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As described in the AWS Cloud Operations and EC2 Management documentation, changing an instance type (e.g., from T3 to C5) requires that the instance be stopped first. Once stopped, the engineer can modify the instance type through the AWS Management Console, CLI, or API, then start the instance again to apply changes.

This process preserves the root volume, networking configuration, and data, making it an operationally safe and efficient way to upgrade to a different instance family.

Changing the instance type while running (Option D) is unsupported. VM Import/Export (Option A) is for external VM migration. Hibernation (Option B) does not apply to type changes.

Thus, Option C is correct — stopping the instance, changing its type, and restarting it meets AWS best practices.

According to the AWS Cloud Operations and ElastiCache documentation, cache evictions occur when the cache runs out of memory and must remove items to make space for new data.

To reduce evictions and retain frequently accessed items, AWS recommends increasing the total available memory — either by scaling up to larger node types or scaling out by adding shards/nodes. Migrating to a cluster with larger nodes is the simplest and most efficient solution because it immediately expands capacity without architectural changes.

Adjusting TTL (Options B and C) controls expiration timing, not memory allocation. Adding a single node (Option A) may help, but redistributing data requires resharding, introducing more complexity.

Thus, Option D provides the lowest operational overhead and ensures high cache hit rates by increasing total cache memory.

Per the AWS Cloud Operations and EventBridge documentation, when events are sent across AWS accounts — particularly from multiple accounts in an AWS Organization — the target event bus in the receiver account must include a resource-based policy that explicitly allows events:PutEvents API calls from the sender accounts or the organization ID.

Even if the sender accounts have IAM permissions to call PutEvents, the receiving event bus must trust those accounts via a resource policy. Without this configuration, EventBridge automatically rejects incoming cross-account events, and those events never reach the target Lambda function for processing.

AWS guidance states that “Cross-account event delivery requires a resource-based policy on the event bus that grants permissions to the source accounts or organization.” The policy can include either individual AWS account IDs or the organization’s root ID.

In this scenario, because the events originate from multiple accounts and there is no resource policy on the target event bus to authorize those sender accounts, the events are not delivered.

Therefore, the correct cause is C – the resource-based policy on the target event bus must be modified to allow PutEvents API calls from the sender accounts.

Comprehensive and Detailed Explanation From Exact Extract of AWS CloudOps Doocuments:

For high availability and fast failover, ElastiCache for Redis supports replication groups with Multi-AZ and automatic failover. CloudOps guidance states that a primary node can be paired with one or more replicas across multiple Availability Zones; if the primary fails, Redis automatically promotes a replica to primary in seconds, thereby minimizing RTO. This architecture maintains in-memory data continuity without waiting for backup restore operations. Backups (Options B and D) provide durability but require restore and re-warm procedures that increase RTO and may impact application latency. Switching engines (Option A) to Memcached does not provide Redis replication/failover semantics and would not inherently improve resilience for this use case. Therefore, creating a read replica in a different AZ and enabling Multi-AZ with automatic failover is the prescribed CloudOps pattern to increase resilience and achieve the lowest practical RTO for Redis caches.

References (AWS CloudOps Documents / Study Guide):

• AWS Certified CloudOps Engineer – Associate (SOA-C03) Exam Guide – Reliability and Business Continuity

• Amazon ElastiCache for Redis – Replication Groups, Multi-AZ, and Automatic Failover

• AWS Well-Architected Framework – Reliability Pillar

According to the AWS Cloud Operations and EC2 Connectivity documentation, EC2 Instance Connect Endpoint allows access to instances without internet exposure or open SSH ports. However, for successful connectivity, the EC2 instance must have Systems Manager permissions through an IAM instance profile.

If no IAM instance profile is attached, the instance cannot establish a control channel with the Systems Manager service, and EC2 Instance Connect cannot authenticate the session.

Opening port 22 (Option B) is unnecessary and contradicts the private subnet design. HTTPS rules (Option A) are irrelevant because EC2 Instance Connect communicates through AWS APIs, not direct HTTPS connections. Recreating the instance with a key pair (Option D) bypasses the intended keyless connection mechanism.

Therefore, Option C — attaching an IAM instance profile with Systems Manager permissions — enables secure, private access through EC2 Instance Connect Endpoint.

High availability requires removing single-AZ risk and eliminating manual recovery. The AWS Reliability best practices state to design for multi-AZ and automatic healing: Auto Scaling “helps maintain application availability and allows you to automatically add or remove EC2 instances” (AWS Auto Scaling User Guide). The Reliability Pillar recommends to “distribute workloads across multiple Availability Zones” and to “automate recovery from failure” (AWS Well-Architected Framework – Reliability Pillar). Attaching the Auto Scaling group to an ALB target group enables health-based replacement: instances failing load balancer health checks are replaced and traffic is routed only to healthy targets. Using an AMI in a launch template ensures consistent, repeatable instance configuration (AWS EC2 Launch Templates). Options A and C keep all instances in a single Availability Zone and rely on manual or ad-hoc restarts, which do not meet high-availability or resiliency goals. Option B only scales vertically and adds a restart rule; it neither removes the single-AZ failure domain nor provides automated replacement. Therefore, creating a multi-AZ EC2 Auto Scaling group with a launch template and attaching it to the ALB target group (Option D) is the CloudOps-aligned solution for resilience and business continuity.

References (AWS CloudOps Documents / Study Guide):

• AWS Certified CloudOps Engineer – Associate (SOA-C03) Exam Guide: Domain 2 – Reliability and Business Continuity

• AWS Well-Architected Framework – Reliability Pillar

• Amazon EC2 Auto Scaling User Guide – Health checks and replacement

• Elastic Load Balancing User Guide – Target group health checks and ALB integration

• Amazon EC2 Launch Templates – Reproducible instance configuration

The Storage Gateway service enables hybrid cloud backup by presenting local block storage that synchronizes with AWS cloud storage. For scenarios where all data must remain available locally while still backed up to AWS, the correct mode is gateway-stored volumes.

AWS documentation defines:

“Use stored volumes if you want to keep all your data locally while asynchronously backing up point-in-time snapshots to Amazon S3 for durable storage.”

These volumes expose an iSCSI interface compatible with POSIX file systems, allowing direct use by on-premises backup software.

Gateway-cached volumes (Option C) store primary data in AWS with limited local cache, violating the “all data must be available locally” requirement. Options A and B are object-based storage solutions, not compatible with POSIX or block-based backup applications.

Therefore, Option D fully satisfies CloudOps reliability and continuity best practices by ensuring local availability, cloud durability, and POSIX compatibility for backups.

References (AWS CloudOps Documents / Study Guide):

• AWS Certified CloudOps Engineer – Associate (SOA-C03) Exam Guide – Domain 2: Reliability and Business Continuity

• AWS Storage Gateway User Guide – Stored Volumes Overview

• AWS Well-Architected Framework – Reliability Pillar

• AWS Hybrid Cloud Storage Best Practices

The AWS Cloud Operations and Storage documentation confirms that S3 Transfer Acceleration is designed to increase upload speed for objects transferred to S3 buckets over long distances.

It uses AWS Global Edge Network and Amazon CloudFront edge locations to route data through optimized network paths, reducing latency and achieving higher throughput compared to standard S3 uploads.

After enabling Transfer Acceleration on the bucket, users upload files to the accelerated endpoint (e.g., bucketname.s3-accelerate.amazonaws.com). This feature requires no changes to application logic besides endpoint modification and provides immediate performance improvement.

CloudFront (Option A) is for content delivery, not uploads. ElastiCache (Option B) and Global Accelerator (Option C) are unrelated to S3 upload performance.

Thus, Option D is correct — enable S3 Transfer Acceleration for faster, optimized file uploads.

According to the AWS Cloud Operations and Networking documentation, instances in a private subnet do not have a direct route to the internet gateway and thus require a NAT gateway for outbound internet access.

The correct configuration is to create a NAT gateway in the public subnet, associate an Elastic IP address, and then update the private subnet’s route table to send all 0.0.0.0/0 traffic to the NAT gateway. This enables instances in the private subnet to initiate outbound connections while keeping inbound traffic blocked for security.

Placing the NAT gateway inside the private subnet (Options C or D) prevents connectivity because it would not have a route to the internet gateway. Configuring routes from the public subnet to the NAT gateway (Option B) does not serve private subnet traffic.

Hence, Option A follows AWS best practices for enabling secure, managed, outbound-only internet access from private resources.

AWS CloudOps automation best practices recommend using AWS Systems Manager Quick Setup for organization-wide management and configuration of EC2 instances. The Default Host Management Configuration Quick Setup automatically enables Systems Manager capabilities such as Patch Manager, Inventory, Session Manager, and Automation across all managed instances within the organization.

When deployed from the management account, Quick Setup automatically integrates with AWS Organizations to propagate configuration and permissions to existing and future accounts. This meets the requirement for organization-wide management with no manual configuration or SSH access. AWS documentation notes:

“You can use Quick Setup in the management account of an organization in AWS Organizations to configure Systems Manager capabilities for all accounts and Regions. Quick Setup automatically keeps configurations up to date.”

Options B, C, and D require custom deployments or manual IAM updates, lacking centralized automation. Therefore, Option A fully satisfies CloudOps standards for automated provisioning and ongoing management of EC2 instances across an organization.

References (AWS CloudOps Documents / Study Guide):

• AWS Certified CloudOps Engineer – Associate (SOA-C03) Exam Guide – Domain 3: Deployment, Provisioning and Automation

• AWS Systems Manager – Quick Setup and Default Host Management Configuration

• AWS Organizations Integration with Systems Manager

• AWS Well-Architected Framework – Operational Excellence Pillar