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Zorluk: OrtaImplementing Auto Scaling and Fault Tolerance

An enterprise hosts a legacy document processing application on Amazon EC2 instances in an Auto Scaling group (ASG) behind an Application Load Balancer (ALB). The instances reside in private subnets across two Availability Zones, AZ-A and AZ-B. Outbound internet traffic from both private subnets is routed through a single NAT Gateway located in the public subnet of AZ-A to allow instances to download critical libraries during startup.

The application instances require approximately 420420 seconds to complete bootstrapping, start services, and pass ALB health checks. The ASG is currently configured with a simple scaling policy based on CPU utilization and has a default cooldown of 300300 seconds.

During sudden traffic surges, the ASG launches excessive redundant instances, resulting in database connection exhaustion. Additionally, a recent outage in AZ-A caused the instances launching in AZ-B to fail bootstrapping, resulting in application downtime.

Which combination of actions should a solutions architect take to resolve the scaling and fault tolerance issues?

  1. Configure a target tracking scaling policy with an estimated instance warmup of 450450 seconds. Deploy a second NAT Gateway in the public subnet of AZ-B, and update the route table for the private subnets in AZ-B to route outbound internet traffic through the new NAT Gateway.Cevap
  2. B
    Configure a simple scaling policy with a decreased default cooldown period of 180180 seconds. Deploy a second NAT Gateway in the public subnet of AZ-B, and update the route table for the private subnets in AZ-B to route outbound internet traffic through the new NAT Gateway.
  3. C
    Configure a target tracking scaling policy with an estimated instance warmup of 450450 seconds. Maintain the single NAT Gateway in AZ-A to minimize operational costs, and increase the Application Load Balancer health check grace period to 500500 seconds.
  4. D
    Submit a request to AWS Support to pre-warm the Application Load Balancer to absorb the traffic surges. Retain the simple scaling policy with the 300300-second default cooldown, and enable cross-zone load balancing on the Application Load Balancer to route traffic to AZ-B without deploying an additional NAT Gateway.

Cevap

Configure a target tracking scaling policy with an estimated instance warmup of 450450 seconds. Deploy a second NAT Gateway in the public subnet of AZ-B, and update the route table for the private subnets in AZ-B to route outbound internet traffic through the new NAT Gateway.
The correct option addresses both the scaling delay and network fault tolerance. Configuring a target tracking scaling policy with an estimated instance warmup of 450450 seconds ensures the Auto Scaling group does not launch additional instances while existing ones are still bootstrapping (since 450450 seconds covers the 420420-second startup delay). Deploying a dedicated NAT Gateway in AZ-B ensures that instances in AZ-B retain internet access for library downloads if AZ-A undergoes an outage.

Adım Adım Çözüm

1
Evaluate the bootstrapping timeline against scaling thresholds.
Identify that the current 300300-second cooldown is shorter than the 420420-second instance launch time, causing premature additional scale-out actions.
Aligning scaling evaluation intervals or warmup periods with actual instance readiness prevents over-provisioning.
2
Address the single point of failure in network routing.
Deploy a second NAT Gateway in AZ-B and configure the private route tables locally.
This guarantees that instances in AZ-B can still download required dependencies and bootstrap successfully even if AZ-A goes down.

Anahtar Kavram

Auto Scaling Warmup and Multi-AZ Redundancy
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Implementing Auto Scaling and Fault Tolerance