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

Question 1

A financial services company runs a critical application on Amazon ECS with Fargate launch type. The application has strict availability requirements and must survive an Availability Zone failure. The ECS service is configured with a desired count of 4 tasks, spread across two Availability Zones using a spread strategy. The service is fronted by an Application Load Balancer. During a recent AZ outage, one AZ became completely unavailable, but the application continued to serve traffic. However, after the AZ recovered, the ECS service did not automatically place new tasks in the recovered AZ to restore the desired count. The service remains with only 2 tasks in the remaining AZ. What is the most likely cause and solution?

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

Accepted Answer

The ECS service does not automatically replace tasks in a recovered AZ because the spread strategy is static. Manually update the service (e.g., force new deployment) to trigger rebalancing.. The ECS service uses a spread strategy, which maintains balance across AZs. When an AZ is unhealthy, ECS does not place tasks there. After recovery, the service may not automatically rebalance because the spread strategy is not proactive; it only ensures placement of new tasks. To force rebalancing, one can update the service (e.g., change desired count, then change back).

Answer

The Application Load Balancer is not health-checking the recovered AZ. Configure cross-zone load balancing.

Answer

The ECS service uses a spread strategy that does not automatically rebalance after an AZ recovers. Update the service to use a 'rebalance' strategy.

Answer

The ECS service is configured with a minimum healthy percent of 50%, which prevents replacement. Lower the minimum healthy percent to 0%.

Question 2

A startup runs a web application on EC2 instances behind an Application Load Balancer. They want to improve resilience by distributing instances across multiple Availability Zones. Currently, all instances are in us-east-1a. They create a launch template and an Auto Scaling group with a desired capacity of 2. They configure the Auto Scaling group to use two subnets: one in us-east-1a and one in us-east-1b. However, after updating, all instances remain in us-east-1a. What is the most likely reason?

Accepted Answer

The instance type is not available in us-east-1b.. The most likely reason is that the instance type specified in the launch template is not available in us-east-1b. Auto Scaling groups distribute instances across subnets, but if the instance type cannot be launched in a given Availability Zone, the group will place instances only in zones where the type is available. Option B is incorrect because the scenario explicitly states that the Auto Scaling group was configured to use two subnets, so the subnet configuration was updated. Option C is not the most likely cause because lack of internet route does not prevent instance launch. Option D is incorrect because launch templates do not specify subnets; subnet selection is configured in the Auto Scaling group.

Answer

The Auto Scaling group's subnet configuration was not updated to include the new subnet.

Answer

The new subnet in us-east-1b has no route to the internet.

Answer

The launch template specifies a single subnet in us-east-1a.

Question 3

A company runs a multi-tier web application on AWS. The application consists of an Application Load Balancer, EC2 instances in an Auto Scaling group, and an Amazon RDS Multi-AZ DB instance. The application experiences intermittent failures when the RDS primary instance fails over to the standby. The engineer needs to ensure that the application handles failover gracefully without manual intervention.

Accepted Answer

Use Amazon RDS Proxy to pool and reuse database connections, which reduces connection churn during failover.. Using a proxy like ProxySQL or configuring the application to use the RDS endpoint (which automatically points to the current primary) helps handle failover. Additionally, enabling RDS connection pooling or using Lambda to update the application can help, but the simplest is to use the instance endpoint with a retry mechanism.

Answer

Modify the application to use DNS caching with a TTL of 300 seconds to avoid stale DNS records.

Answer

Configure the Application Load Balancer to perform health checks on the RDS instance.

Answer

Enable Multi-AZ on the Auto Scaling group to ensure EC2 instances are in multiple AZs.

Question 4

A gaming company runs a real-time multiplayer game on AWS using Amazon EC2 instances in an Auto Scaling group behind a Network Load Balancer. The game state is stored in Amazon ElastiCache for Redis. The team needs to ensure that the architecture can survive a regional failure with minimal data loss and recovery time. The RTO is 15 minutes and RPO is 5 minutes. The game currently uses a single Redis cluster in us-east-1.

Accepted Answer

Configure Amazon ElastiCache for Redis with Global Datastore to replicate data to a second region.. Amazon ElastiCache Global Datastore provides fully managed, cross-Region replication for Redis clusters, enabling low-latency reads and disaster recovery across AWS Regions. This solution meets the RPO of 5 minutes by asynchronously replicating data from the primary region to a secondary region, and the RTO of 15 minutes by allowing a fast failover to the secondary cluster with minimal data loss.

Answer

Enable Multi-AZ on the ElastiCache cluster to improve availability within the region.

Answer

Use Amazon ElastiCache for Redis with cluster mode disabled to simplify failover.

Answer

Configure the application to write to the local Redis replica in the secondary region and then sync back.

Question 5

A company runs a static website on Amazon S3 with public read access. The website content is stored in an S3 bucket and served through an Amazon CloudFront distribution for better performance and security. Recently, the company noticed that some users are accessing the S3 bucket directly via the S3 endpoint, bypassing CloudFront. This increases costs and exposes the bucket to potential attacks. The company wants to ensure that all access to the website goes through CloudFront only. Which solution should the company implement?

Accepted Answer

Create an origin access identity (OAI) in CloudFront and update the S3 bucket policy to allow only the OAI to read objects.. To restrict access to the S3 bucket only through CloudFront, use an origin access identity (OAI) and a bucket policy that allows only the OAI. This way, direct access via S3 URL is denied.

Answer

Set the S3 bucket policy to deny all requests that do not come from the CloudFront distribution's IP addresses.

Answer

Configure the S3 bucket to use AWS WAF to block requests that do not have a custom header set by CloudFront.

Answer

Change the S3 bucket to be private and use presigned URLs for all requests.

Question 6

A company runs a serverless application using AWS Lambda functions that process messages from an Amazon SQS queue. The function scales up to handle high traffic but sometimes experiences throttling errors (HTTP 429) from Lambda. The company wants to improve the resilience of the application by reducing throttling. The SQS queue is configured as a Lambda event source with a batch size of 10. The Lambda function has a reserved concurrency of 100. Which combination of actions will best reduce throttling? (Choose the single best answer.)

Accepted Answer

Increase the Lambda function's reserved concurrency to 500.. Throttling errors (HTTP 429) occur when Lambda function invocations exceed the account-level concurrency limit or the function's reserved concurrency. By increasing the reserved concurrency from 100 to 500, the function can handle more concurrent invocations, reducing the likelihood of throttling when traffic spikes. This directly addresses the scaling bottleneck without changing the event source or message processing pattern.

Answer

Change the SQS queue to use a FIFO queue to guarantee exactly-once processing.

Answer

Increase the SQS batch size to 50 to process more messages per invocation.

Answer

Use a dead-letter queue (DLQ) for unprocessed messages and set up a CloudWatch alarm to trigger a second Lambda function to reprocess them.

Question 7

A company runs a critical web application on EC2 instances behind an Application Load Balancer (ALB) with Auto Scaling. During a recent traffic spike, the application became unavailable for 10 minutes. Analysis shows that the ALB's healthy host count dropped to zero because the instances failed health checks due to high CPU load. What is the MOST effective design change to improve resilience during future traffic spikes?

Accepted Answer

Use predictive scaling with a scheduled scaling policy for known peak times.. Predictive scaling uses historical traffic data to forecast future demand and proactively adjust capacity before a spike occurs. This prevents the CPU from reaching critical levels that cause health check failures, ensuring the ALB always has healthy hosts. Scheduled scaling alone would not adapt to unexpected spikes, but predictive scaling combined with dynamic scaling provides both proactive and reactive resilience.

Answer

Increase the instance size to handle higher load.

Answer

Configure step scaling policies based on CPU utilization.

Answer

Set a higher CPU threshold for health checks.

Question 8

A company runs a stateful web application on EC2 instances behind a Network Load Balancer (NLB) in a single Availability Zone. The application stores session state locally on the instance. The company wants to achieve high availability across multiple AZs with minimal application changes. What should the DevOps engineer do?

Accepted Answer

Replace the NLB with an ALB and enable sticky sessions (session affinity) using the ALB's cookie.. Replacing the NLB with an ALB and enabling sticky sessions (session affinity) using the ALB's cookie allows the stateful web application to maintain session state across multiple AZs without modifying the application code. The ALB generates a cookie (AWSALB) that binds a client's session to a specific target instance, ensuring subsequent requests from the same client are routed to the same EC2 instance. This achieves high availability across AZs with minimal changes, as the application continues to store session state locally on the instance.

Answer

Add more AZs and configure the NLB with cross-zone load balancing.

Answer

Replace the NLB with an ALB and use ElastiCache for session storage.

Answer

Use a Multi-AZ RDS instance to store session state.

Question 9

A company's DevOps team is designing a disaster recovery plan for a critical application. The application runs on EC2 instances with an RDS MySQL database. The Recovery Time Objective (RTO) is 15 minutes, and the Recovery Point Objective (RPO) is 1 hour. Which approach BEST meets these requirements?

Accepted Answer

Use a multi-Region application with Route 53 latency-based routing and RDS read replicas in the DR Region.. The best approach for a multi-Region disaster recovery with RTO of 15 minutes and RPO of 1 hour. By deploying the application in multiple regions and using RDS cross-Region read replicas, data is asynchronously replicated with an RPO typically within seconds to minutes, well within 1 hour. In the event of a failure, the read replica can be promoted to a primary instance, and Route 53 routing (preferably failover routing, but latency-based routing can also redirect traffic) can shift traffic to the DR region. This failover can be completed within a few minutes, meeting the 15-minute RTO. Option A fails because daily snapshots exceed the 1-hour RPO and restore times exceed the RTO. Option C incorrectly relies on RDS Multi-AZ, which is a single-region high-availability feature and does not provide cross-region replication; thus it cannot serve as a disaster recovery solution across regions. Option D, pilot light with snapshots, has a longer RTO as it requires restoring instances from snapshots and starting them, likely exceeding 15 minutes.

Answer

Use backup and restore with daily snapshots stored in S3 and cross-Region replication.

Answer

Use a warm standby strategy with a scaled-down copy of the production environment in the DR Region, and replicate data using RDS Multi-AZ with synchronous replication.

Answer

Use a pilot light strategy with EC2 instances stopped and RDS snapshots copied to the DR Region.

Question 10

A company's application uses Amazon SQS to decouple microservices. During peak hours, the SQS queue backlog grows significantly, causing processing delays. The DevOps team wants to reduce latency without increasing costs unnecessarily. What should the team do?

Accepted Answer

Configure Auto Scaling for the consumer fleet based on the ApproximateNumberOfMessagesVisible metric.. Scaling the consumer fleet based on the ApproximateNumberOfMessagesVisible metric directly addresses the backlog by adding more processing capacity when the queue grows. This approach reduces latency dynamically without incurring unnecessary costs during off-peak hours, as it only scales up when needed. Auto Scaling with SQS metrics is a cost-effective, elastic solution for handling variable workloads.

Answer

Increase the visibility timeout to allow consumers more time to process messages.

Answer

Use an SQS queue with priority settings to process high-priority messages first.

Answer

Increase the SQS queue's throughput by requesting a quota increase.

Question 11

A company wants to design a highly available web application using AWS services. The application must be resilient to the failure of an entire AWS Region. Which THREE components should the architecture include? (Choose THREE.)

Accepted Answer

Amazon Route 53 with a failover routing policy.. Amazon Route 53 with a failover routing policy is correct because it enables DNS-based health checking and automatic traffic routing to a secondary region when the primary region becomes unavailable. This is essential for cross-region disaster recovery, as Route 53 can monitor endpoint health and update DNS records to direct users to the healthy region, ensuring application availability despite a full region failure.

Answer

An Application Load Balancer (ALB) deployed in one Region.

Answer

Amazon EC2 instances in a single Region.

Question 12

A company runs a critical e-commerce platform on AWS. The architecture includes an Application Load Balancer (ALB) that distributes traffic to a fleet of EC2 instances in an Auto Scaling group across three Availability Zones. The instances run a Java application that connects to an Amazon RDS Multi-AZ MySQL database. The application also uses Amazon ElastiCache for Redis for session caching. The company recently experienced a severe outage where the ALB's 5xx error rate spiked to 100% for 45 minutes. The root cause was a combination of a slow-running query on the RDS primary instance and a subsequent failover that caused the application to lose connections to the database. The failover happened because the slow query caused the primary to become unresponsive, triggering a Multi-AZ failover. During the failover, the application's connection pool exhausted, and new connections failed. The application logs show a high rate of 'java.sql.SQLTimeoutException' and 'com.mysql.cj.exceptions.CJCommunicationsException'. The DevOps team needs to implement a long-term solution that minimizes the impact of similar incidents. The solution must be cost-effective and require minimal application changes. Which combination of actions should the DevOps team take?

Accepted Answer

Implement Amazon RDS Proxy to manage database connections and add read replicas to offload read traffic.. Amazon RDS Proxy is the correct solution because it efficiently manages database connection pooling, reducing the likelihood of connection exhaustion during failovers. By maintaining a warm connection pool and automatically reconnecting to the new primary after a Multi-AZ failover, RDS Proxy minimizes application-side connection timeouts and errors like SQLTimeoutException and CJCommunicationsException. Adding read replicas offloads read traffic, reducing the load on the primary and mitigating the risk of slow queries causing unresponsiveness. This combination requires minimal application changes and is cost-effective compared to scaling the primary instance.

Answer

Use an Auto Scaling policy for EC2 based on RDS connection count and implement a read replica for the primary.

Answer

Configure Multi-AZ RDS with a synchronous standby and use Amazon RDS for MySQL with enhanced monitoring.

Answer

Increase the instance size of the RDS primary and enable Performance Insights to identify slow queries.

Question 13

A company runs a containerized microservices application on Amazon EKS. The application includes a critical service that processes real-time financial transactions. This service must be highly available and resilient to node failures. The current setup uses a Deployment with 3 replicas and a ClusterIP service. During a recent node failure, the application experienced a brief period of unavailability. Which action should the DevOps engineer take to improve resilience without changing the underlying infrastructure?

Accepted Answer

Configure a PodDisruptionBudget with a maxUnavailable of 1, and add pod anti-affinity rules to spread pods across different nodes.. A PodDisruptionBudget with maxUnavailable=1 ensures that at most one pod is unavailable during voluntary disruptions, while pod anti-affinity rules force the scheduler to distribute pods across different nodes. This combination prevents a single node failure from taking down all replicas, maintaining service availability without altering the underlying infrastructure.

Answer

Change the service type from ClusterIP to NodePort and configure an external load balancer.

Answer

Increase the number of replicas to 10 and use a node selector to schedule all pods on the largest instance type.

Answer

Enable HorizontalPodAutoscaler with a target CPU utilization of 50% to automatically scale the Deployment.

Question 14

A company is building a multi-tier web application on AWS. The application must be resilient to the failure of an entire Availability Zone. The architecture includes an Application Load Balancer (ALB), EC2 instances in an Auto Scaling group, and an Amazon RDS for MySQL database. Which TWO actions should be taken to achieve this resilience? (Choose two.)

Accepted Answer

Configure the Auto Scaling group to launch EC2 instances in at least two Availability Zones.. Configuring the Auto Scaling group to launch EC2 instances in at least two Availability Zones ensures that if one AZ fails, the remaining AZ(s) can continue serving traffic. This is a fundamental pattern for building AZ-resilient compute tiers. Option E is correct because deploying Amazon RDS for MySQL in a Multi-AZ configuration automatically provisions and maintains a synchronous standby replica in a different AZ, providing automatic failover if the primary DB instance fails, thus ensuring database resilience.

Answer

Configure an RDS read replica in a different Availability Zone.

Answer

Use a Single-AZ RDS for MySQL database to keep costs low.

Answer

Place all EC2 instances in the same Availability Zone to reduce cross-AZ data transfer costs.

Question 15

A company runs a critical web application on Amazon EC2 instances behind an Application Load Balancer (ALB) across multiple Availability Zones. The application stores session data in a shared Amazon ElastiCache for Redis cluster. The operations team reports that during a recent AZ failure, users experienced session loss and application errors. Which combination of actions should the company take to improve resilience and maintain session state during an AZ failure? (Choose TWO.)

Accepted Answer

Configure the ALB with cross-zone load balancing enabled and connection draining set to a suitable timeout.. Enabling cross-zone load balancing on the ALB ensures traffic is distributed evenly across all EC2 instances in all AZs, and connection draining with a suitable timeout allows in-flight requests to complete before instances are deregistered, preventing session loss during an AZ failure. Option C is correct because enabling cluster mode for ElastiCache for Redis with replica nodes in different AZs provides automatic sharding and replication, ensuring session data remains available and consistent even if a primary node in one AZ fails. Option E is incorrect because while ElastiCache for Redis supports Multi-AZ with automatic failover, it alone does not guarantee that replica nodes are placed in different Availability Zones for each shard; enabling cluster mode with replicas in different AZs (Option C) provides a more comprehensive solution for maintaining session state during an AZ failure.

Answer

Deploy an Auto Scaling group with a dynamic scaling policy that adds instances in the remaining AZs.

Answer

Configure the application to use a custom DNS name with a low TTL pointing to the ElastiCache cluster endpoint.

Answer

Enable Multi-AZ for the ElastiCache cluster to automatically fail over to a replica in another AZ.