DOP-C02 Resilient Cloud Solutions Practice Test 12 — 15 Questions

Question 1

A company uses AWS Lambda to process messages from an SQS queue. They need to ensure that if the Lambda function fails, the message is not lost and can be processed again. Which configuration is required?

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

Accepted Answer

Set the Lambda event source mapping to not delete messages from the queue on failure.. The Lambda event source mapping for SQS can be configured to not delete messages from the queue if the function fails. This ensures that the message remains in the queue and becomes visible again after the visibility timeout expires, allowing it to be retried. Without this setting, Lambda automatically deletes messages upon successful processing, but on failure, the default behavior is to delete them as well, which would cause message loss.

Answer

Set the visibility timeout to less than the Lambda function timeout.

Answer

Enable SQS redrive policy to retry messages.

Answer

Configure a dead-letter queue (DLQ) on the SQS queue.

Question 2

A company runs a critical application on EC2 instances in an Auto Scaling group behind an ALB. They want to ensure that if an instance fails, the application remains available with minimal disruption. Which combination of services provides the best resilience?

Accepted Answer

Auto Scaling group with ELB health checks and multiple AZs.. Deploying an Auto Scaling group across multiple Availability Zones (AZs) with Elastic Load Balancer (ALB) health checks ensures that if an EC2 instance fails in one AZ, the ALB automatically routes traffic to healthy instances in other AZs, and Auto Scaling replaces the failed instance. This combination provides both fault isolation and automated recovery, minimizing disruption to the application.

Answer

Auto Scaling group with minimum 2 in a single AZ.

Answer

EC2 instance recovery with CloudWatch alarms.

Answer

Auto Scaling group with desired capacity of 2 and a lifecycle hook.

Question 3

A company wants to design a resilient architecture for a web application using AWS services. Which of the following is a best practice for improving resilience?

Accepted Answer

Deploy EC2 instances in multiple Availability Zones.. Deploying EC2 instances across multiple Availability Zones (AZs) is a fundamental best practice for resilience because it eliminates a single point of failure at the data center level. If one AZ experiences an outage, traffic can be automatically routed to healthy instances in other AZs via an Elastic Load Balancer (ELB), ensuring application availability. This approach aligns with the AWS Well-Architected Framework's Reliability Pillar, which mandates distributing workloads across multiple AZs to achieve high availability.

Answer

Use an Auto Scaling group in a single AZ.

Answer

Use a single AZ with RDS Multi-AZ.

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Use one large EC2 instance to handle all traffic.

Question 4

A company is designing a multi-region disaster recovery strategy for a stateless web application. They want to minimize RTO and RPO. Which TWO of the following should they implement? (Choose TWO.)

Accepted Answer

Use cross-region replication for data stores.. Cross-region replication for data stores ensures that data is continuously synchronized to a secondary AWS region, minimizing Recovery Point Objective (RPO) to near-zero and reducing Recovery Time Objective (RTO) as the data is already available in the DR region. This approach avoids the need to restore from backups, which would increase RTO and potentially lose recent transactions.

Answer

Use a passive standby in a single Availability Zone.

Answer

Perform periodic backups and restore in the DR region.

Answer

Configure cross-region read replicas for the database.

Question 5

A company uses Amazon ECS with Fargate for containerized applications. They need to ensure that if a task fails, it is automatically restarted and the application remains available. Which THREE actions should they take? (Choose THREE.)

Accepted Answer

Configure the ECS service to automatically restart failed tasks.. Amazon ECS services can be configured with a desired task count and a task placement strategy that automatically replaces any failed or stopped tasks. When a task exits unexpectedly, the ECS service scheduler detects the discrepancy between the desired and running count and launches a new task to maintain availability. This is the native mechanism for self-healing in ECS, without requiring external triggers.

Answer

Set up a CloudWatch alarm to trigger AWS Lambda to restart tasks.

Answer

Configure an EC2 Auto Scaling group for the ECS cluster.

Question 6

Refer to the exhibit. An IAM policy is attached to a user. A developer tries to upload an object to s3://my-bucket/confidential/report.pdf without specifying server-side encryption. What will happen?

Accepted Answer

The upload fails because the Deny statement requires SSE-KMS.. The upload fails because the Deny statement in the IAM policy explicitly denies the s3:PutObject action unless the request includes the s3:x-amz-server-side-encryption header with a value of 'aws:kms'. When the developer does not specify server-side encryption, the condition is not met, so the Deny applies, causing the upload to fail. Option A is incorrect because the Allow statement does not override an explicit Deny. Option B is incorrect because the condition key is correct; the failure is due to the missing encryption header. Option D is incorrect because the Deny is not based on the object name prefix; it applies to all objects in the bucket.

Answer

The upload succeeds because the Allow statement grants PutObject.

Answer

The upload succeeds because the Deny condition uses a wrong condition key.

Answer

The upload fails only if the object name matches the prefix.

Question 7

A company runs a high-traffic e-commerce application on EC2 instances in an Auto Scaling group behind an ALB. The application uses an in-memory cache on the EC2 instances. During a recent deployment, the Auto Scaling group terminated an instance that had active user sessions, causing users to lose their cart data and leading to a poor customer experience. The company wants to prevent this in future deployments. They need a solution that allows existing sessions to complete before instance termination, without manual intervention. Which solution should they use?

Accepted Answer

Implement an Auto Scaling lifecycle hook that puts the instance in a 'terminating:wait' state, and have a script on the instance that signals completion after draining sessions.. An Auto Scaling lifecycle hook puts the instance into a 'terminating:wait' state when the ASG decides to terminate it, pausing the termination process. A script on the instance can then drain active sessions (e.g., finish processing requests, flush cart data to a persistent store) and call CompleteLifecycleAction to signal completion, after which the ASG proceeds with termination. This is the only option that provides a programmable, instance-level mechanism to gracefully complete sessions before termination without manual intervention.

Answer

Increase the Auto Scaling group's cooldown period and health check grace period.

Answer

Enable connection draining on the ALB target group and increase the deregistration delay.

Answer

Change the health check type to ELB and mark instances unhealthy before deployment.

Question 8

A company has a microservices architecture running on Amazon ECS with Fargate launch type. Each service is deployed in multiple Availability Zones. The services communicate via REST APIs. Recently, a downstream service experienced a partial outage, causing upstream services to time out and leading to cascading failures. The team wants to improve resilience against such failures. Which combination of actions should the DevOps engineer take? (Choose TWO.)

Accepted Answer

Implement circuit breaker patterns in the service clients.. Option B is correct because a circuit breaker in the service clients detects repeated failures from a downstream dependency and trips open, failing fast instead of letting upstream threads block on slow REST calls, which directly prevents the timeout propagation and cascading failures described. Option D is correct because moving to asynchronous communication with Amazon SQS or Amazon EventBridge decouples services: upstream services enqueue or publish events and return immediately, so a partial outage in a downstream consumer no longer blocks callers, and messages can be retried or buffered until the consumer recovers. Option A is not appropriate because increasing HTTP timeouts makes callers wait longer, consuming threads and connections and worsening cascading failures rather than containing them. Option C is wrong because removing retry logic eliminates a useful resilience mechanism for transient errors; retries should be bounded and combined with circuit breakers and backoff, not deleted. Option E is not the right fix because scaling on request count does not address a downstream dependency that is failing or slow, and could even amplify load against the impaired service.

Answer

Increase the HTTP timeout values for all service-to-service calls.

Answer

Remove all retry logic from service calls.

Answer

Configure Auto Scaling for all services based on request count.

Question 9

A company runs a serverless application using AWS Lambda functions behind an Amazon API Gateway. The application processes user uploads stored in an S3 bucket. The Lambda function writes results to a DynamoDB table. Recently, the function started timing out when processing large files. What should the DevOps engineer do to improve resilience for large file processing?

Accepted Answer

Use S3 event notifications to trigger an AWS Step Functions workflow that processes the file asynchronously.. Using S3 event notifications to trigger an AWS Step Functions workflow enables asynchronous processing of large files, decoupling the upload from the processing and avoiding Lambda's timeout limits. Option A (increasing memory) may improve CPU performance but does not address the timeout issue for large files. Option C (increasing timeout) can extend up to 15 minutes, but large files may still exceed this limit and it does not provide a resilient architecture. Option D (ElastiCache) caches processed results but does not solve the initial timeout problem; it is irrelevant to the large file processing issue.

Answer

Increase the Lambda function memory to improve CPU performance.

Answer

Increase the Lambda function timeout to the maximum 15 minutes.

Answer

Add Amazon ElastiCache to cache processed results and reduce Lambda execution time.

Question 10

Your company runs a multi-tier web application on AWS. The web tier consists of EC2 instances behind an Application Load Balancer (ALB) in an Auto Scaling group across three Availability Zones. The application tier runs on a separate Auto Scaling group of EC2 instances that process requests from the web tier. The database tier uses an Amazon RDS for PostgreSQL Multi-AZ deployment. All application servers write logs to Amazon CloudWatch Logs. Recently, the operations team reported that during peak hours, the web tier experiences intermittent 503 errors. The ALB access logs show that the errors occur when the target group's healthy host count drops to zero momentarily. The Auto Scaling group's minimum and desired capacity is 6, with a maximum of 12. The scaling policy is based on average CPU utilization, with a target of 60%. The health check grace period is 300 seconds. The application health check endpoint returns a 200 status when healthy. The DevOps engineer suspects that the scaling policy is too slow to react to traffic spikes. The engineer wants to implement a more proactive scaling approach. Which solution should the engineer implement?

Accepted Answer

Implement a predictive scaling policy combined with dynamic scaling to proactively adjust capacity based on forecasted traffic.. Predictive scaling uses machine learning to forecast future traffic based on historical patterns and proactively provisions capacity ahead of predicted demand, which directly addresses the slow reaction of reactive CPU-based scaling. Combining predictive scaling with dynamic scaling provides both proactive baseline capacity and reactive adjustments for unexpected spikes. This is the AWS-recommended approach for cyclical traffic patterns with intermittent 503 errors caused by insufficient capacity during peaks.

Answer

Implement a scheduled scaling policy that increases capacity 30 minutes before the expected peak.

Answer

Increase the health check grace period to 600 seconds to give new instances more time to become healthy.

Answer

Switch to a step scaling policy with a lower cooldown period and a greater scaling adjustment.

Question 11

A startup runs a stateless web application on AWS Elastic Beanstalk with a single environment. The application uses an Amazon RDS for MySQL database instance. The startup is preparing for a marketing campaign that is expected to increase traffic by 10x. The CTO is concerned about the application's ability to handle the load and wants to ensure high availability and resilience. The current architecture has a single RDS instance (db.t3.medium) and a single Elastic Beanstalk environment with one EC2 instance (t3.medium). The startup has a limited budget but wants to improve resilience without over-provisioning. Which combination of actions should the DevOps engineer recommend? (Choose THREE.)

Accepted Answer

Switch the Elastic Beanstalk environment to a load-balanced, auto-scaled environment with a minimum of 2 instances across 2 Availability Zones.. Option C is correct because converting the single-instance Elastic Beanstalk environment to a load-balanced, auto-scaled environment with a minimum of two instances across two Availability Zones removes the single point of failure at the web tier and lets the environment scale horizontally to absorb the 10x traffic spike. Option D is correct because enabling Multi-AZ on the RDS for MySQL instance creates a synchronous standby replica in a second AZ with automatic failover, improving database resilience without requiring application changes. Option E is correct because RDS Proxy pools and shares database connections, which prevents the connection exhaustion and overhead that occur when many new EC2 instances and users open connections directly to MySQL during a traffic surge. Option A is not among the marked answers, and while caching could reduce read load, it is not required to achieve the stated high availability and resilience goals. Option B is not marked correct because dedicated instances raise cost and do not provide the multi-AZ redundancy or elasticity that the scenario demands.

Answer

Add an Amazon ElastiCache cluster to cache frequent database queries.

Answer

Use dedicated instances for the EC2 instances to ensure consistent performance.

Question 12

A company runs a stateful web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application stores session data in local instance memory. To improve resiliency, the company wants to make the application stateless and distribute the load across multiple Availability Zones. Which THREE actions should the company take? (Choose three.)

Accepted Answer

Configure the ALB to distribute traffic across EC2 instances in multiple Availability Zones.. Option C is correct because an ALB is a regional load balancer that can register targets in multiple Availability Zones, so configuring it to distribute traffic across EC2 instances in several AZs removes the single-AZ failure point and improves resiliency. Option D is correct because moving session data out of local instance memory into an Amazon ElastiCache cluster (e.g., Redis or Memcached) externalizes session state, allowing any instance in any AZ to serve any request and making the application stateless. Option E is correct because Amazon DynamoDB is a fully managed, multi-AZ, highly durable key-value store that can also hold session state externally, achieving the same stateless design without relying on instance memory. Option A is not appropriate because sticky sessions keep a user bound to a single instance and actually perpetuate statefulness rather than eliminate it. Option B is not appropriate because replacing the ALB with an NLB does not address session state at all and an NLB lacks the HTTP/HTTPS layer-7 routing features typically used by web applications.

Answer

Enable sticky sessions (session affinity) on the ALB.

Answer

Replace the ALB with a Network Load Balancer (NLB) to improve performance.

Question 13

A company runs a production application on Amazon ECS with Fargate, fronted by an Application Load Balancer (ALB). The application experiences periodic latency spikes and occasional 502 errors. The ECS service is configured with a desired count of 2 tasks, and the ALB health check is set to /health with a 30-second interval and 2 consecutive failures threshold. The team uses CloudWatch Container Insights and has noticed that CPU and memory utilization of tasks remain below 50%. However, the ALB TargetGroup's HealthyHostCount metric occasionally drops to 0 for a few minutes before recovering. The deployment strategy is rolling update with a minimum healthy percent of 50% and maximum percent of 200%. The team recently updated the task definition to increase memory and CPU, but the issue persists. What is the MOST likely cause of the problem?

Accepted Answer

The ALB health check is too aggressive, causing tasks to be marked unhealthy during brief initialization or deployment.. The health check interval (30 seconds) and failure threshold (2) mean it takes up to 60 seconds to mark a task unhealthy. During deployments, the rolling update may temporarily have only 1 healthy task (minimum 50% of 2 = 1), and if that task becomes unhealthy, HealthyHostCount drops to 0. Option A is wrong because CPU and memory are below 50%, so resource limits are not the issue. Option C is wrong because a target group with 2 tasks and 2 AZs is fine; the problem is not AZ-specific. Option D is wrong because ECS service-linked role does not affect health checks.

Answer

The ECS service role lacks permissions to register targets with the ALB.

Answer

The ALB target group is configured with only one Availability Zone, causing loss of all targets when that AZ fails.

Answer

The task's CPU or memory limits are set too low, causing the container to be throttled.

Question 14

A company uses Amazon RDS Multi-AZ for disaster recovery. The primary DB instance in us-east-1a fails. What happens next?

Accepted Answer

The standby DB instance in us-east-1b is promoted automatically and the CNAME record is updated. RDS Multi-AZ maintains a synchronous standby replica in a different AZ and performs automatic failover by promoting the standby and updating the DB instance's DNS CNAME to point to the new primary. The failover is triggered by the primary's failure and typically completes in 60–120 seconds, with no manual intervention required. Applications using the endpoint hostname reconnect transparently once DNS TTL expires.

Answer

The administrator must manually promote the standby instance

Answer

The primary instance is automatically rebuilt in the same AZ

Answer

A read replica in us-east-1b is automatically promoted to primary

Question 15

A company has a stateless web application on EC2 instances behind an ALB. They want to ensure that if an entire Availability Zone fails, the application remains available with minimal impact. Which architecture best meets this requirement?

Accepted Answer

Deploy the application in two AZs with an Auto Scaling group and an ALB that is enabled for multiple AZs. The correct architecture deploys the stateless application across two Availability Zones using an Auto Scaling group that spans both AZs, and an Application Load Balancer (ALB) configured with subnets in both AZs. If one AZ fails, the ALB automatically routes traffic to healthy instances in the surviving AZ, and the Auto Scaling group maintains capacity. This provides high availability with minimal impact, as required.

Answer

Use a global secondary index in DynamoDB to replicate data across regions

Answer

Deploy EC2 instances in two AZs but use a single-AZ ALB

Answer

Deploy the application in a single AZ with an Auto Scaling group that launches instances in the same AZ