An online auction platform experiences sudden, massive surges in traffic during the final … — AWS Certified Solutions Architect - Professional

An online auction platform experiences sudden, massive surges in traffic during the final minutes of high-value auctions. The application runs on Amazon EC2 instances in an Auto Scaling group (ASG) behind an Application Load Balancer (ALB). The instances use a custom launch template that takes $5\text{ minutes}$ ( $300\text{ seconds}$ ) to download application libraries and start the service. Outbound API calls to external payment gateways are routed through a single NAT Gateway in Availability Zone $\text{us-east-1a}$ . During auction finales, the ALB immediately returns $503\text{ Service Unavailable}$ errors to new requests. Additionally, the ASG launches far more instances than needed during a surge because the scaling policy triggers additional instances before the first batch is fully functional. Which combination of actions will resolve these scaling and fault-tolerance issues with the lowest operational overhead?

A
Configure an Amazon CloudFront distribution in front of the ALB to cache all dynamic auction bids, reduce the ASG cooldown period to $60\text{ seconds}$ , and maintain the single NAT Gateway in $\text{us-east-1a}$ to control costs.
B
Configure a target tracking scaling policy based on average CPU utilization, set the ASG cooldown period to $120\text{ seconds}$ , and configure Amazon Route 53 to distribute outbound traffic across multiple NAT Instances deployed in the private subnets.
Request AWS Support to pre-warm the ALB before scheduled high-value auctions, configure the ASG scaling policy's instance warmup to $350\text{ seconds}$ , and deploy a NAT Gateway in each Availability Zone with corresponding route table updates.Answer
D
Deploy a Network Load Balancer (NLB) in front of the ALB to handle the traffic spikes without pre-warming, set the ASG default cooldown to $180\text{ seconds}$ , and associate the existing NAT Gateway with multiple private route tables across all Availability Zones.

Answer

Requesting AWS Support to pre-warm the ALB, setting the ASG warmup period to

350\text{ seconds}

, and deploying a NAT Gateway in each Availability Zone.

To resolve immediate

503

errors from flash traffic, the ALB must be pre-warmed since dynamic scaling of the load balancer is not instantaneous. To prevent over-provisioning during scaling, the instance warmup period must be configured to be longer than the boot and configuration time of the instances (

300\text{ seconds}

), making

350\text{ seconds}

appropriate. For fault tolerance, a NAT Gateway must be deployed in each Availability Zone to ensure outbound traffic is not dependent on a single zone.

Step-by-Step Solution

Address the load balancer bottleneck during sudden, large-scale traffic spikes.

The Application Load Balancer (ALB) is configured with pre-warming requested from AWS Support before scheduled auctions.

Dynamic scaling of the ALB is too slow for instantaneous spikes, leading to

503

errors. Pre-warming prepares the ALB with adequate capacity.

Configure the Auto Scaling Group (ASG) to prevent over-provisioning during scaling events.

The instance warmup is set to

350\text{ seconds}

, which is greater than the

300\text{ seconds}

bootstrap time.

This prevents the ASG from launching additional instances before the previously launched ones have finished bootstrapping and started reporting metrics.

Design a fault-tolerant outbound NAT architecture.

Deploy a NAT Gateway in each Availability Zone where the EC2 instances are located, and update local route tables accordingly.

Having a NAT Gateway per AZ ensures that a failure in one Availability Zone does not impact outbound connectivity for resources in other zones.

Key Concept

ELB pre-warming, Auto Scaling Group warmup tuning, and multi-AZ NAT Gateway redundancy.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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