DOP-C02 Resilient Cloud Solutions Practice Test 17 — 15 Questions

Question 1

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?

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

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 2

A company runs a stateless web application on EC2 instances behind an Application Load Balancer. To improve resilience, which configuration should be used for the EC2 instances?

Accepted Answer

Use multiple EC2 instances across two or more Availability Zones. D is correct because deploying multiple EC2 instances across two or more Availability Zones (AZs) ensures high availability and fault tolerance. If one AZ fails, the Application Load Balancer (ALB) automatically routes traffic to healthy instances in other AZs, maintaining service continuity. This aligns with the AWS Well-Architected Framework's resilience best practices for stateless applications.

Answer

Use one EC2 instance with a larger instance type

Answer

Use a single, large EC2 instance in one Availability Zone

Answer

Use multiple EC2 instances in one Availability Zone with health checks disabled

Question 3

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 4

A company wants to ensure that its application can recover from an Amazon S3 service disruption. The application reads and writes data to S3. Which strategy should the application implement to achieve resilience?

Accepted Answer

Implement application logic to fall back to an S3 bucket in a different Region if the primary bucket is unavailable. Implementing application logic to fall back to an S3 bucket in a different Region provides resilience against a regional S3 service disruption. S3 buckets are regional resources, so if one Region experiences an outage, the application can redirect reads and writes to a bucket in another Region. This approach requires the application to handle errors from the primary bucket and switch to the secondary bucket, ensuring continued availability without relying on automatic failover mechanisms that may not be instantaneous.

Answer

Store all data in a single S3 bucket with versioning enabled

Answer

Enable S3 Cross-Region Replication with automatic failover

Answer

Use S3 Transfer Acceleration to improve data transfer speed

Question 5

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 6

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 7

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 uses AWS-measured round-trip time data to direct each user to the AWS Region offering the fastest response, and each record can have an associated Route 53 health check; when the primary region's endpoint fails its health check, Route 53 automatically routes to the next lowest-latency healthy region. This combination of performance optimization and health-aware failover, without manual intervention, makes it the best fit for improving availability and performance across multiple regional ALBs. (Note: weighted routing policy also supports per-record health checks and will automatically exclude an unhealthy endpoint from rotation, redistributing traffic among the remaining healthy weighted records -- it is not correct that weighted routing requires manual updates to fail over.)

Answer

Weighted routing policy

Answer

Geolocation routing policy

Answer

Simple routing policy

Question 8

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 9

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 10

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

Question 11

A company runs a critical web application on EC2 instances in an Auto Scaling group. The application uses an Application Load Balancer (ALB) with health checks pointing to /health. Recently, the application experienced intermittent failures where the ALB would mark instances as unhealthy and route traffic away, causing a reduction in capacity. The development team noticed that the /health endpoint occasionally returns HTTP 503 when the application is under heavy load, but the application can recover quickly. The team wants to avoid unnecessary instance replacements while ensuring availability. Which solution should the DevOps engineer implement?

Accepted Answer

Increase the health check interval and increase the unhealthy threshold. Increasing the health check interval and increasing the unhealthy threshold makes the health check less sensitive to transient errors, such as occasional 503 responses under heavy load. This prevents unnecessary instance replacements while maintaining availability. Option A is incorrect because implementing a custom Lambda health check that ignores 503 responses would not leverage the built-in ALB health check tuning and adds complexity. Option B is incorrect because decreasing the unhealthy threshold would make instances more easily marked unhealthy, worsening the problem. Option D is incorrect because decreasing the health check interval increases the frequency of checks, which might cause more frequent detections of transient errors, and decreasing the healthy threshold does not address the issue of avoiding unnecessary replacements.

Answer

Implement a custom health check using Lambda that ignores 503 responses

Answer

Decrease the unhealthy threshold to mark instances unhealthy faster

Answer

Decrease the health check interval and decrease the healthy threshold

Question 12

A company has deployed a multi-tier application on AWS. The web tier uses an Auto Scaling group of EC2 instances behind an Application Load Balancer. The application tier uses another Auto Scaling group of EC2 instances that process messages from an Amazon SQS queue. The database tier uses Amazon RDS Multi-AZ. Recently, the application experienced a complete outage when the SQS queue became overwhelmed with messages due to a sudden spike in traffic. The application tier could not process messages fast enough, causing the queue to grow indefinitely and eventually exceed the visibility timeout, leading to message loss and degraded performance. The DevOps engineer needs to improve the resilience of the architecture to handle traffic spikes without losing messages. Which solution should be implemented?

Accepted Answer

Configure a dead-letter queue for unprocessed messages and implement Auto Scaling based on SQS queue depth. It addresses both the message loss and processing bottleneck. A dead-letter queue (DLQ) captures messages that cannot be processed successfully after a specified number of attempts, preventing them from being lost when the visibility timeout expires. Implementing Auto Scaling based on SQS queue depth (using a CloudWatch alarm on the ApproximateNumberOfMessagesVisible metric) dynamically adds more application-tier EC2 instances when the queue grows, ensuring the processing rate scales with demand and prevents the queue from being overwhelmed.

Answer

Limit the maximum message size and set a queue size limit to prevent overflow

Answer

Replace the standard SQS queue with a FIFO SQS queue to ensure exactly-once processing

Answer

Increase the visibility timeout in the SQS queue to allow more time for processing

Question 13

A company uses AWS Lambda with Amazon DynamoDB to process orders. During peak hours, the Lambda function sometimes fails with throttling errors from DynamoDB. The system must be resilient and cost-effective. What should a DevOps engineer do?

Accepted Answer

Configure DynamoDB auto scaling and implement a dead-letter queue in Lambda to retry failed events.. Configuring DynamoDB auto scaling allows the table to adjust its provisioned capacity based on actual traffic patterns, preventing throttling during peak hours while remaining cost-effective during low usage. Implementing a dead-letter queue (DLQ) in Lambda ensures that failed events (e.g., due to transient throttling) are captured and can be retried or investigated, providing resilience without manual intervention.

Answer

Use Amazon SQS to buffer the requests and have Lambda pull from the queue with a reserved concurrency limit.

Answer

Increase the DynamoDB provisioned read and write capacity units to a high fixed value.

Answer

Provision DynamoDB Accelerator (DAX) to cache reads and reduce throttling.

Question 14

A DevOps team is designing a disaster recovery plan for an RDS MySQL database. The database must be recoverable with minimal data loss in case of a regional failure. Which solution provides the LOWEST Recovery Point Objective (RPO)?

Accepted Answer

Configure a Cross-Region Read Replica.. A Cross-Region Read Replica provides the lowest Recovery Point Objective (RPO) because it uses asynchronous replication to continuously replicate data changes from the primary region to a replica in another region. In the event of a regional failure, you can promote the replica to a standalone primary database, typically losing only a few seconds to minutes of data, depending on replication lag. This minimizes data loss compared to snapshot-based or batch replication methods.

Answer

Take daily automated snapshots and copy them to another Region.

Answer

Use a Multi-AZ deployment with synchronous standby.

Answer

Use RDS Proxy to cache database writes.

Question 15

A company runs a stateless web application on Amazon ECS with Fargate. The application must be highly available across multiple Availability Zones. What is the BEST way to achieve this?

Accepted Answer

Create an ECS service with tasks in multiple AZs and place an ALB in front.. Running an ECS service with tasks in multiple Availability Zones (AZs) and placing an Application Load Balancer (ALB) in front ensures that if one AZ becomes unavailable, the ALB can route traffic to healthy tasks in the remaining AZs. This architecture provides both high availability and fault tolerance for the stateless web application, as the ALB performs health checks and distributes requests across tasks in different AZs.

Answer

Use an Auto Scaling group of EC2 instances in a single AZ and run ECS tasks on them.

Answer

Deploy a CloudFront distribution with multiple origins in different AZs.

Answer

Deploy a single ECS service with tasks in one AZ and use an ALB.