Caching in ASP.NET Core — In-Memory, Distributed, Redis

Introduction

ShopNest product catalog under flash sale load needs caching — IMemoryCache for single server, Redis for distributed cache across multiple App Service instances.

After this article you will

• Apply cache-aside pattern for product lists
• Configure Redis IDistributedCache
• Invalidate cache on product updates
• Use output caching (.NET 8) on API endpoints
• Prevent cache stampede with locks

Prerequisites

• Article 47 — Background Services
• ShopNest API, EF Core, and DI from prior modules

Concept deep-dive

public async Task<ProductDetailDto?> GetProductAsync(int id, CancellationToken ct)
{
    var key = $"product:{id}";
    if (_cache.TryGetValue(key, out ProductDetailDto? cached))
        return cached;

    var product = await _db.Products.AsNoTracking()
        .ProjectTo<ProductDetailDto>(_mapper.ConfigurationProvider)
        .FirstOrDefaultAsync(p => p.Id == id, ct);
    if (product != null)
        _cache.Set(key, product, TimeSpan.FromMinutes(10));
    return product;
}

// Redis
builder.Services.AddStackExchangeRedisCache(options =>
    options.Configuration = config["Redis:Connection"]);

// Output caching — .NET 8
[OutputCache(Duration = 60, VaryByQueryKeys = new[] { "page", "categoryId" })]
[HttpGet]
public async Task<IActionResult> List() => Ok(await _service.GetPageAsync());

Stampede: use SemaphoreSlim or FusionCache library so only one thread repopulates cold cache.

Hands-on — ShopNest High-Traffic Product Catalog

1. Redis in Docker Compose for local ShopNest.
2. Cache-aside on GET product; Remove on PUT/DELETE.
3. OutputCache on product list API.
4. Load test before/after — document latency improvement.

Common errors & best practices

• Caching personalized data with public key — user A sees user B data.
• No TTL — stale prices after admin update.
• IMemoryCache in multi-instance production — each server different cache.

Interview questions

Q: Cache-aside?
A: App checks cache, on miss loads DB and sets cache.

Q: Cache invalidation?
A: Delete/update cache keys when source data changes — hardest part of caching.

Q: Output vs response caching?
A: Output caching (.NET 8) caches full endpoint result at server.

Summary

• Redis shares cache across ShopNest web farm
• Cache-aside + invalidation keeps catalog fresh
• Output caching speeds read-heavy list endpoints
• Prevent stampede on hot keys during sales

Previous: Background Services
Next: Health Checks

FAQ