Web Server Caching

🖥️ Web Server Caching – No-Nonsense Explanation

Web server caching means storing generated responses (like HTML, JSON, etc.) on the server itself so future requests can be served faster without redoing the same work (like hitting the database or rendering templates).

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⚙️ How It Works

When a request hits your web server:

1. Without caching:

   • Request → Web server → App logic → DB → Render response → Return to client.

2. With caching:

   • First request: Goes through the full process and stores the result in a cache.

   • Next request: Web server checks cache first → If found, it returns cached response instantly.

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🧠 Types of Web Server Caching

Type	What it Caches	Where
Page Caching	Full HTML pages	Server memory/disk
Fragment Caching	Parts of a page (e.g., sidebar)	App level or templating engine
Object Caching	Data like DB results or API responses	Redis/Memcached
Reverse Proxy Caching	Sits in front (e.g., Nginx) and caches responses	Edge or server-side

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📍 Where It’s Used

• Nginx/Apache: Reverse proxy cache.

• Node.js/Express: In-memory or Redis caching.

• Django/Rails/Laravel: Use template fragment and view caching.

• Spring Boot: Can cache method results or HTTP responses.

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🧾 Example (Nginx Reverse Proxy Caching)

location / {
    proxy_pass http://app;
    proxy_cache my_cache;
    proxy_cache_valid 200 1h;
}

• Stores 200 OK responses for 1 hour.

• Next time the same URL is hit → Served directly from cache.

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🧼 Cache Invalidation

When cached data gets old or changes, you need to invalidate it:

• Time-based (Cache-Control: max-age=60)

• Manual (purge by URL or key)

• Trigger-based (purge when DB changes or on content update)

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✅ Benefits

• ⚡ Faster response time

• 🔄 Lower backend/database load

• 🔒 Can isolate and protect backend from spikes

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❗ Risks & Downsides

• 🧊 Stale content if not invalidated properly

• 🔁 More complex cache-control logic

• 🔓 May cache sensitive data if not configured carefully

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🧪 Real-World Example

You run a news site:

• Home page is rebuilt every 5 minutes.

• Instead of hitting DB and rendering template every time, the web server serves the cached HTML to every visitor.

• Huge speed gain and reduced backend cost.