Output Caching in ASP.NET Core .NET 8

Introduction

Output caching (.NET 8) caches entire endpoint responses — faster than manual IMemoryCache in controllers for ShopNest news and product list APIs.

After this article you will

• Use [OutputCache] attribute and profiles
• Vary cache by query, headers, user
• Invalidate with cache tags
• Distributed output cache with Redis
• Know when NOT to cache

Prerequisites

• Article 73 — Rate Limiting
• Articles 1–64 ShopNest foundations (MVC, EF Core, API, auth, deploy)

Architecture & design

builder.Services.AddOutputCache(options =>
{
    options.AddBasePolicy(b => b.Expire(TimeSpan.FromSeconds(30)));
    options.AddPolicy("NewsList", b => b
        .Expire(TimeSpan.FromMinutes(2))
        .SetVaryByQuery("page", "category")
        .Tag("news"));
});
app.UseOutputCache();

[OutputCache(PolicyName = "NewsList")]
[HttpGet("news")]
public async Task<IActionResult> GetNews() => Ok(await _news.GetPageAsync());

// Invalidate on publish
_outputCacheStore.EvictByTagAsync("news", ct);

Output vs Response caching: Output caching is server-side store with tag invalidation — more flexible than older response caching middleware.

Hands-on build guide — ShopNest High-Traffic News API

1. OutputCache on GET /api/v1/news.
2. Benchmark p95 before/after (Article 57 k6).
3. Evict tag on admin POST new article.
4. Redis distributed cache for farm.

Common pitfalls

• Caching authenticated personalized feed with public policy — data leak.
• No tag eviction — stale news until TTL expires.

Interview & portfolio questions

Q: Output vs IMemoryCache in action?
A: Output cache at middleware level — no controller code; automatic for GET.

Summary

• OutputCache simplifies high-traffic read endpoints
• Tags enable surgical invalidation on content publish
• Combine with rate limiting for public API protection

Previous: Rate Limiting
Next: .NET 9 New Features

FAQ