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Zorluk: ZorImplementing Auto Scaling and Fault Tolerance

A media company hosts a high-throughput video transcoding platform on Amazon EC2 instances in an Auto Scaling Group (ASG) behind an Application Load Balancer (ALB). The EC2 instances reside in private subnets across three Availability Zones. During video upload surges, the system encounters two critical issues: first, newly launched EC2 instances require 88 minutes to download dependencies and complete their bootstrapping sequence, while the scaling policy cooldown is set to 33 minutes, resulting in rapid, unnecessary scale-out (thrashing) of instances. Second, when the single NAT Gateway deployed in Availability Zone A experiences network degradation, transcoding instances in all three Availability Zones fail to access the internet to retrieve dependencies, halting the processing pipeline. Which of the following combinations of actions will resolve these issues? (Select TWO.)

  1. Deploy a dedicated NAT Gateway in each Availability Zone where the EC2 instances reside, and update the route tables of the private subnets to direct outbound traffic (0.0.0.0/00.0.0.0/0) to the respective local NAT Gateway.Cevap
  2. Update the Auto Scaling group launch template to use a pre-baked AMI containing the transcoding dependencies, and set the default cooldown and instance warmup periods to exceed the remaining bootstrapping time.Cevap
  3. C
    Consolidate all outbound internet routing by deploying a single high-bandwidth NAT Gateway in a shared services VPC and routing private subnet traffic to it over an AWS Transit Gateway.
  4. D
    Configure the Auto Scaling group cooldown period to 6060 seconds to ensure that the target tracking scaling policy immediately triggers subsequent scale-out actions to handle transcoding load surges.
  5. E
    Submit an AWS Support request to enable pre-warming for the Application Load Balancer to ensure it automatically bypasses the bootstrapping sequence during rapid instance scale-out events.

Cevap

The correct actions are to deploy a dedicated NAT Gateway in each Availability Zone where the EC2 instances reside, update the private subnet route tables to direct traffic to their local NAT Gateways, update the launch template to use a pre-baked AMI with transcoding dependencies, and ensure the scaling policy cooldown and warmup periods exceed the remaining initialization time.
Deploying a NAT Gateway in each Availability Zone ensures that a local zone failure does not break the outbound connectivity of instances in other zones. Implementing a pre-baked AMI and configuring scaling warmup/cooldown parameters to exceed the bootstrap time stops the Auto Scaling group from spawning unnecessary instances (thrashing) before the newly launched instances are ready to assume load.

Adım Adım Çözüm

1
Analyze the fault-tolerance issue related to internet egress.
The single NAT Gateway in Availability Zone A represents a single point of failure.
If the single NAT Gateway degrades, all instances in all zones lose internet access. Deploying a NAT Gateway in each zone and mapping subnets to their respective local gateway eliminates this risk.
2
Analyze the auto-scaling thrashing issue.
The boot time (88 minutes) is much longer than the cooldown period (33 minutes).
Because the scaling policy does not wait long enough for new instances to start processing traffic, it continues to scale out unnecessarily. Pre-baking dependencies into the AMI and adjusting the cooldown/warmup parameters resolves this.

Anahtar Kavram

Auto Scaling cooldown configuration and Multi-AZ NAT Gateway redundancy
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Implementing Auto Scaling and Fault Tolerance