Time Objective (RTO) of 15 minutes and a Recovery Point Objective (RPO) of 1 hour. The application runs on EC2 with data stored in Amazon RDS Multi-AZ. Which approach meets these requirements?

Accepted Answer

Use a pilot light strategy with RDS cross-Region read replicas and automated backups. A pilot light strategy with RDS cross-Region read replicas and automated backups meets the RTO of 15 minutes and RPO of 1 hour. The cross-Region read replica provides near-synchronous replication with an RPO typically under 5 seconds, and automated backups enable point-in-time recovery within the 1-hour RPO. The pilot light approach allows rapid promotion of the replica to a primary instance, achieving the 15-minute RTO by keeping minimal core services running in the DR Region.

Answer

Use backup and restore with daily snapshots to another Region

Answer

Use a warm standby with a scaled-down production environment in another Region

Answer

Use a Multi-AZ deployment in the same Region for DR

Question 9

A company runs a critical application on EC2 instances in an Auto Scaling group across three Availability Zones. The application uses an Amazon RDS Multi-AZ DB instance. During a recent incident, one Availability Zone experienced a complete failure. The application remained available, but performance degraded significantly. What is the most likely cause of the degradation?

Accepted Answer

The Auto Scaling group was configured to span only two Availability Zones, and the failed AZ contained a majority of the running instances. If the Auto Scaling group is configured to span only two Availability Zones, the failure of one AZ would result in a disproportionate loss of capacity. Since the failed AZ contained a majority of the running instances, the remaining instances in the surviving AZ would be overloaded, causing significant performance degradation. The application remained available because the surviving instances and the Multi-AZ RDS instance continued to operate, but the reduced compute capacity led to degraded performance.

Answer

The Route 53 health checks failed and directed traffic to another Region, increasing latency

Answer

The RDS DB instance failed over to a read replica in a different Region

Answer

The EBS volumes in the failed AZ were not available, causing data loss

Question 10

A company is designing a serverless application using AWS Lambda, Amazon API Gateway, and Amazon DynamoDB. The application must tolerate a Regional failure. Which design provides the most resilience?

Accepted Answer

Use DynamoDB global tables with Lambda functions deployed in multiple Regions and Route 53 multi-Region routing. DynamoDB global tables provide multi-Region, fully replicated tables with automatic conflict resolution, ensuring data availability during a Regional outage. Deploying Lambda functions in multiple Regions with Route 53 multi-Region routing (using health checks and latency-based or weighted routing) allows traffic to fail over to a healthy Region, making the entire serverless stack resilient to a Regional failure.

Answer

Use Lambda@Edge to run functions at AWS edge locations

Answer

Use DynamoDB auto-scaling and run Lambda in a single Region

Answer

Use DynamoDB Accelerator (DAX) to cache data across Regions

Question 11

A company runs a stateful web application on EC2 instances in an Auto Scaling group. The application uses an Application Load Balancer (ALB) and an Amazon ElastiCache Redis cluster. Users report that after a scaling event, they are logged out and lose session data. What is the most likely cause?

Accepted Answer

The ElastiCache cluster is not configured for Multi-AZ and a node failure caused all sessions to be lost. The scenario describes a stateful web application that relies on ElastiCache Redis for session storage. If the ElastiCache cluster is not configured for Multi-AZ, a node failure can cause all cached session data to be lost, logging users out. This is the most likely cause of session loss after a scaling event, as scaling events do not directly affect ElastiCache data persistence.

Answer

The ALB health check interval is too short, causing healthy instances to be marked unhealthy

Answer

The ElastiCache cluster is configured with in-transit encryption, causing session tokens to be invalidated

Answer

The Auto Scaling group is using a termination policy that terminates the oldest instance first, which holds active sessions

Question 12

A company uses Amazon Route 53 to route traffic to an Application Load Balancer. They want to improve availability by routing traffic to multiple ALBs in different AWS Regions. Which routing policy should they use?

Accepted Answer

Latency-based routing policy. Latency-based routing policy is correct because it directs traffic to the AWS Region that provides the lowest latency for the end user, improving availability and performance by distributing requests across multiple Application Load Balancers in different regions. This policy uses latency measurements between the user and each region to select the optimal endpoint, ensuring that if one region becomes unavailable, traffic is automatically routed to the next lowest-latency region.

Answer

Weighted routing policy

Answer

Geolocation routing policy

Answer

Simple routing policy

Question 13

A company runs a critical application on EC2 instances behind an Application Load Balancer. The application uses an Amazon RDS for PostgreSQL Multi-AZ DB instance. During a recent failover test, the application experienced a 5-minute downtime. The RDS failover completed within 30 seconds. What is the most likely cause of the prolonged downtime?

Accepted Answer

The application caches DNS resolutions, causing it to connect to the old writer endpoint. The most likely cause is that the application caches DNS resolutions, causing it to continue connecting to the old writer endpoint after failover. When an RDS Multi-AZ failover occurs, the DNS record for the writer endpoint is updated to point to the new primary instance, but the application's cached DNS entry still points to the old IP address. Since the old primary is now a standby and no longer accepts connections, the application experiences downtime until the DNS cache expires (typically 5–60 seconds) or the application refreshes the DNS resolution. The 5-minute downtime suggests the application uses a long DNS TTL or a custom caching layer that delays reconnection.

Answer

The RDS Multi-AZ failover took longer than expected due to a large transaction log

Answer

The Application Load Balancer health checks marked all instances as unhealthy during the failover

Answer

The application was using read replicas for writes, which failed during failover

Question 14

A company is designing a highly available architecture for a web application using AWS. Which TWO of the following design principles should be applied? (Select TWO.)

Accepted Answer

Deploy resources across multiple Availability Zones. Correct answers: C and D. Deploying resources across multiple Availability Zones (C) ensures high availability by tolerating an AZ failure. Using loosely coupled components like queues (D) improves resilience by decoupling components, preventing cascading failures and allowing independent scaling. Option A is wrong because running in a single AZ creates a single point of failure. Option B is wrong because storing session data on EC2 instances is not recommended for high availability; session data should be stored externally (e.g., ElastiCache or DynamoDB). Option E is wrong because tightly coupled components increase dependency and reduce fault tolerance.

Answer

Run all resources in a single Availability Zone to reduce complexity

Answer

Store session data on EC2 instances to improve performance

Answer

Use tightly coupled components to reduce latency

Question 15

A company is migrating a monolithic application to a microservices architecture on AWS. To improve resilience, which THREE design patterns should be implemented? (Select THREE.)

Accepted Answer

Retry with exponential backoff for transient failures. Implementing retry with exponential backoff allows services to handle transient failures (e.g., network timeouts, throttling) by automatically retrying operations after increasing delays, reducing load on recovering systems. This pattern is essential for microservices on AWS, where services like DynamoDB or Lambda may throttle requests, and exponential backoff (e.g., using jitter as per AWS SDK defaults) prevents cascading failures.

Answer

Synchronous communication between services to ensure consistency

Answer

Single shared database to maintain data consistency