Web API - Caching

Note: Response/Output cache handled by their respective middlewares and do not hit controller in subsequent requests until cache invalidated.

Data Cache (IMemorycache, Memcache, Redis): Managed by code, you check in code if data available in cache then serve else reproduce and serve.

1. Output Caching (Recommended for .NET 7+)

Starting in ASP.NET Core 7+, Microsoft introduced built-in Output Caching Middleware, which is the best way to cache full API responses.

Step 1: Register Output Caching

In Program.cs:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOutputCache();

var app = builder.Build();

app.UseOutputCache();

app.MapControllers();

app.Run();

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Step 2: Apply Caching to an Endpoint

[HttpGet]
[OutputCache(Duration = 60)]
public IActionResult GetProducts()
{
    return Ok(GetProductsFromDatabase());
}

🔹 This caches the response for 60 seconds.
🔹 Works great for GET endpoints.

---

Advanced Example (Custom Policy)

builder.Services.AddOutputCache(options =>
{
    options.AddPolicy("MyPolicy", policy =>
        policy.Expire(TimeSpan.FromMinutes(5))
              .SetVaryByQuery("category"));
});

Then:

[OutputCache(PolicyName = "MyPolicy")]

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2. Response Caching (HTTP Cache Headers)

This uses HTTP headers like Cache-Control. It works with browser/proxy caching.

Enable Middleware

builder.Services.AddResponseCaching();
app.UseResponseCaching();

Use Attribute

[ResponseCache(Duration = 60)]
[HttpGet]
public IActionResult GetProducts()
{
    return Ok(data);
}

🔹 This sets HTTP headers.
🔹 It does NOT cache on the server by default.
🔹 Good for public APIs.

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3. Data Cache 
In-Memory Caching (IMemoryCache)

Best when you want to cache data, not full HTTP responses.

Register

builder.Services.AddMemoryCache();

Use in Controller

private readonly IMemoryCache _cache;

public ProductsController(IMemoryCache cache)
{
    _cache = cache;
}

[HttpGet]
public IActionResult GetProducts()
{
    if (!_cache.TryGetValue("products", out List<Product> products))
    {
        products = GetProductsFromDatabase();

        var cacheOptions = new MemoryCacheEntryOptions()
            .SetSlidingExpiration(TimeSpan.FromMinutes(5));

        _cache.Set("products", products, cacheOptions);
    }

    return Ok(products);
}

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4. Distributed Caching (Redis, SQL Server)

For multi-server environments, use distributed cache.

Common choice:

• Redis: Redis can store complex data types like Lists, arrays, Hash tables etc.

• Memcached: Simple text string store 

Example Setup with Redis

builder.Services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = "localhost:6379";
});

Then inject IDistributedCache.

Feature	Memcached	Redis
Distributed	Yes	Yes
Replication	No (basic)	Yes
Persistence	No	Yes
Data loss risk	Higher	Lower
Complexity	Simple	Advanced

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Which One Should You Use?

Scenario	Recommended
Cache full API response	OutputCache
Scale across multiple servers	Redis (Distributed Cache)
Cache DB results only	IMemoryCache
Browser/proxy caching	ResponseCache

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Best Practice Tips

• Cache only GET requests.
• Avoid caching user-specific data unless using VaryBy.
• Always define expiration.
• Invalidate cache on data update.
• Use distributed cache in production with multiple instances.

Output cache and Response Cache both stores whole response handled by middleware, only difference is storage location. 

Response Caching vs Output Caching

Feature	Response Caching	Output Caching
Where caching happens	Client / Proxy (browser, CDN)	Server (inside ASP.NET Core)
Middleware	UseResponseCaching()	UseOutputCache()
Actually stores response on server?	No	Yes
Performance benefit for server	Minimal	Significant
Best for	Public APIs	High-performance APIs
Introduced	Early ASP.NET Core versions	.NET 7