Definition
Amazon EC2 (Elastic Compute Cloud) is a scalable cloud computing service provided by Amazon Web Services that allows users to launch, manage, secure, and scale virtual servers (instances) in the cloud, with flexible pricing models, storage options, networking configurations, monitoring tools, and high-availability features.
Why it matters
EC2 is the backbone of cloud infrastructure. Most web applications, APIs, DevOps pipelines, ML workloads, and enterprise systems run on EC2. Understanding EC2 means understanding how cloud computing actually works in real-world projects.
In one line
Amazon EC2 lets you run and scale virtual servers in the cloud with full control, flexibility, and pay-as-you-go pricing.
In simple words
EC2 is like renting a computer on the internet. Instead of buying physical hardware, you use AWS’s virtual computers, start them when needed, stop them anytime, increase power when traffic grows, and pay only for what you use.
For interview
Amazon EC2 is an Infrastructure-as-a-Service (IaaS) offering that provides resizable compute capacity in the AWS cloud. It supports multiple instance families, pricing models (On-Demand, Reserved, Spot, Savings Plans), storage integrations (EBS, instance store), networking components (Security Groups, NACLs, Elastic IP, Load Balancers), automation tools (Auto Scaling Groups, Launch Templates), monitoring (CloudWatch), and high-availability mechanisms across Availability Zones. Mastery of EC2 demonstrates strong cloud architecture fundamentals and hands-on AWS experience.
1. What is Amazon EC2?
Amazon EC2 (Elastic Compute Cloud) is a service that provides resizable virtual servers in the cloud. It allows you to run applications without investing in physical hardware and scale resources as needed.
2. What are EC2 instance types?
EC2 instance types define the CPU, memory, storage, and networking capacity of an instance. They are optimized for different workloads like compute-intensive, memory-intensive, or storage-heavy applications.
3. What is an AMI?
An Amazon Machine Image (AMI) is a template that contains the OS, application server, and applications. It is used to launch EC2 instances quickly with a predefined configuration.
4. What is the difference between AMI and snapshot?
An AMI is used to launch EC2 instances, while a snapshot is a backup of an EBS volume. Snapshots can be used to create new volumes, and AMIs internally use snapshots.
5. What are the pricing models of EC2?
EC2 offers On-Demand, Reserved, Spot, and Savings Plans pricing models. Each model is designed for different use cases such as short-term workloads or long-term predictable usage.
6. What is an On-Demand EC2 instance?
On-Demand instances let you pay per second or hour with no long-term commitment. They are best for unpredictable workloads or applications under development.
7. What are Reserved Instances?
Reserved Instances provide a significant discount compared to On-Demand pricing. They are suitable for steady-state workloads where usage is predictable over 1 or 3 years.
8. What are Spot Instances?
Spot Instances use unused AWS capacity and are available at lower prices. They are ideal for fault-tolerant jobs like batch processing or data analytics.
9. What happens when a Spot Instance is interrupted?
AWS provides a two-minute interruption notice before terminating the instance. Applications should be designed to save progress or gracefully shut down.
10. What is EC2 Auto Scaling?
EC2 Auto Scaling automatically adjusts the number of EC2 instances based on demand. It helps maintain performance while optimizing costs during traffic spikes or drops.
11. What is an Auto Scaling Group (ASG)?
An ASG is a collection of EC2 instances managed as a single unit. It ensures minimum, maximum, and desired numbers of instances are always running.
12. What is Elastic Load Balancer (ELB)?
ELB distributes incoming traffic across multiple EC2 instances. It improves fault tolerance and application availability.
13. Difference between ALB and NLB?
ALB operates at Layer 7 and supports path-based routing. NLB works at Layer 4 and is optimized for ultra-low latency and high throughput.
14. What is EBS?
Amazon EBS (Elastic Block Store) provides persistent block-level storage for EC2. Data remains intact even if the EC2 instance is stopped or terminated (unless deleted).
15. What are EBS volume types?
Common types include gp3, io2, st1, and sc1. Each type is optimized for different performance and cost requirements.
16. What is the difference between instance store and EBS?
Instance store provides temporary storage directly attached to the host. EBS is persistent storage that survives instance reboots and stops.
17. What is EC2 key pair?
A key pair consists of a public and private key used for secure login. It is mandatory for SSH access to Linux EC2 instances.
18. What is a security group?
A security group acts as a virtual firewall for EC2 instances. It controls inbound and outbound traffic using allow rules only.
19. Difference between security group and NACL?
Security groups are stateful and applied at the instance level. NACLs are stateless and operate at the subnet level.
20. What is a public IP in EC2?
A public IP allows an EC2 instance to communicate with the internet. It changes when the instance is stopped and started unless Elastic IP is used.
21. What is an Elastic IP?
An Elastic IP is a static public IPv4 address allocated to your AWS account. It is useful for applications that require a fixed IP address.
22. What is EC2 placement group?
Placement groups influence how EC2 instances are placed on underlying hardware. They help optimize for latency, throughput, or fault tolerance.
23. Types of placement groups?
Cluster, Spread, and Partition placement groups are available. Each serves different high availability and performance needs.
24. What is user data in EC2?
User data allows scripts to run automatically at instance launch. It is commonly used to install software or configure services.
25. What is EC2 metadata?
Metadata provides information about the running instance. It can be accessed from within the instance and used for automation.
26. What is a launch template?
A launch template defines instance configuration parameters. It simplifies instance launches and is required for Auto Scaling.
27. Difference between launch configuration and launch template?
Launch configurations are legacy and immutable. Launch templates support versioning and more advanced features.
28. What is EC2 hibernation?
Hibernation saves the RAM state to EBS before stopping the instance. It allows faster resume without reinitializing applications.
29. What is EC2 Nitro System?
The Nitro System offloads virtualization functions to dedicated hardware. It improves performance, security, and scalability.
30. How do you monitor EC2 instances?
Amazon CloudWatch is used to monitor EC2 metrics. It provides CPU, disk, network usage, and custom metrics.
31. What is detailed monitoring?
Detailed monitoring provides metrics at 1-minute intervals. Basic monitoring provides metrics every 5 minutes.
32. How do you secure EC2 instances?
Use IAM roles, security groups, and encryption. Regular patching and monitoring also enhance security.
33. What is IAM role for EC2?
An IAM role allows EC2 to access AWS services securely. It avoids storing credentials inside the instance.
34. How do you reduce EC2 costs?
Use Reserved or Spot Instances where possible. Enable Auto Scaling and right-size instances regularly.
35. What is EC2 right-sizing?
Right-sizing involves selecting appropriate instance types. It avoids over-provisioning and reduces costs.
36. What is termination protection?
Termination protection prevents accidental deletion of instances. It must be disabled before terminating an instance.
37. What happens when an EC2 instance is stopped?
The instance shuts down but EBS data remains. Public IP is released unless Elastic IP is attached.
38. What happens when an EC2 instance is terminated?
The instance is permanently deleted. Data on instance store volumes is lost.
39. Can you change instance type?
Yes, but the instance must be stopped first. This helps scale resources based on demand.
40. What is enhanced networking?
Enhanced networking improves packet per second performance. It reduces latency and jitter for high-performance applications.
41. What is EC2 capacity reservation?
It reserves compute capacity in a specific AZ. Useful for mission-critical workloads with guaranteed availability.
42. How does EC2 support high availability?
By using multiple AZs and Auto Scaling Groups. Load balancers distribute traffic across instances.
43. What is a bastion host?
A bastion host is a secure gateway instance. It allows controlled access to private instances.
44. What is blue-green deployment using EC2?
Two environments (blue and green) are maintained. Traffic is switched to the new version with minimal downtime.
45. What is EC2 warm pool?
Warm pools keep pre-initialized instances ready. They reduce scaling time during sudden traffic spikes.
46. What is EC2 serial console?
It allows troubleshooting of unresponsive instances. Useful when SSH access is unavailable.
47. What is EC2 fleet?
EC2 Fleet launches multiple instance types at once. It optimizes cost and availability across instance options.
48. Can EC2 be used for container workloads?
Yes, EC2 is commonly used with ECS or EKS. It provides full control over the underlying infrastructure.
49. What is the use case of EC2 in real life?
Hosting web applications, APIs, and backend services. Also used for ML training, batch processing, and enterprise apps.
50. Why do interviewers focus heavily on EC2?
EC2 is the foundation of AWS compute services. Understanding EC2 shows strong cloud fundamentals and real-world experience.
Conclusion.
Amazon EC2 is one of the most critical services in AWS, and a strong understanding of it is essential for clearing cloud interviews. From instance types and pricing models to security, scaling, and real-world deployment scenarios, EC2 concepts test both theoretical knowledge and hands-on experience.
By mastering these 50 EC2 interview questions and answers, you not only prepare yourself for common interview discussions but also build the confidence to design, operate, and optimize real-world cloud solutions. Whether you are a fresher, a DevOps engineer, or a solutions architect, deep EC2 knowledge forms the foundation for success in AWS-focused roles.
Consistent practice, practical exposure, and understanding why each service is used will help you stand out in interviews and perform effectively on the job. Keep exploring, keep experimenting, and treat EC2 not just as a service but as a core building block of cloud architecture.
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