.NET Production Diagnostics Lab

A small ASP.NET Core diagnostics lab showing common production-style problems, how to detect them, and how to improve reliability, performance, and observability.

This repository is a hands-on lab, not a production template and not an architecture showcase.

What this repo demonstrates

• Slow data access caused by inefficient queries
• N+1 / chatty data access caused by per-row database calls
• Missing cancellation and timeout behavior
• Sync-over-async / blocking request handling
• Poor observability and weak logging
• Reliability issues caused by unsafe external dependency calls
• Retry storms caused by uncontrolled retries
• Memory pressure caused by building large responses in memory
• Configuration problems detected too late instead of at startup
• Missing health checks for operational visibility
• Startup work that fails silently instead of failing fast
• Logging or audit sink failures leaking into business operations
• Request body memory pressure caused by buffering large uploads

How to run

dotnet restore
dotnet run --project src/DiagnosticsLab.Api

The API uses SQLite and creates local seed data automatically.

Scenarios

1. Slow data access

• Problem: GET /api/orders/slow?customerId=42
• Improved: GET /api/orders/improved?customerId=42

2. Cancellation

• Problem: GET /api/reports/slow
• Improved: GET /api/reports/cancellable

3. Observability

• Problem: POST /api/payments/problem
• Improved: POST /api/payments/observable

4. External dependency reliability

• Problem: GET /api/shipping/problem?country=CZ
• Improved: GET /api/shipping/resilient?country=CZ

5. N+1 / chatty data access

• Problem: GET /api/customers/problem?take=25
• Improved: GET /api/customers/improved?take=25

6. Blocking request handling

• Problem: GET /api/blocking/problem?delayMs=500
• Improved: GET /api/blocking/improved?delayMs=500

7. Retry storm / controlled retry

• Problem: GET /api/inventory/problem?sku=FAIL
• Improved: GET /api/inventory/improved?sku=FAIL

8. Large response allocation / streaming

• Problem: GET /api/exports/problem?rows=1000
• Improved: GET /api/exports/improved?rows=1000

9. Configuration validation

• Problem: GET /api/config/problem
• Improved: application startup validates ExternalServices:BillingApiBaseUrl

10. Health checks

• Improved: GET /health/live and GET /health/ready

11. Startup exception handling

• Problem: GET /api/startup/problem
• Improved: GET /api/startup/improved

12. Logging failure isolation

• Problem: POST /api/audit/problem
• Improved: POST /api/audit/improved

13. Request body memory pressure

• Problem: POST /api/uploads/problem
• Improved: POST /api/uploads/improved

Tests

dotnet test

The tests include smoke checks, scenario checks, startup validation checks, and endpoint behavior checks.

Notes

The examples are intentionally small. The goal is to make production-style problems easy to see, explain, and improve.