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Zorluk: OrtaImplementing Auto Scaling and Fault Tolerance

A retail company operates a mobile shopping application. The application's backend is hosted on Amazon EC2 instances in an Auto Scaling group (ASG) across three Availability Zones. Outbound API calls to external payment gateways are routed from private subnets through a single NAT Gateway located in one public subnet. During a simulated flash sale, traffic increases from 200200 to 80,00080,000 requests per minute in less than 22 minutes. During testing, the Availability Zone containing the NAT Gateway experienced a simulated outage, which disrupted all external payment processing. Additionally, the EC2 instances require 88 minutes to complete bootstrapping and application initialization, but the ASG's cooldown period is set to 300300 seconds, causing the ASG to launch redundant instances before the previously launched instances can begin serving traffic and reduce metric load. Which combination of actions should the solutions architect take to resolve these scaling and reliability issues with the lowest operational overhead?

  1. Provision a NAT Gateway in each of the three Availability Zones and update the route tables for each private subnet to point to the local NAT Gateway. Increase the Auto Scaling group scaling cooldown period to 600600 seconds to exceed the instance initialization time. Request AWS Support to pre-warm the Application Load Balancer prior to the scheduled flash sale.Cevap
  2. B
    Provision a NAT Gateway in each of the three Availability Zones and update the route tables for each private subnet to point to the local NAT Gateway. Retain the Auto Scaling group scaling cooldown period at 300300 seconds, but switch the scaling policy to target tracking based on average CPU utilization. Request AWS Support to pre-warm the Application Load Balancer prior to the scheduled flash sale.
  3. C
    Maintain a single NAT Gateway in one public subnet but configure a Route 53 active-passive DNS failover record pointing to a secondary NAT Gateway in another Availability Zone. Increase the Auto Scaling group scaling cooldown period to 600600 seconds. Request AWS Support to pre-warm the Application Load Balancer prior to the scheduled flash sale.
  4. D
    Provision a NAT Gateway in each of the three Availability Zones and update the route tables for each private subnet to point to the local NAT Gateway. Increase the Auto Scaling group scaling cooldown period to 600600 seconds. Rely on the Application Load Balancer's native automatic scaling to handle the instant flash sale traffic spike without requesting pre-warming.

Cevap

Provision a NAT Gateway in each of the three Availability Zones and update the route tables for each private subnet to point to the local NAT Gateway. Increase the Auto Scaling group scaling cooldown period to 600600 seconds to exceed the instance initialization time. Request AWS Support to pre-warm the Application Load Balancer prior to the scheduled flash sale.
The correct solution resolves the single point of failure by establishing localized NAT Gateways in each Availability Zone. It addresses the over-scaling issue by setting a cooldown period (600600 seconds) that exceeds the 88-minute (480480-second) bootstrap time, ensuring the ASG waits long enough for new instances to start handling load. Finally, it prevents ALB bottlenecks during the sharp traffic surge by requesting pre-warming from AWS Support.

Adım Adım Çözüm

1
Deploy a NAT Gateway in each Availability Zone and associate them with the respective private subnets' route tables.
This establishes redundant, localized outbound paths, eliminating the single point of failure for internet-facing payment calls.
Outbound traffic from a private subnet to the internet is governed by local VPC route tables, not DNS. Redundant NAT Gateways across AZs ensure fault tolerance.
2
Increase the Auto Scaling group scaling cooldown period from 300300 seconds to 600600 seconds.
The cooldown period now exceeds the 88-minute (480480 seconds) bootstrapping and initialization time.
A cooldown period longer than the initialization time prevents the group from scaling out prematurely and launching unnecessary instances before previous ones can process load.
3
Contact AWS Support to pre-warm the Application Load Balancer prior to the flash sale.
The ALB is provisioned with sufficient capacity upfront to handle the sudden surge in traffic.
An instantaneous increase from 200200 to 80,00080,000 requests per minute is too rapid for the Application Load Balancer's default scaling response, making pre-warming essential to prevent service denial.

Anahtar Kavram

Ensuring fault tolerance and scalable performance by configuring multi-AZ NAT Gateways, matching Auto Scaling cooldowns to instance bootstrap times, and pre-warming Application Load Balancers for flash traffic.
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Implementing Auto Scaling and Fault Tolerance