DEV Community

Aisalkyn Aidarova
Aisalkyn Aidarova

Posted on

This is a very strong DevOps / Cloud Engineer interview preparation list.

1. What is Hardware?

Hardware is any physical component of a computer system.

Examples:

  • CPU
  • RAM
  • SSD/HDD
  • Motherboard
  • Network Card
  • Power Supply
  • Keyboard
  • Monitor

Think of hardware as everything you can physically touch.

2. What is Software?

Software is a set of instructions that tell hardware what to do.

Examples:

Operating Systems

  • Linux
  • Windows
  • macOS

Applications

  • Browser
  • Microsoft Word
  • Zoom
  • Slack

Programming Languages

  • Python
  • Java
  • JavaScript

3. What is CPU?

CPU = Central Processing Unit

CPU is the brain of the computer.

Responsibilities:

  • Execute instructions
  • Perform calculations
  • Process requests
  • Run applications

Example:

When opening Chrome:

  1. CPU receives command
  2. CPU processes instruction
  3. RAM stores temporary data
  4. Chrome appears on screen

Interview Question:

What happens if CPU reaches 100% utilization?

Answer:

  • System becomes slow
  • Applications freeze
  • Response time increases
  • Requests queue up

Troubleshooting:

top
htop
Enter fullscreen mode Exit fullscreen mode

Check CPU-consuming processes.

4. What is RAM?

RAM = Random Access Memory

Temporary memory.

Stores:

  • Running applications
  • Active processes
  • Temporary data

Example:

When opening:

  • Chrome
  • VS Code
  • Slack

All are loaded into RAM.

Important:

RAM is volatile.

If power is lost:

RAM data disappears.

Interview Question:

Difference between RAM and SSD?

RAM:

  • Faster
  • Temporary
  • Volatile

SSD:

  • Slower than RAM
  • Permanent
  • Persistent

5. What is SSD?

SSD = Solid State Drive

Permanent storage.

Stores:

  • OS
  • Applications
  • Documents
  • Databases

Advantages:

  • Faster than HDD
  • No moving parts
  • Better performance

Commands:

df -h
lsblk
Enter fullscreen mode Exit fullscreen mode

6. What is a Server?

A server is a computer that provides services to other computers.

Examples:

  • Web Server
  • Database Server
  • Mail Server

Example:

User requests:

www.amazon.com
Enter fullscreen mode Exit fullscreen mode

Request reaches server.

Server returns webpage.

7. What is a Virtual Machine?

VM = Virtual Machine

A software-based computer.

Runs on physical hardware.

Example:

One physical server:

64 CPU
256 GB RAM
Enter fullscreen mode Exit fullscreen mode

Can host:

VM1
VM2
VM3
VM4
Enter fullscreen mode Exit fullscreen mode

Benefits:

  • Isolation
  • Cost savings
  • Scalability

Examples:

  • VMware
  • VirtualBox
  • Hyper-V
  • EC2

8. What is Linux?

Linux is an operating system.

Responsibilities:

  • Process management
  • Memory management
  • User management
  • File system management

Common Commands:

pwd
ls
cd
mkdir
rm
cp
mv
Enter fullscreen mode Exit fullscreen mode

Process Commands:

ps -ef
top
htop
kill -9 PID
Enter fullscreen mode Exit fullscreen mode

Disk Commands:

df -h
du -sh
Enter fullscreen mode Exit fullscreen mode

Memory:

free -m
Enter fullscreen mode Exit fullscreen mode

9. Linux Troubleshooting

Server Slow

Check:

top
Enter fullscreen mode Exit fullscreen mode

Questions:

  • CPU high?
  • Memory high?
  • Disk full?

Disk Full 

df -h
Enter fullscreen mode Exit fullscreen mode

Find large files:

du -sh /*
Enter fullscreen mode Exit fullscreen mode

Application Down

Check:

systemctl status nginx
Enter fullscreen mode Exit fullscreen mode

Logs:

journalctl -xe
Enter fullscreen mode Exit fullscreen mode

10. What is Networking?

Networking allows devices to communicate.

Example:

Laptop → Router → Internet → Server

11. What is IP Address?

Unique address assigned to device.

Example:

192.168.1.10
Enter fullscreen mode Exit fullscreen mode

Like a home address.

12. What is Router?

Router connects different networks.

Example:

Home Network
     |
 Router
     |
Internet
Enter fullscreen mode Exit fullscreen mode

Functions:

  • Route traffic
  • NAT
  • Internet connectivity

13. What is Switch?

Switch connects devices within same network.

Example:

PC1
PC2
Printer
Server
Enter fullscreen mode Exit fullscreen mode

All connected to switch.

Switch uses MAC addresses.

Router uses IP addresses.

Interview Question:

Router vs Switch?

Switch:

  • Same network
  • MAC address

Router:

  • Different networks
  • IP address

14. What is Load Balancer?

Distributes traffic across servers.

Example:

Users
  |
Load Balancer
 |
 |---- Server1
 |---- Server2
 |---- Server3
Enter fullscreen mode Exit fullscreen mode

Benefits:

  • High Availability
  • Scalability
  • Fault Tolerance

AWS Types:

  • ALB
  • NLB

15. What is EC2?

EC2 = Elastic Compute Cloud

AWS virtual machine service.

Features:

  • CPU
  • RAM
  • Storage
  • Networking

Use cases:

  • Web servers
  • Applications
  • Databases

Entity: Amazon Web Services EC2 is one of the core compute services.

16. What is EBS?

EBS = Elastic Block Store

Storage attached to EC2.

Think:

EC2 = Computer
EBS = Hard Drive
Enter fullscreen mode Exit fullscreen mode

Characteristics:

  • Block storage
  • Persistent
  • Snapshot support

Types:

  • gp3
  • io2
  • st1

Interview:

Can EBS exist without EC2?

Yes.

Volume remains after instance termination if configured.

17. What is EFS?

EFS = Elastic File System

Shared storage.

Many EC2s can mount same filesystem.

Example:

EC2-1
EC2-2
EC2-3
   |
   EFS
Enter fullscreen mode Exit fullscreen mode

Use:

  • Shared files
  • Web content
  • Kubernetes shared storage

Difference:

EBS:

  • Single instance typically

EFS:

  • Multiple instances

18. What is S3?

S3 = Simple Storage Service

Object storage.

Stores:

  • Images
  • Videos
  • Logs
  • Backups

Features:

  • Highly durable
  • Scalable
  • Versioning
  • Lifecycle Policies

Example:

Store:

photo.jpg
backup.zip
logs.tar
Enter fullscreen mode Exit fullscreen mode

inside bucket.

19. What is IAM?

IAM = Identity and Access Management

Controls permissions.

Components:

IAM User

Permanent identity.

IAM Group

Collection of users.

IAM Policy

Permissions document.

IAM Role

Temporary permissions.

Interview:

User vs Role?

User:

  • Permanent

Role:

  • Temporary

20. What is SAML?

SAML = Security Assertion Markup Language

Used for Single Sign-On (SSO).

Example:

Employee logs into:

  • Company Portal

Automatically accesses:

  • AWS
  • Salesforce
  • Workday

without re-entering password.

Flow:

User
 |
Identity Provider
 |
AWS
Enter fullscreen mode Exit fullscreen mode

Examples:

  • Okta
  • Microsoft Entra ID

21. What is OpenID Connect (OIDC)?

Modern authentication protocol.

Built on OAuth 2.0.

Used by:

  • Google Login
  • GitHub Login
  • Microsoft Login

Example:

Login with Google
Enter fullscreen mode Exit fullscreen mode

Website trusts Google.

Google verifies identity.

Website receives token.

Difference:

SAML:

  • XML
  • Enterprise

OIDC:

  • JSON/JWT
  • Modern Cloud Apps

22. What is API Gateway?

API Gateway receives API requests.

Example:

User
 |
API Gateway
 |
Lambda
Enter fullscreen mode Exit fullscreen mode

Responsibilities:

  • Authentication
  • Authorization
  • Rate limiting
  • Routing

23. What is Lambda?

Lambda is serverless compute.

You upload code.

AWS manages servers.

Example:

User Uploads File
      |
      S3
      |
   Lambda
Enter fullscreen mode Exit fullscreen mode

Lambda executes automatically.

Benefits:

  • No server management
  • Pay only when used
  • Auto scaling

24. What is Auto Scaling Group (ASG)?

Automatically adjusts EC2 count.

Example:

Traffic increases:

2 EC2
→
6 EC2
Enter fullscreen mode Exit fullscreen mode

Traffic decreases:

6 EC2
→
2 EC2
Enter fullscreen mode Exit fullscreen mode

Benefits:

  • Cost savings
  • High availability

25. Most Common Troubleshooting Questions

Website Not Loading

Check:

ping
nslookup
curl
Enter fullscreen mode Exit fullscreen mode

Questions:

  • DNS working?
  • Server up?
  • Application running?
  • Security Group open?

EC2 Reachable but Website Not Working

Check:

systemctl status nginx
Enter fullscreen mode Exit fullscreen mode

Check:

netstat -tulpn
Enter fullscreen mode Exit fullscreen mode

or

ss -tulpn
Enter fullscreen mode Exit fullscreen mode

Verify service listening on port 80.

High CPU 

top
Enter fullscreen mode Exit fullscreen mode

Find process.

Possible causes:

  • Infinite loop
  • Memory leak
  • Too many requests

High Memory 

free -m
Enter fullscreen mode Exit fullscreen mode

Check:

ps aux --sort=-%mem
Enter fullscreen mode Exit fullscreen mode

Cannot SSH to Server

Verify:

  1. Instance running
  2. Security Group allows port 22
  3. Correct key pair
  4. NACL allows traffic
  5. Route table correct

Internet Not Working

Check:

ping 8.8.8.8
Enter fullscreen mode Exit fullscreen mode

If works:

DNS issue.

Check:

nslookup google.com
Enter fullscreen mode Exit fullscreen mode

Most Important Interview Question

Explain how a user opens a website from browser.

Answer:

  1. User types URL.
  2. DNS resolves domain to IP.
  3. Browser sends request.
  4. Router forwards traffic.
  5. Internet routes packet.
  6. Load Balancer receives request.
  7. Load Balancer sends request to EC2.
  8. Application processes request.
  9. Database returns data.
  10. EC2 sends response back.
  11. Browser displays webpage.

This question tests networking, DNS, servers, load balancers, applications, and cloud knowledge all at once.

Top comments (0)