EC2 pricing models (on-demand, reserved, spot) in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding EC2 On-Demand Pricing Behavior

Which statement best describes the behavior of EC2 On-Demand instances?

A You commit to a 1-year or 3-year term and pay upfront for a discounted hourly rate.

B You pay a fixed hourly rate regardless of usage duration, with no long-term commitment.

C You bid for unused capacity and your instance can be terminated anytime AWS needs the resources.

D You pay only when your instance is actively processing requests, with automatic scaling.

💡 Hint

Think about paying for flexibility without commitment.

On-Demand instances charge a fixed hourly rate with no upfront commitment, allowing you to start and stop anytime.

❓ Architecture

intermediate

Choosing EC2 Pricing Model for a Steady Workload

You have a steady, predictable workload running 24/7 for the next 3 years. Which EC2 pricing model is most cost-effective?

A Reserved instances with a 3-year term and upfront payment.

B On-Demand instances to maintain maximum flexibility.

C Spot instances to save costs by bidding on unused capacity.

D Dedicated hosts to isolate your instances physically.

💡 Hint

Consider long-term commitment discounts.

Reserved instances offer significant discounts for steady workloads with long-term commitments.

❓ service_behavior

advanced

Spot Instance Interruption Behavior

What happens when an EC2 Spot instance is interrupted by AWS?

A AWS sends a two-minute warning before terminating the instance.

B The instance is terminated immediately without any warning.

C The instance is stopped and can be restarted later without data loss.

D The instance is paused and resumes automatically when capacity is available.

💡 Hint

Think about how AWS notifies you before reclaiming Spot capacity.

AWS provides a two-minute warning before terminating Spot instances to allow graceful shutdown.

❓ security

advanced

Security Considerations for Spot Instances

Which security risk is most relevant when using EC2 Spot instances?

A Data loss due to sudden instance termination without warning.

B Unauthorized access because Spot instances share hardware with other customers.

C Potential exposure of sensitive data if instances are reused by other customers.

D Increased attack surface due to dynamic IP addresses on Spot instances.

💡 Hint

Consider how AWS manages hardware reuse for Spot instances.

AWS wipes storage between instance uses, but hardware reuse means you must encrypt sensitive data to prevent exposure.

✅ Best Practice

expert

Optimizing Cost with Mixed EC2 Pricing Models

You want to optimize costs for a web application with variable traffic: steady baseline load and occasional spikes. Which combination of EC2 pricing models is best?

A Use Dedicated hosts for baseline and Spot instances for spikes.

B Use On-Demand instances for baseline and Reserved instances for spikes.

C Use Spot instances for baseline and On-Demand instances for spikes.

D Use Reserved instances for baseline load and Spot instances for spikes.

💡 Hint

Think about balancing cost savings and availability.

Reserved instances cover steady load cost-effectively, while Spot instances handle spikes cheaply but with possible interruptions.