1️⃣ IP Address
What is IP?
IP (Internet Protocol) address is a unique identifier assigned to a device on a network.
Example:
-
192.168.1.10(Private) -
18.221.32.84(Public)
Types:
- IPv4 – 32-bit (most common)
- IPv6 – 128-bit
Interview Q&A
Q: What is the difference between public and private IP?
A: Public IP is reachable over the internet. Private IP is used inside internal networks (VPC, office LAN).
Q: Can two servers have same IP?
A: Not in the same network. It causes IP conflict.
2️⃣ Port
What is a Port?
Port is a logical communication endpoint on a machine.
Examples:
- 80 → HTTP
- 443 → HTTPS
- 22 → SSH
- 3306 → MySQL
Interview Q&A
Q: What is the difference between IP and port?
A: IP identifies the machine. Port identifies the application on that machine.
3️⃣ Protocol
A protocol is a set of rules for communication.
Examples:
- HTTP
- HTTPS
- FTP
- TCP
- UDP
Q: What is TCP vs UDP?
A: TCP is reliable (connection-based). UDP is faster but connectionless.
4️⃣ Internet
The Internet is a global network of interconnected networks using TCP/IP protocol suite.
5️⃣ Virtual Machine (VM)
A Virtual Machine is a software-based computer that runs on a physical machine.
Examples:
- AWS EC2
- VMware
- VirtualBox
In AWS:
EC2 = virtual server.
Q: Difference between VM and container?
A: VM has full OS. Container shares host OS kernel.
6️⃣ SSD vs HDD
HDD (Hard Disk Drive)
- Mechanical
- Slower
- Cheaper
- Moving parts
SSD (Solid State Drive)
- No moving parts
- Much faster
- More expensive
- Used in cloud
Q: Why SSD is better for databases?
A: Faster IOPS and lower latency.
7️⃣ Types of Disks (Cloud / AWS Example)
- EBS – Block storage
- EFS – File storage
- S3 – Object storage
Disk Types:
- Magnetic
- SSD
- NVMe
- Network Attached
8️⃣ Temporary IP
Also called:
- Dynamic IP
- Ephemeral IP
In AWS:
- Public IP changes when EC2 stops/starts
- Elastic IP stays fixed
9️⃣ DNS (Domain Name System)
DNS converts domain names into IP addresses.
Example:
google.com → 142.250.190.78
Q: Why do we need DNS?
A: Humans remember names, not IP addresses.
🔟 DHCP (Dynamic Host Configuration Protocol)
Automatically assigns:
- IP
- Gateway
- DNS
Used in:
- Home routers
- Corporate networks
1️⃣1️⃣ SSH (Secure Shell)
Port: 22
Used to securely connect to servers.
Example:
ssh ubuntu@18.221.32.84
Q: Is SSH encrypted?
A: Yes.
1️⃣2️⃣ TLS / SSL
TLS = Transport Layer Security
SSL = Old version
Used in:
- HTTPS
- Secure communication
Q: Difference between HTTP and HTTPS?
A: HTTPS uses TLS encryption.
1️⃣3️⃣ HTTP
HyperText Transfer Protocol
- Stateless
- Port 80
Methods:
- GET
- POST
- PUT
- DELETE
1️⃣4️⃣ OSI Model (Very Important Interview Question)
7 Layers:
- Physical
- Data Link
- Network
- Transport
- Session
- Presentation
- Application
Easy Memory Trick:
All People Seem To Need Data Processing
Important Layers for DevOps:
- Layer 3 → IP
- Layer 4 → TCP/UDP
- Layer 7 → HTTP
Q: At which layer does TCP work?
A: Transport layer (Layer 4)
Q: At which layer does IP work?
A: Network layer (Layer 3)
🔥 Advanced DevOps Interview Questions
1. What happens when you type google.com in browser?
Answer:
- DNS lookup
- TCP handshake
- TLS handshake
- HTTP request
- Server response
2. Explain 3-way TCP handshake
SYN → SYN-ACK → ACK
3. What is latency?
Time taken for packet to travel.
4. What is bandwidth?
Amount of data that can be transferred.
5. What is NAT?
Network Address Translation converts private IP to public IP.
🎯 Real DevOps Scenario Question
Q: Application not reachable. How do you troubleshoot?
Answer steps:
- Check DNS
- Check security group
- Check port open (
ss -tulnp) - Check firewall
- Check application logs
- Check load balancer
✅ PART 1 — ALB (Application Load Balancer)
🔹 1. What is ALB?
Answer:
ALB (Application Load Balancer) distributes incoming HTTP/HTTPS traffic across multiple targets such as EC2 instances, containers, or IP addresses.
It works at Layer 7 (Application Layer) and supports advanced routing like path-based and host-based routing.
🔹 2. Difference between ALB and NLB?
| ALB | NLB |
|---|---|
| Layer 7 | Layer 4 |
| HTTP/HTTPS | TCP/UDP |
| Path-based routing | No advanced routing |
| Web apps, microservices | High-performance, low latency systems |
🔹 3. What is a Target Group?
A logical group of instances or IPs where ALB sends traffic.
Health checks are configured at the target group level.
🔹 4. What is a Listener?
A process that checks for connection requests on a specific port (80, 443) and forwards traffic to target groups.
🔹 5. What is Path-Based Routing?
Routing based on URL path:
example.com/api → API servers
example.com/app → App servers
Very common in microservices architecture.
🔹 6. What is Host-Based Routing?
Routing based on hostname:
api.example.com → API service
app.example.com → Frontend
🔹 7. How does ALB perform health checks?
ALB sends periodic HTTP requests to a configured path like:
/health
If instance fails multiple checks → marked unhealthy → traffic stops.
🔹 8. What is Cross-Zone Load Balancing?
ALB distributes traffic evenly across instances in multiple Availability Zones.
Improves high availability.
🔹 9. What is Sticky Session?
Also called session affinity.
ALB forwards requests from the same client to the same instance using cookies.
Used for stateful apps.
🔹 10. What is Deregistration Delay?
When instance is removed, ALB waits (default 300 sec) before fully stopping traffic.
Prevents connection drops.
🔹 11. Why ALB returns 502?
- Application crashed
- Wrong port in target group
- Container not listening
- Security group issue
🔹 12. Why ALB returns 503?
- No healthy targets
- All instances unhealthy
- Target group empty
🔹 13. Why ALB returns 504?
- Backend timeout
- Application too slow
- Long-running query
🔹 14. How do you secure ALB?
- Attach Security Group
- Use HTTPS (ACM certificate)
- Enable WAF
- Restrict inbound traffic
- Enable access logs
🔹 15. How does ALB integrate with EKS?
- Kubernetes Ingress Controller creates ALB
- ALB routes traffic to pods via NodePort or IP targets
- Used for microservices
✅ PART 2 — ASG (Auto Scaling Group)
🔹 1. What is ASG?
ASG automatically adjusts number of EC2 instances based on load.
Ensures:
- High availability
- Fault tolerance
- Cost optimization
🔹 2. What is Launch Template?
Blueprint for EC2 instances:
- AMI
- Instance type
- Security group
- Key pair
- User data
🔹 3. What is Desired Capacity?
Number of instances ASG tries to maintain.
🔹 4. What are Min and Max size?
Minimum and maximum number of instances allowed.
Example:
Min: 2
Desired: 3
Max: 6
🔹 5. What is Scaling Policy?
Defines when to scale:
- Target tracking (CPU 70%)
- Step scaling
- Scheduled scaling
🔹 6. What metric is commonly used?
- CPUUtilization
- NetworkIn/Out
- RequestCount (via ALB)
- Custom CloudWatch metrics
🔹 7. What happens if instance becomes unhealthy?
ASG terminates it and launches a new one automatically.
🔹 8. What is Cooldown Period?
Time ASG waits after scaling event before scaling again.
Prevents rapid scaling.
🔹 9. What is lifecycle hook?
Pauses instance during launch/terminate to run custom scripts.
Used for:
- Logging
- Configuration
- Data draining
🔹 10. How ASG works with ALB?
- ASG attaches to target group
- ALB sends traffic
- If load increases → ASG launches new instance
- ALB automatically registers it
✅ PART 3 — RDS (Relational Database Service)
🔹 1. What is RDS?
Managed database service in AWS.
Supports:
- MySQL
- PostgreSQL
- MariaDB
- Oracle
- SQL Server
- Aurora
🔹 2. Why use RDS instead of EC2 database?
RDS provides:
- Automatic backups
- Patching
- Monitoring
- Multi-AZ
- Failover
- Snapshots
Less operational overhead.
🔹 3. What is Multi-AZ?
RDS creates standby replica in another AZ.
If primary fails → automatic failover.
🔹 4. What is Read Replica?
Read-only copy of database.
Used to:
- Improve read performance
- Offload reporting queries
🔹 5. Difference between Multi-AZ and Read Replica?
| Multi-AZ | Read Replica |
|---|---|
| For HA | For performance |
| Automatic failover | Manual promotion |
| Synchronous | Asynchronous |
🔹 6. What are RDS backups?
- Automated backups (retention 1–35 days)
- Manual snapshots
🔹 7. What is RDS endpoint?
DNS address used to connect to database.
Example:
database-1.cchwko406tle.us-east-1.rds.amazonaws.com
🔹 8. How do you secure RDS?
- Place in private subnet
- Security group restrict port 3306
- Enable encryption (KMS)
- Store password in Secrets Manager
🔹 9. What causes RDS high latency?
- Slow queries
- Missing indexes
- High connections
- CPU spike
- Disk IOPS limit
🔹 10. How to troubleshoot RDS connection timeout?
- Check security group
- Check subnet routing
- Check NACL
- Check if public access enabled
- Check port
✅ PART 4 — Aurora
🔹 1. What is Aurora?
AWS high-performance relational database compatible with MySQL and PostgreSQL.
🔹 2. Why Aurora is faster?
- Distributed storage
- 6 copies across 3 AZs
- Auto scaling storage
- Optimized engine
🔹 3. Difference between RDS MySQL and Aurora?
| RDS MySQL | Aurora |
|---|---|
| Traditional engine | Cloud-native |
| Storage manual scaling | Auto-scaling |
| Slower replication | Faster replication |
🔹 4. What is Aurora cluster?
Consists of:
- 1 writer instance
- Multiple reader instances
- Shared distributed storage
🔹 5. What is Aurora endpoint types?
- Cluster endpoint (writer)
- Reader endpoint
- Custom endpoint
🔹 6. What is Aurora Serverless?
On-demand auto-scaling database.
Scales automatically based on load.
✅ PART 5 — Advanced Scenario Questions
🔹 Scenario 1
Application crashes when scaling.
What do you check?
- Health check path
- User data script
- Instance logs
- CPU spike
- Memory usage
🔹 Scenario 2
High database CPU.
What do you check?
- Slow query log
- Index usage
- Connection count
- Long transactions
🔹 Scenario 3
ALB healthy but users can’t access.
Check:
- Security groups
- Route table
- Internet Gateway
- DNS
🔹 Scenario 4
ASG not scaling.
Check:
- CloudWatch alarm
- Scaling policy
- Metric threshold
- Launch template validity
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