CDN vs. Caching: Key Differences and How They Work Together

Many WordPress users confuse CDN (Content Delivery Network) and caching, thinking they do the same thing. While both improve website performance, they work differently. Let’s break it down.

Explanation:

User’s Browser: Initiates a request for a WordPress page.
CDN Edge Server: The request first hits the CDN closest to the user.
- Cache HIT: If the CDN has the requested content cached, it serves it immediately, reducing load time.
- Cache MISS: If not cached, the CDN forwards the request to your origin server.
Web Server (Hosting WordPress):
- Page Caching Layer: Checks if a cached version of the page exists.
  - If cached: Serves the cached page.
  - If not cached: Proceeds to generate the page dynamically.
    - WordPress Core: Processes the request.
    - Database Queries: Retrieves necessary data.
    - Generate HTML Content: Combines data with templates to create the final page.
Response Back to CDN: The generated content is sent back to the CDN.
CDN Caches Content: The CDN stores the content for future requests, improving load times for subsequent users.
User’s Browser Receives Content: The final content is delivered to the user’s browser.

1. What is Caching?

Caching stores temporary copies of your website’s files (HTML, CSS, JS, images) to reduce server load and speed up page delivery.

How Caching Works:

When a user visits your site, the server generates the page dynamically (PHP + database queries).
A cache plugin (like WP Rocket, W3 Total Cache) saves a static version of that page.
The next visitor gets the pre-saved cached version, skipping PHP/database processing.

Types of Caching:

✔ Browser Caching – Stores files on the user’s device.
✔ Server-Side Caching – Stores HTML pages on your hosting server.
✔ Object Caching – Speeds up database queries (Redis, Memcached).

When to Use Caching?

Every WordPress site should use caching.
Best for reducing CPU usage and speeding up repeat visits.

2. What is a CDN?

A CDN (Content Delivery Network) is a network of global servers that deliver static files (images, CSS, JS) from the closest location to the user.

How a CDN Works:

Your main server hosts the website.
A CDN copies static files to multiple edge servers worldwide.
When a user visits, the CDN serves files from the nearest server, reducing latency.

When to Use a CDN?

If your audience is globally distributed.
To offload bandwidth from your main server.
To protect against DDoS attacks (many CDNs include security).

Key Differences Between CDN and Caching

Feature	Caching	CDN
What it stores	Full HTML pages, database queries	Static files (images, CSS, JS)
Where it’s stored	User’s browser or your server	Global edge servers
Main purpose	Reduce server processing	Reduce latency & bandwidth
Works best for	Repeat visitors, logged-in users	Global visitors, static assets
Example tools	WP Rocket, LiteSpeed Cache	Cloudflare, BunnyCDN

How CDN and Caching Work Together

✅ Step 1: A user visits your site.
✅ Step 2: Your server cache delivers a pre-generated HTML page.
✅ Step 3: The CDN serves images, CSS, and JS from the nearest edge server.
✅ Result: Faster load times + less server strain.

Example Scenario:

Without Caching & CDN:
- Every visit triggers PHP/database work.
- Files load slowly from a single server (e.g., USA → Australia = high latency).
With Caching & CDN:
- Returning visitors get cached HTML.
- Static files load from a local CDN server (e.g., Sydney edge server for AU users).

Common Misconceptions

❌ “A CDN replaces caching.” → No, they complement each other.
❌ “Caching is only for static sites.” → Even dynamic sites (WooCommerce) benefit from object caching.
❌ “A CDN speeds up my admin area.” → CDNs usually don’t cache /wp-admin/.

Which One Do You Need?

Use Caching If:
- Your site is slow due to high server load.
- You have mostly local visitors.
Use a CDN If:
- Your audience is global.
- You want to offload bandwidth and improve image loading.

Best Practice: Use both for maximum speed!