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Answer: Provision a subnet in each Availability Zone. Configure the Auto Scaling group to distribute the EC2 instances across both Availability Zones. Configure the DB instance for Multi-AZ deployment.
## Explanation **Correct Answer: C** **Why Option C is correct:** 1. **Provision a subnet in each Availability Zone**: This is the correct approach because subnets cannot span multiple Availability Zones. Each subnet must be contained within a single Availability Zone. 2. **Configure the Auto Scaling group to distribute EC2 instances across both Availability Zones**: Auto Scaling groups can be configured to launch instances across multiple Availability Zones, which provides high availability for the compute layer. 3. **Configure the DB instance for Multi-AZ deployment**: Amazon RDS Multi-AZ deployment automatically creates a standby replica in a different Availability Zone. This provides automatic failover capability and high availability for the database layer. **Why other options are incorrect:** - **Option A**: Incorrect because "Configure the DB instance with connections to each network" doesn't provide high availability. Simply having network connections doesn't create a standby replica or automatic failover. - **Option B**: Incorrect because "Provision two subnets that extend across both Availability Zones" is not possible. Subnets cannot span multiple Availability Zones in AWS. - **Option D**: Incorrect because "Provision a subnet that extends across both Availability Zones" is not possible. Subnets are confined to a single Availability Zone. **Key AWS Concepts:** - **Subnets**: Cannot span multiple Availability Zones. Each subnet exists within a single Availability Zone. - **Auto Scaling Groups**: Can be configured to launch instances across multiple Availability Zones for high availability. - **RDS Multi-AZ**: Creates a synchronous standby replica in a different Availability Zone with automatic failover capability. - **High Availability**: Requires redundancy at multiple layers - compute (EC2 across AZs), database (RDS Multi-AZ), and networking (subnets in each AZ).
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A company is running a critical business application on Amazon EC2 instances behind an Application Load Balancer. The EC2 instances run in an Auto Scaling group and access an Amazon RDS DB instance.
The design did not pass an operational review because the EC2 instances and the DB instance are all located in a single Availability Zone. A solutions architect must update the design to use a second Availability Zone.
Which solution will make the application highly available?
A
Provision a subnet in each Availability Zone. Configure the Auto Scaling group to distribute the EC2 instances across both Availability Zones. Configure the DB instance with connections to each network.
B
Provision two subnets that extend across both Availability Zones. Configure the Auto Scaling group to distribute the EC2 instances across both Availability Zones. Configure the DB instance with connections to each network.
C
Provision a subnet in each Availability Zone. Configure the Auto Scaling group to distribute the EC2 instances across both Availability Zones. Configure the DB instance for Multi-AZ deployment.
D
Provision a subnet that extends across both Availability Zones. Configure the Auto Scaling group to distribute the EC2 instances across both Availability Zones. Configure the DB instance for Multi-AZ deployment.