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Zorluk: OrtaImplementing Auto Scaling and Fault Tolerance

A digital payment processing company operates a backend microservice on Amazon EC2 instances within an Auto Scaling Group (ASG) behind an Application Load Balancer (ALB). The instances retrieve tasks from an internal processing queue and verify external merchant accounts by calling external APIs. The instances are situated in private subnets across three Availability Zones (AZs), with all outbound internet traffic routed through a single NAT Gateway located in the first AZ. During a major promotional campaign, the application experiences a massive, instantaneous surge in requests. This causes a sudden latency spike on the ALB, leading to dropped connections. Simultaneously, the ASG attempts to scale out rapidly, but because instances run custom bootstrapping scripts to download updates that take 8 minutes to complete, the ASG repeatedly launches additional instances before the first batch is fully operational. Shortly after, a physical fiber outage disables the first AZ, which causes transaction processing to stall entirely for instances in the remaining two active AZs. Which set of actions will resolve the availability, scaling latency, and initialization issues?

  1. A
    Request ALB pre-warming from AWS Support prior to the promotional campaign, keep outbound traffic routed through the existing single NAT Gateway to optimize resource costs, bake application dependencies into a golden Amazon Machine Image (AMI) to bypass runtime bootstrapping, and adjust the ASG's scaling policies to use a warm-up period that matches the new launch duration.
  2. B
    Request ALB pre-warming from AWS Support prior to the promotional campaign, provision dedicated NAT gateways across all three active zones and update private subnet routing to use zone-specific gateways, and configure the ASG's scaling policies with a warm-up period that is shorter than the 8-minute bootstrapping time of the instances while continuing to run the scripts at startup.
  3. Request ALB pre-warming from AWS Support prior to the promotional campaign, provision dedicated NAT gateways across all three active zones and update private subnet routing to use zone-specific gateways, bake application dependencies into a golden Amazon Machine Image (AMI) to bypass runtime bootstrapping, and adjust the ASG's scaling policies to use a warm-up period that matches the new launch duration.Cevap
  4. D
    Rely on the ALB's default scaling behavior to handle the promotional campaign traffic, provision dedicated NAT gateways across all three active zones and update private subnet routing to use zone-specific gateways, bake application dependencies into a golden Amazon Machine Image (AMI) to bypass runtime bootstrapping, and adjust the ASG's scaling policies to use a warm-up period that matches the new launch duration.

Cevap

Request ALB pre-warming from AWS Support prior to the promotional campaign, provision dedicated NAT gateways across all three active zones and update private subnet routing to use zone-specific gateways, bake application dependencies into a golden Amazon Machine Image (AMI) to bypass runtime bootstrapping, and adjust the ASG's scaling policies to use a warm-up period that matches the new launch duration.
The correct solution addresses all three failure modes described in the scenario. Deploying a NAT Gateway in each active Availability Zone ensures that a zone outage does not disrupt outbound internet connectivity for the instances in the surviving zones. Creating a custom golden AMI containing all application dependencies removes the 8-minute bootstrap latency, reducing instance startup times. Configuring the warm-up period to match this shortened startup duration prevents the Auto Scaling Group from launching unnecessary redundant instances. Lastly, requesting Application Load Balancer pre-warming prepares the load balancer to instantly support the sudden traffic surge without dropping client connections.

Adım Adım Çözüm

1
Deploy independent NAT Gateways in each of the three Availability Zones and configure each private subnet's route tables accordingly.
Fault isolation is achieved for outbound internet traffic; the failure of a single Availability Zone does not impact external API connectivity for the remaining healthy zones.
Using a single NAT Gateway creates a single point of failure (SPOF) for the entire VPC's outbound traffic.
2
Bake all dependencies, runtime engines, and updates directly into a custom Amazon Machine Image (AMI) rather than performing bootstrapping tasks during instance initialization.
The instance boot time is significantly reduced, allowing instances to reach a healthy state in under a minute.
Lengthy bootstrap scripts run on instance launch delay scale-out actions, causing metrics to remain elevated and forcing the ASG to launch redundant instances.
3
Configure the ASG's scaling policies and instance warm-up periods to reflect the rapid startup time of the new golden AMI.
The ASG correctly waits for newly launched instances to become active before triggering subsequent scaling actions, preventing over-scaling.
The scaling warm-up period must be at least as long as the time it takes for an instance to start passing health checks and handling workload traffic.
4
Submit a request to AWS Support for Application Load Balancer pre-warming before the promotional campaign begins.
The ALB is pre-configured with sufficient internal resource capacity to handle the immediate influx of connections without experiencing processing bottlenecks.
ALBs scale automatically but require time to handle sudden, severe traffic spikes. Pre-warming prevents connection drops at the start of the event.

Anahtar Kavram

Auto Scaling Group scaling behavior optimization and VPC outbound path fault tolerance
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Implementing Auto Scaling and Fault Tolerance