Response Caching in ASP.NET Core (.NET 10)

Server-side, client-side, and proxy caching in one beginner-friendly sample — 7 practical Minimal API endpoints covering every caching scenario with Swagger/OpenAPI.

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🎯 What You'll Learn

• How to configure Response Caching Middleware in ASP.NET Core
• How to cache responses on the server, client, and proxy with Cache-Control
• How to use Vary by query key for query-parameter-dependent caching
• How to use Vary by header for header-based cache variations
• How to disable caching for sensitive or dynamic endpoints
• How to inspect cache behaviour using Cache-Control, Vary, and Age response headers

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🗺️ Architecture Overview

Client Request
      │
      ▼
┌─────────────────────────────────────────────────────────────┐
│                     Client Request                          │
└─────────────────────┬───────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────────────┐
│              Response Caching Middleware                    │
│  ┌─────────────────────────────────────────────────────┐   │
│  │  Cached response exists?                            │   │
│  │  YES → return cached response (Age header added)    │   │
│  │  NO  → forward to endpoint → cache the response     │   │
│  └─────────────────────────────────────────────────────┘   │
└─────────────────────┬───────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────────────┐
│                   Minimal API Endpoints                     │
│  Products / User Profile / Time / Random / Private / Login  │
└─────────────────────┬───────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────────────┐
│              HTTP Response + Cache Headers                  │
│         Cache-Control · Vary · Age · ETag                   │
└─────────────────────────────────────────────────────────────┘

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📋 Endpoints & Caching Strategies

Endpoint	Method	Cache Strategy	Duration
/api/products	GET	Server + public	60 seconds
/api/products/by-category	GET	Vary by category query	120 seconds
/api/user-profile	GET	Client-only	300 seconds
/api/time	GET	Vary by Accept-Language header	10 seconds
/api/random-number	GET	No cache (no-store)	—
/api/private-data	GET	No cache (private)	—
/api/login	POST	No cache (security)	—
/api/cache-status	GET	No cache (diagnostic)	—

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📁 Project Structure

dotnet-response-caching/
├── DotNetResponseCaching.sln
└── src/
    └── DotNetResponseCaching.Api/
        ├── Program.cs           # Middleware setup, endpoints, cache profiles
        ├── appsettings.json
        └── Properties/
            └── launchSettings.json

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🛠️ Prerequisites

• .NET 10 SDK
• Any IDE: Visual Studio 2022+, VS Code, or JetBrains Rider

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⚡ Quick Start

# Clone the repo
git clone https://github.com/codingdroplets/dotnet-response-caching.git
cd dotnet-response-caching

# Run the API
dotnet run --project src/DotNetResponseCaching.Api

# Open Swagger UI → http://localhost:5000/swagger

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🔧 How It Works

Step 1 — Register Middleware and Cache Profiles

builder.Services.AddResponseCaching();

builder.Services.AddControllers(options =>
{
    options.CacheProfiles.Add("Default",
        new CacheProfile { Duration = 60 });       // 60s, any location
    options.CacheProfiles.Add("Short",
        new CacheProfile { Duration = 30, Location = ResponseCacheLocation.Client });
    options.CacheProfiles.Add("Long",
        new CacheProfile { Duration = 300, VaryByQueryKeys = new[] { "category", "page" } });
});

// Must be placed before routing middleware
app.UseResponseCaching();

Step 2 — Decorate Endpoints with Cache Behaviour

// Server-side cache for 60 seconds
app.MapGet("/api/products", GetProducts)
   .CacheOutput(p => p.Expire(TimeSpan.FromSeconds(60)));

// Vary by query key — each category cached separately
app.MapGet("/api/products/by-category", GetByCategory)
   .CacheOutput(p => p.Expire(TimeSpan.FromSeconds(120)).SetVaryByQuery("category"));

// Client-only — no server-side store
app.MapGet("/api/user-profile", GetUserProfile)
   .CacheOutput(p => p.Expire(TimeSpan.FromSeconds(300)).NoStore());

// No caching for sensitive/dynamic endpoints
app.MapPost("/api/login", Login)
   .CacheOutput(p => p.NoStore());

Step 3 — Read the Cache Headers

Make a request, then check response headers:

curl -I http://localhost:5000/api/products
# Cache-Control: public, max-age=60
# Age: 0   ← first hit (not yet cached)

curl -I http://localhost:5000/api/products
# Age: 4   ← served from cache

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🤔 Cache Headers Explained

Header	Description
Cache-Control	Directives: public, private, no-store, max-age
Vary	Which request headers affect cache key (Accept-Language, etc.)
Age	Seconds this response has been in cache
ETag	Identifier for a specific version of the content

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🤔 Response Caching vs Related Concepts

Type	What It Caches	Storage	Use When
Response Caching	HTTP responses (this sample)	Server memory / proxy	Public, rarely-changing API responses
Output Caching	Entire rendered output	In-memory (server)	Razor Pages, full page caching
In-Memory Caching	Arbitrary objects (IMemoryCache)	Server memory	Internal data, computed results
Distributed Caching	Arbitrary objects (Redis / SQL)	External store	Multi-server / load-balanced apps

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📚 References

• Response caching in ASP.NET Core — Microsoft Learn
• Cache-Control directives — MDN Web Docs
• HTTP Caching — RFC 9111

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📄 License

This project is licensed under the MIT License.

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