Amazon EC2 (Elastic Compute Cloud) Interview Questions and Answers

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Amazon EC2 (Elastic Compute Cloud)

Amazon EC2 Overview
Amazon Elastic Compute Cloud (EC2) is a core component of Amazon Web Services (AWS), providing scalable and resizable compute capacity in the cloud. It enables users to rent virtual servers to run their applications, offering a secure, flexible, and reliable computing environment. Designed to simplify web-scale computing for developers, Amazon EC2 provides a user-friendly web service interface for obtaining and configuring virtual machines with minimal effort. Users have full control over their computing resources and can leverage Amazon’s robust infrastructure.

Q: What is Amazon EC2?

Amazon EC2 is a web service that delivers resizable compute capacity in the cloud. Its purpose is to simplify cloud computing at scale, offering developers an intuitive interface to manage resources efficiently. It allows users to launch virtual servers in Amazon’s trusted computing environment with full control over configuration and operation.

Q: Can you explain the different types of instances available in EC2?

Amazon EC2 offers a wide range of instance types to suit diverse use cases. Each instance type provides different combinations of CPU, memory, storage, and networking resources, enabling users to choose the best fit for their applications. The primary categories are:

• General Purpose: Balanced resources for diverse workloads, ideal for web servers and development environments.
• Compute Optimized: High-performance processors for compute-intensive applications such as batch processing and high-performance computing (HPC).
• Memory Optimized: Enhanced memory capacity for workloads requiring large in-memory datasets, such as real-time big data analytics.
• Storage Optimized: High IOPS for workloads involving extensive sequential read/write access to large datasets, such as data warehousing.
• Accelerated Computing: Specialized hardware accelerators (e.g., GPUs) for tasks like machine learning, graphics rendering, and high-performance simulations.

Q: What are Amazon Machine Images (AMIs)?

An Amazon Machine Image (AMI) is a pre-configured template that includes the operating system, application server, and applications needed to launch an EC2 instance. AMIs are region-specific and can include:

• One or more EBS snapshots or instance store-backed volumes.
• Permissions specifying which AWS accounts can use the AMI.
• Block device mapping for storage configuration.

AMIs serve as the foundational blueprint for deploying virtual servers quickly and consistently.

Q: How do you secure an EC2 instance?

Securing an EC2 instance involves several measures:

1. Security Groups: Control inbound and outbound traffic to instances by allowing only necessary access.
2. Key Pairs: Enable secure SSH access by generating and using a private key.
3. IAM Roles: Grant secure permissions to applications running on EC2 to access AWS APIs.
4. Network ACLs: Act as a subnet-level firewall to manage traffic.
5. Patch Management: Regularly apply updates and patches to the operating system.
6. Encryption: Use EBS encryption to secure data at rest.

Q: What is Elastic Load Balancing?

Elastic Load Balancing (ELB) distributes incoming application traffic across multiple EC2 instances, containers, or IP addresses. It ensures high availability, scalability, and security by dynamically adjusting to varying traffic loads. ELB supports three types of load balancers:

1. Application Load Balancer (ALB): Best for HTTP/HTTPS applications.
2. Network Load Balancer (NLB): Optimized for high-performance TCP traffic.
3. Classic Load Balancer (CLB): Supports basic load balancing across multiple EC2 instances.

Q: What are Spot Instances?

Spot Instances enable users to utilize unused EC2 capacity at up to 90% lower costs than On-Demand prices. They are ideal for:

• Applications with flexible start and end times.
• Workloads only feasible at very low compute prices.
• Urgent compute needs requiring additional capacity.

Spot Instances are especially suitable for batch jobs, data analysis, and testing environments.

Q: How can you vertically scale an EC2 instance?

Vertical scaling involves increasing the size of an EC2 instance to accommodate higher resource demands. For instance:

1. Stop the running instance.
2. Change the instance type to a more powerful configuration (e.g., upgrading from a t2.micro to an m5.large instance).
3. Restart the instance with the upgraded specifications.

Vertical scaling is particularly useful for applications that cannot scale horizontally across multiple instances.

Q: What are Reserved Instances in EC2?

Reserved Instances allow users to commit to using EC2 for a one- or three-year term in exchange for significant discounts compared to On-Demand pricing. They are ideal for steady-state workloads and offer three payment options: All Upfront, Partial Upfront, and No Upfront.

Q: What is the difference between On-Demand, Spot, and Reserved Instances?

• On-Demand: Pay for compute capacity by the hour or second, with no long-term commitment. Ideal for unpredictable workloads.
• Spot: Use unused EC2 capacity at a discounted rate. Suitable for flexible, interruptible workloads.
• Reserved: Commit to a long-term usage period for significant cost savings. Best for consistent, predictable workloads.

Q: What is an EC2 Auto Scaling Group?

An Auto Scaling Group (ASG) automatically adjusts the number of EC2 instances in a group based on defined policies, schedules, or health checks. It ensures applications maintain high availability and scale up or down as needed to handle traffic or cost requirements.

Q: What are Elastic IP Addresses?

Elastic IPs are static IPv4 addresses designed for dynamic cloud computing. They allow you to mask instance failures by quickly remapping the address to another instance in your account.

Q: What is the difference between Security Groups and Network ACLs?

• Security Groups: Operate at the instance level, stateful, and support rules for inbound and outbound traffic.
• Network ACLs: Operate at the subnet level, stateless, and evaluate inbound and outbound rules separately.

Q: What are EBS Volumes in EC2?

Elastic Block Store (EBS) provides persistent, block-level storage for EC2 instances. EBS volumes are durable and can be attached to instances in the same Availability Zone. They come in several types, such as General Purpose SSD, Provisioned IOPS SSD, and Magnetic.

Q: How do you horizontally scale EC2 instances?

Horizontal scaling involves adding more EC2 instances to your application’s architecture, often using an Auto Scaling Group combined with a Load Balancer to distribute traffic.

Q: What is Instance Metadata?

Instance metadata provides information about an EC2 instance that can be accessed from within the instance itself. It includes details such as the instance ID, security groups, and public IP. The metadata is accessed via a URL (http://169.254.169.254/latest/meta-data).

Q: What is a Placement Group in EC2?

A Placement Group determines how instances are placed on underlying hardware.

• Cluster Placement Group: Packs instances closely together for low-latency, high-performance networking.
• Spread Placement Group: Distributes instances across separate hardware to reduce the risk of simultaneous failure.
• Partition Placement Group: Divides instances into partitions, each on separate racks, to isolate failure.

Q: What is the difference between instance store and EBS-backed volumes?

• Instance Store: Temporary storage directly attached to the physical host, data is lost when the instance stops or terminates.
• EBS-backed Volumes: Persistent storage that remains even when the instance is stopped or terminated.

Q: What is EC2 Hibernate?

EC2 Hibernate allows an instance to pause and resume by saving its RAM to an EBS-backed volume. This is useful for applications that take a long time to initialize.

Q: How do you monitor EC2 instances?

Monitoring can be done through Amazon CloudWatch, which provides metrics like CPU utilization, network traffic, and disk I/O. Custom metrics can also be configured.

Q: What are EC2 instance lifecycle states?

1. Pending: Instance is being launched.
2. Running: Instance is operational.
3. Stopping: Instance is being stopped.
4. Stopped: Instance is stopped but can be restarted.
5. Terminated: Instance is permanently deleted.

Q: What are some best practices for EC2 cost optimization?

• Use Spot Instances for flexible workloads.
• Right-size instances based on workload requirements.
• Leverage Auto Scaling Groups to scale in/out dynamically.
• Use Reserved Instances or Savings Plans for predictable workloads.
• Optimize EBS usage by using cost-effective volume types.