Amazon EC2 is one of the most fundamental services in cloud computing and a core topic in almost every cloud or infrastructure-focused interview. Interviewers expect candidates to understand not only how EC2 instances work, but also how to choose the right instance types, pricing models, and architectural patterns for performance, cost efficiency, and availability.

This blog is designed as a complete interview questions and answers guide covering EC2 instances, spot vs on-demand pricing, Graviton processors, auto scaling, and placement groups. The explanations are simple, practical, and aligned with real-world decision-making scenarios commonly discussed in interviews.

EC2 Interview Questions and Answers

Question 1: What is Amazon EC2 and why is it widely used?

Answer: Amazon EC2 is a compute service that provides resizable virtual servers in the cloud. It allows users to run applications without managing physical hardware. EC2 is widely used because it offers flexibility in instance types, operating systems, pricing options, and scaling strategies, making it suitable for a wide range of workloads.

Question 2: What are EC2 On-Demand instances?

Answer: On-Demand instances allow users to pay for compute capacity by the second or hour without any long-term commitment. They are ideal for unpredictable workloads, short-term tasks, or applications that cannot tolerate interruptions. In interviews, they are often described as the simplest and most flexible pricing option.

Question 3: What are EC2 Spot instances?

Answer: Spot instances allow users to use spare EC2 capacity at a significantly lower cost compared to on-demand pricing. However, these instances can be interrupted when capacity is needed elsewhere. Spot instances are commonly used for fault-tolerant workloads such as batch processing, data analytics, and background jobs.

Question 4: How do you decide between Spot and On-Demand instances?

Answer: The decision depends on workload tolerance and cost requirements. On-demand instances are chosen for critical workloads that require guaranteed availability, while spot instances are suitable for workloads that can handle interruptions. Interviewers often look for candidates who can explain using a mixed strategy to balance cost and reliability.

Question 5: What are Amazon EC2 Graviton instances?

Answer: Graviton instances are powered by ARM-based processors designed to deliver better price-performance compared to traditional x86 instances. They are commonly used for web servers, containerized workloads, and microservices. Candidates should be prepared to discuss performance benefits and application compatibility considerations.

Question 6: What are the benefits of using Graviton instances?

Answer: Graviton instances offer improved performance per cost, lower power consumption, and better scalability for many workloads. In interviews, it is important to mention that applications may need to be compiled or tested for ARM compatibility before migration.

Question 7: What is EC2 Auto Scaling?

Answer: EC2 Auto Scaling automatically adjusts the number of EC2 instances based on demand. It helps maintain application availability while optimizing costs. Auto scaling ensures that applications have enough capacity during peak usage and reduces unnecessary resources during low traffic periods.

Question 8: How does Auto Scaling work?

Answer: Auto Scaling works by using scaling policies, metrics, and health checks. Based on predefined rules or observed metrics, instances are launched or terminated automatically. Interviewers often expect candidates to explain how auto scaling improves both resilience and cost efficiency.

Question 9: What are placement groups in EC2?

Answer: Placement groups influence how EC2 instances are placed within the underlying infrastructure. They are used to optimize performance, reduce latency, or improve fault tolerance depending on the placement strategy chosen.

Question 10: What are the different types of placement groups?

Answer: There are three main types of placement groups: cluster, spread, and partition. Cluster placement groups provide low-latency networking. Spread placement groups place instances on distinct hardware to reduce correlated failures. Partition placement groups distribute instances across logical partitions for large-scale workloads.

Conclusion

Amazon EC2 offers a wide range of options for building scalable, high-performance, and cost-efficient architectures. Understanding EC2 instances, spot vs on-demand pricing, Graviton processors, auto scaling, and placement groups is essential for cloud interviews. Mastery of these concepts allows candidates to make informed design decisions and confidently answer scenario-based interview questions.