A logistics company runs a fleet tracking application on Amazon EC2 instances in an Auto S… — AWS Certified Solutions Architect - Professional

A logistics company runs a fleet tracking application on Amazon EC2 instances in an Auto Scaling group (ASG) behind an Application Load Balancer (ALB). The instances run in private subnets and send route telemetry updates to an external third-party API via a single NAT Gateway located in Availability Zone A.

Every day at $08:00\text{ UTC}$ , the application experiences a massive surge in traffic, spiking from $500\text{ requests per second}$ to $30,000\text{ requests per second}$ within $2\text{ minutes}$ . During this peak, users experience HTTP 503 Service Unavailable errors and data ingestion failures for the first $10\text{ to }15\text{ minutes}$ .

An architectural review reveals the following:
* The EC2 instances require $8\text{ minutes}$ to download configuration files, initialize application services, and pass load balancer health checks.
* The ASG uses a target tracking scaling policy based on Average CPU Utilization with a default cooldown of $300\text{ seconds}$ .
* During the surge, the ASG continuously launches new instances before the previously launched instances are fully initialized and ready to receive traffic.
* A recent outage in Availability Zone A halted all outbound telemetry transmissions for the entire application, despite instances in other zones remaining healthy.

The company wants to improve the fault tolerance and auto-scaling responsiveness of the architecture. Which combination of actions should the Solutions Architect implement to resolve these issues? (Select TWO.)

Configure a scheduled scaling policy to scale out the Auto Scaling group in advance of the daily peak, and update the dynamic scaling policy to use an estimated instance warmup of $540\text{ seconds}$ .Answer
Deploy a NAT Gateway in each Availability Zone, and update the route tables of the private subnets to direct outbound traffic to the NAT Gateway in the same Availability Zone.Answer
C
Decrease the default cooldown period of the Auto Scaling group to $180\text{ seconds}$ to allow the group to launch new instances more rapidly during the traffic surge.
D
Configure a single secondary NAT Gateway in Availability Zone B, and configure Route 53 failover routing to direct outbound traffic to the secondary gateway if the primary NAT Gateway becomes unhealthy.
E
Rely on the Application Load Balancer's automatic scaling to absorb the rapid daily spike, and configure target tracking scaling based on Average CPU Utilization with a target of $20\%$ to initiate earlier scaling.

Answer

Configure a scheduled scaling policy to scale out the Auto Scaling group in advance of the daily peak, update the dynamic scaling policy to use an estimated instance warmup of

540\text{ seconds}

, deploy a NAT Gateway in each Availability Zone, and update the route tables of the private subnets to direct outbound traffic to the local NAT Gateway.

The correct architecture uses scheduled scaling to pre-provision instances before the predictable daily spike at

08:00\text{ UTC}

starts, and sets the estimated instance warmup to

540\text{ seconds}

to prevent dynamic target tracking from launching extra instances while existing ones are still bootstrapping (which takes

8\text{ minutes}

). It also deploys a NAT Gateway in each Availability Zone to ensure high availability for outbound traffic, preventing an outage in a single zone from affecting the entire architecture.

Step-by-Step Solution

Analyze the scaling behavior and identify the bottleneck caused by the

8\text{-minute}

bootstrap time versus the

300\text{-second}

default cooldown.

Determine that the estimated instance warmup for dynamic scaling must be increased to at least

480\text{ seconds}

(specifically

540\text{ seconds}

) to prevent the Auto Scaling group from launching redundant instances prematurely.

This prevents scaling policy thrashing during rapid traffic spikes.

Address the predictable daily spike occurring at

08:00\text{ UTC}

Implement scheduled scaling to launch instances before the traffic surge begins.

Scheduled scaling ensures capacity is pre-provisioned, avoiding the latency associated with reactive dynamic scaling and load balancer delays.

Resolve the single point of failure for outbound traffic routed through Availability Zone A.

Deploy a NAT Gateway in each Availability Zone and associate them with corresponding subnet route tables.

This establishes multi-AZ redundancy, ensuring outbound traffic remains operational if one zone goes offline.

Key Concept

Mitigating scaling policy thrashing through estimated instance warmup tuning, pre-provisioning capacity for predictable spikes, and achieving multi-AZ fault tolerance for outbound network paths.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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