Glossary Guides

What Is a CDN

Learn what a CDN is, edge caching, performance benefits, DNS integration, SSL at the edge, and cache pitfalls.

By CheckDomainHealth Editorial Team Reviewed by Dionis Ceban Updated Jun 28, 2026 5 min read Beginner

Introduction

Instead of every visitor hitting your origin server directly, a CDN serves cached copies from many locations worldwide.

CDNs are common for static assets, full-site proxying (like Cloudflare), and media delivery.

Quick answer

A CDN (Content Delivery Network) caches and delivers website content from edge servers closer to visitors. CDNs improve speed, reduce origin load and often provide DDoS protection. DNS usually points to the CDN via CNAME or A records; SSL may be handled at the edge.

What it means

The origin server holds the real site. Edge servers cache responses and answer users from nearby locations when possible.

Caching — stores copies of pages and assets at edge
Edge servers — PoPs (points of presence) worldwide
DNS — often CNAME to CDN hostname
SSL — certificate may terminate at CDN edge
Cache purge — needed after content updates
Origin — your actual web server behind CDN

Where you see this:

Global websites needing faster load times
Static asset delivery (images, CSS, JS)
DDoS mitigation and WAF features
HTTPS proxy with CDN-managed certificates

Why this matters

CDN misconfiguration causes stale content, SSL loops, wrong caching of dynamic pages, and confusion between DNS issues vs cache issues during troubleshooting.

How to check it

Check DNS for CNAME or A records pointing to CDN.
Run Website Status Checker and note CDN response headers.
Use HTTP Header Checker to see cache and server headers.
Verify SSL mode matches origin HTTPS support.
Purge CDN cache after deployments and retest.

Check website via CDN

Use Website Status Checker to test response codes and whether CDN or origin serves content.

Run Website Status Check →

Common mistakes

Caching private or dynamic pages

High

Logged-in or cart pages served to wrong users.

Next step: Set cache rules to bypass sensitive URLs.

CDN SSL mode mismatch with origin

High

Flexible SSL causes redirect loops or insecure origin connections.

Next step: Use Full (strict) when origin has valid HTTPS.

Old content served from cache

Medium

Changes not visible after deploy.

Next step: Purge cache or lower edge TTL for updated assets.

DNS still points to old origin

Medium

CDN bypassed or wrong traffic path.

Next step: Update DNS to CDN targets per provider docs.

Blaming DNS when CDN cache is stale

Low

DNS correct but edge serves outdated response.

Next step: Purge CDN before further DNS changes.

Example

CDN DNS example

www.example.com CNAME example.cdnprovider.net

; Visitor → nearest edge server → origin (if not cached)

Frequently asked questions

Does a CDN replace web hosting?

No. You still need an origin server. CDN caches and proxies in front of it.

Can CDN cause redirect loops?

Yes, especially with Flexible SSL when origin forces HTTPS.

How do I clear CDN cache?

Use your CDN dashboard purge or API after content changes.

Is CDN the same as DNS?

No. DNS routes names to services. CDN caches and delivers content from edge locations.

Use these free tools to verify your configuration after applying changes.

Website Status Checker DNS Lookup SSL Checker HTTP Header Checker

Need help applying this fix?

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