Technical Lead Scenario-Based Interview Questions & Answers (.NET Core + Azure)
Scenario 1: Designing a New Enterprise Application
Interviewer
Your company wants to build a Loan Management System used by 500,000 customers. How would you design the architecture?
Expected Answer
First I gather functional and non-functional requirements.
Functional:
Customer Registration
Loan Application
Approval Workflow
Payment
Notifications
Non-functional:
High Availability
Scalability
Security
Performance
Disaster Recovery
Architecture:
Angular
|
API Gateway (Azure APIM)
|
-----------------------------
Identity Service
Loan Service
Payment Service
Notification Service
Document Service
-----------------------------
Azure Service Bus
Azure SQL
Blob Storage
Redis Cache
Application Insights
Patterns:
Clean Architecture
DDD
CQRS
Repository
Unit of Work
Event Driven
Azure Services
Azure App Service
Azure SQL
Azure Key Vault
Azure Service Bus
Azure Storage
Azure Monitor
Application Insights
This architecture supports independent deployment and scaling.
Scenario 2: Microservice Communication
Interviewer
Service A needs customer details from Service B.
Would you call it synchronously or asynchronously?
Answer
Depends on business requirement.
If immediate response required
Order Service
↓
Customer Service (REST API)
Use:
REST
gRPC
If eventual consistency acceptable
Order Created
↓
Azure Service Bus
↓
Customer Service
↓
Notification Service
↓
Audit Service
Benefits
Loose coupling
Retry
High availability
Independent scaling
Scenario 3: API Performance Issue
Interviewer
One API takes 18 seconds.
How will you investigate?
Answer
My investigation sequence:
Step 1
Application Insights
Check
Dependency calls
Exceptions
Slow SQL
Step 2
Database
Check
Execution Plan
Missing Index
Blocking
Deadlock
Step 3
Code
Look for
foreach(...)
{
await repository.GetById();
}
N+1 problem.
Instead
Single Query
Step 4
Caching
Redis
Memory Cache
Step 5
Load Testing
Azure Load Test
JMeter
Finally optimize.
Scenario 4: Production is Down
Interviewer
Production suddenly becomes unavailable.
What do you do?
Answer
Never panic.
Follow Incident Process.
Step 1
Verify
Azure Health
App Service
SQL
Service Bus
Step 2
Rollback if deployment caused issue.
Step 3
Collect Logs
Application Insights
Azure Monitor
Step 4
Temporary Fix
Scale Out
Restart unhealthy instances
Disable problematic feature
Step 5
Root Cause Analysis
Document
Prevent recurrence.
Scenario 5: Azure SQL Database Reaches 100% CPU
Interviewer
Users complain application is slow.
Azure SQL CPU is 100%.
How do you solve it?
Answer
Check
Top Queries
Execution Plans
Missing Indexes
Deadlocks
Blocking Sessions
Large Table Scan
Optimize
Indexes
Pagination
Caching
Read-only replicas
Partitioning
Increase DTU/vCore only if required.
Scenario 6: Team Writes Duplicate Logic
Interviewer
Every developer writes validation differently.
What will you do?
Answer
As Technical Lead
I introduce
Coding Standards
Common Validation Library
Reusable NuGet Package
Static Code Analysis
Pull Request Guidelines
Every PR goes through review.
Consistency improves.
Scenario 7: Security Review
Interviewer
Security team found secrets inside appsettings.json.
How do you fix it?
Answer
Never store secrets.
Move
Connection String
API Keys
Certificates
Passwords
To
Azure Key Vault
Use
Managed Identity
Benefits
Secret Rotation
Encryption
Audit Trail
Scenario 8: API Authentication
Interviewer
How do you secure APIs?
Answer
Authentication
Azure AD
JWT
Authorization
Role Based Access
Policy Based Authorization
Claims
Other security
HTTPS
Rate Limiting
Input Validation
OWASP
Key Vault
APIM
Scenario 9: Scaling
Interviewer
Traffic increases 20 times during Black Friday.
How will your application survive?
Answer
Use
Stateless APIs
Redis Cache
Autoscaling
Azure App Service Scale Out
Azure SQL Elastic Pool
Azure Service Bus
CDN
Blob Storage
Horizontal scaling.
Scenario 10: Event Driven Architecture
Interviewer
Customer places an order.
Five services need notification.
How will you design?
Answer
Instead of
Order
↓
Inventory
↓
Payment
↓
Email
↓
Analytics
↓
CRM
Use
Order Service
↓
Publish Event
↓
Azure Service Bus Topic
↓
Inventory
↓
Payment
↓
Email
↓
Analytics
↓
CRM
Much more scalable.
Scenario 11: Code Review
Interviewer
What do you check during code review?
Answer
I check
✔ SOLID
✔ Naming
✔ Security
✔ Performance
✔ Exception Handling
✔ Logging
✔ Unit Tests
✔ Async
✔ Disposal
✔ SQL Injection
✔ Reusability
Scenario 12: Logging Strategy
Interviewer
How do you implement logging?
Answer
Levels
Information
Warning
Error
Critical
Use
ILogger
Serilog
Application Insights
Correlation ID
Never log passwords.
Scenario 13: Production Bug
Interviewer
A bug exists only in Production.
Not reproducible locally.
How do you investigate?
Answer
Check
Logs
Telemetry
Configuration
Environment Variables
Version
Feature Flags
Data Differences
Database
Application Insights Transaction Search.
Scenario 14: API Versioning
Interviewer
Old clients still use v1.
New features in v2.
How do you support both?
Answer
api/v1/customer
api/v2/customer
Deprecate older versions gradually.
Communicate timeline.
Scenario 15: CI/CD
Interviewer
Explain your deployment pipeline.
Answer
Developer
↓
Git
↓
Pull Request
↓
Build
↓
Unit Test
↓
SonarQube
↓
Publish Artifact
↓
Deploy Dev
↓
QA
↓
UAT
↓
Production Approval
↓
Production
Scenario 16: Production Deployment Failed
Interviewer
Half deployment completed.
Users affected.
Now what?
Answer
Blue-Green Deployment
Rollback
Database backward compatibility
Feature Flags
Health Check
Smoke Test
Scenario 17: Team Conflict
Interviewer
Two senior developers disagree on architecture.
What do you do?
Answer
Arrange technical discussion.
Compare
Performance
Maintainability
Scalability
Security
Development effort
Prototype if needed.
Decision based on facts.
Not opinions.
Scenario 18: Slow Microservice
Interviewer
One service delays every request.
Answer
Check
Dependency Calls
Database
Redis
Thread Pool
Memory
GC
CPU
Distributed Tracing
Application Insights
Scenario 19: Legacy Monolith Migration
Interviewer
Company wants Microservices.
How will you migrate?
Answer
Use
Strangler Pattern
Extract modules one by one
Customer
Order
Payment
Notification
Eventually retire monolith.
Scenario 20: Observability
Interviewer
How do you monitor application health?
Answer
Metrics
CPU
Memory
Response Time
Availability
Dependency Failures
Exception Rate
Dashboard
Azure Monitor
Application Insights
Alerts
Teams
SMS
Scenario 21: Handling High Traffic During a Flash Sale
Interviewer
Your e-commerce site receives 10x normal traffic during a flash sale. Checkout APIs start timing out. What immediate and long-term actions would you take?
Answer
Immediate actions:
Scale out Azure App Service instances.
Increase Azure SQL compute if it's the bottleneck.
Enable/verify Redis caching for frequently accessed data.
Queue non-critical operations (emails, analytics) using Azure Service Bus.
Monitor live metrics in Application Insights.
Long-term improvements:
Optimize slow database queries and indexing.
Implement autoscaling rules.
Use CDN for static content.
Add load testing to CI/CD.
Introduce asynchronous processing where appropriate.
Scenario 22: Production Memory Leak
Interviewer
After a few days of uptime, your API becomes slow and eventually crashes with OutOfMemoryException. How do you investigate?
Answer
Check Application Insights memory metrics.
Capture memory dumps.
Analyze with Visual Studio Diagnostic Tools or dotMemory.
Look for:
Undisposed
IDisposableobjects.Static collections growing indefinitely.
Event handler leaks.
Large object allocations.
Fix resource disposal and validate with load testing.
Scenario 23: Breaking Database Schema Changes
Interviewer
A database schema change is required, but older application versions are still running during deployment. How do you avoid downtime?
Answer
Follow backward-compatible database changes.
Add new columns before removing old ones.
Deploy application changes that support both schemas.
Migrate data in the background.
Remove deprecated schema only after all instances are updated.
Scenario 24: Third-Party API Failure
Interviewer
Your payment provider is intermittently unavailable. How do you prevent your application from failing?
Answer
Use resilience patterns:
Retry with exponential backoff.
Circuit Breaker.
Timeout policies.
Fallback responses where appropriate.
Queue requests if business rules allow.
Monitor failures and alert operations.
Common implementation: Polly in .NET.
Scenario 25: Mentoring a Junior Team
Interviewer
A junior developer repeatedly introduces bugs. As a Technical Lead, how do you handle it?
Answer
Review the code together instead of only rejecting PRs.
Explain the reasoning behind feedback.
Pair program on complex features.
Recommend learning resources.
Gradually increase responsibility.
Track improvement through regular one-on-one sessions.
This approach improves both code quality and team growth.
Technical Lead Interview Tips
Interviewers also evaluate how you think, not just what you know. When answering scenario questions:
Clarify assumptions before proposing a solution.
Consider scalability, security, performance, and maintainability together.
Mention trade-offs and why you chose a particular approach.
Include Azure services, design patterns, and DevOps practices where relevant.
Explain how you would communicate with stakeholders and lead the team during incidents.
These scenarios closely reflect the responsibilities you listed and are typical of Technical Lead interviews for enterprise .NET and Azure roles.
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