Explanation: C is correct because turning on multi-factor authentication (MFA) for added security during the login process is one of the IAM security best practices recommended by AWS. MFA adds an extra layer of protection on top of the user name and password, making it harder for attackers to access the AWS account. A is incorrect because using the account root user access keys for administrative tasks is not a good practice, as the root user has full access to all the resources in the AWS account and can cause irreparable damage if compromised. AWS recommends creating individual IAM users with the least privilege principle and using roles for applications that run on Amazon EC2 instances. B is incorrect because granting broad permissions so that all company employees can access the resources they need is not a good practice, as it increases the risk of unauthorized or accidental actions on the AWS resources. AWS recommends granting only the permissions that are required to perform a task and using groups to assign permissions to IAM users. D is incorrect because avoiding rotating credentials to prevent issues in production applications is not a good practice, as it increases the risk of credential leakage or compromise. AWS recommends rotating credentials regularly and using temporary security credentials from AWS STS when possible.

Explanation: The Envision phase of the cloud transformation journey is where the company defines its vision, business drivers, and desired outcomes for the cloud adoption. The company also identifies its capability gaps by using the AWS Cloud Adoption Framework (AWS CAF) perspectives, which are business, people, governance, platform, security, and operations2.

Explanation: The most cost-effective EC2 instance purchasing option for the company that needs to host a web server on Amazon EC2 instances for at least 1 year and cannot tolerate interruption is Partial Upfront Reserved Instances. Reserved Instances are a pricing model that offer significant discounts compared to On-Demand Instances in exchange for a commitment to use a specific amount of compute capacity for a fixed period of time (1 or 3 years). Partial Upfront Reserved Instances require customers to pay a portion of the total cost upfront, and the remaining cost in monthly installments over the term. This option offers a lower effective hourly rate than No Upfront Reserved Instances, which require no upfront payment but have higher monthly payments. On-Demand Instances and Spot Instances are not the best options for the company. On-Demand Instances are a pricing model that offer the most flexibility and no long-term commitment, but have the highest hourly rate. Spot Instances are a pricing model that offer the lowest cost, but are subject to interruption based on supply and demand.

Explanation: AWS Config is a service that enables you to assess, audit, and evaluate the configurations of your AWS resources. AWS Config continuously monitors and records your AWS resource configurations and allows you to automate the evaluation of recorded configurations against desired configurations. AWS Config can help you determine when an EBS volume was removed from an EC2 instance by providing a timeline of configuration changes and compliance status. AWS Trusted Advisor, Amazon Timestream, and Amazon QuickSight do not provide the same level of configuration tracking and auditing as AWS Config.

Explanation: AWS Auto Scaling is the AWS service that allows users to optimize the number of EC2 instances based on the usage pattern, as it automatically adjusts the capacity to maintain steady and predictable performance at the lowest possible cost. Spot Instances are a way to reduce the cost of EC2 instances by bidding on unused EC2 capacity, but they are not suitable for applications that require steady and reliable performance. Reserved Instances are a way to reduce the cost of EC2 instances by committing to a certain amount of usage for a period of time, but they are not flexible to adjust to the usage pattern. AWS CloudFormation is a way to automate the creation and management of AWS resources, but it does not optimize the number of EC2 instances based on the usage pattern. These concepts are explained in the AWS Cloud Practitioner Essentials course3.

Explanation: Amazon ElastiCache is a service that offers fully managed in-memory data store and cache services that deliver sub-millisecond response times to applications. You can use Amazon ElastiCache to improve the performance of your applications by retrieving data from fast, managed, in-memory data stores, instead of relying entirely on slower diskbased databases. Amazon Aurora is a relational database service that combines the performance and availability of high-end commercial databases with the simplicity and cost-effectiveness of open source databases. Amazon RDS is a service that makes it easy to set up, operate, and scale a relational database in the cloud. Amazon DynamoDB is a key-value and document database that delivers single-digit millisecond performance at any scale. None of these services are in-memory data store services.

Explanation: Create annotated documentation is the design principle that is included in the operational excellence pillar of the AWS Well-Architected Framework. According to the AWS Well-Architected Framework whitepaper, creating annotated documentation means "documenting your workload so that the team understands the architecture, how to operate the workload, and how the workload delivers value to customers."3 Anticipate failure, ensure performance efficiency, and optimize costs are design principles that belong to other pillars of the AWS Well-Architected Framework, such as reliability, performance efficiency, and cost optimization.

Explanation: Amazon Virtual Private Cloud (Amazon VPC) is the AWS service that allows customers to create multiple isolated networks in the same AWS account. A VPC is a logically isolated section of the AWS Cloud where customers can launch AWS resources in a virtual network that they define. Customers can create multiple VPCs within an AWS account, each with its own IP address range, subnets, route tables, security groups, network access control lists, gateways, and other components. AWS Transit Gateway, Internet gateway, and Amazon EC2 are not services or components that provide the functionality of creating multiple isolated networks in the same AWS account. AWS Transit Gateway is a service that enables customers to connect their Amazon VPCs and their on-premises networks to a single gateway. An Internet gateway is a component that enables communication between instances in a VPC and the Internet. Amazon EC2 is a service that provides scalable compute capacity in the cloud34.

Explanation: Decoupling the components of an application means reducing the dependencies and interactions between them, which can improve the application’s reliability, scalability, and performance. Decoupling can be achieved by using services such as Amazon Simple Queue Service (Amazon SQS), Amazon Simple Notification Service (Amazon SNS), and AWS Lambda1

Explanation: Deploying the application in multiple Availability Zones is the best way to ensure high availability for the application. Availability Zones are isolated locations within an AWS Region that are engineered to be fault-tolerant from failures in other Availability Zones. By deploying the application in multiple Availability Zones, the company can reduce the impact of outages and increase the resilience of the application. Deploying the application in a single Availability Zone, on AWS Direct Connect, or on Reserved Instances does not provide the same level of high availability as deploying the application in multiple Availability Zones. Source: Availability Zones

Explanation: According to the AWS shared responsibility model, AWS is responsible for the security of the cloud, while the customer is responsible for the security in the cloud. This means that AWS provides the physical and environmental controls, the service and communications protection, and the awareness and training for its employees, while the customer provides the patch and configuration management, the identity and access management, the data encryption, and the firewall configuration for its resources3.

Explanation: The benefit of the AWS Cloud that helps companies achieve lower usage costs because of the aggregate usage of all AWS users is economies of scale. Economies of scale means that AWS can achieve lower costs and higher efficiency by operating at a massive scale and passing the savings to the customers. AWS leverages the aggregate usage of all AWS users to negotiate better prices with hardware vendors, optimize power consumption, and improve operational processes. As a result, AWS can offer lower and more flexible pricing options to the customers, such as pay-as-you-go, reserved, and spot pricing models. No need to guess capacity, ability to go global in minutes, and increased speed and agility are other benefits of the AWS Cloud, but they are not directly related to the aggregate usage of all AWS users. No need to guess capacity means that AWS customers can avoid the risk of over-provisioning or under-provisioning resources, and scale up or down as needed. Ability to go global in minutes means that AWS customers can deploy their applications and data in multiple regions around the world, and deliver them to users with high performance and availability. Increased speed and agility means that AWS customers can quickly and easily provision and access AWS resources, and accelerate their innovation and time to market.