Domain Name System (DNS)
DNS is the phone book of the internet. It turns a name like sdprimer.com into an IP address that machines can use. Each time a user types a URL, a DNS lookup happens before any of your code runs.
DNS Record Types
| Record | Purpose | Example |
|---|---|---|
| A | Maps domain to IPv4 address | sdprimer.com → 93.184.216.34 |
| AAAA | Maps domain to IPv6 address | sdprimer.com → 2001:db8::1 |
| CNAME | Alias to another domain | www.sdprimer.com → sdprimer.com |
| MX | Mail server routing | sdprimer.com → mail.sdprimer.com |
| NS | Delegates to authoritative nameserver | sdprimer.com → ns1.provider.com |
| TXT | Arbitrary text (verification, SPF) | v=spf1 include:_spf.google.com |
DNS as a Load Distribution Tool
DNS is not only name resolution. It is your first chance to spread traffic. Managed DNS services like Route 53, Cloudflare DNS, or Google Cloud DNS offer:
- Weighted routing: Send 90% of traffic to your primary and 10% to a canary deployment.
- Latency-based routing: Direct users to the geographically closest data center.
- Failover routing: Automatically redirect traffic when health checks detect an outage.
- Geolocation routing: Route users based on their country or region (useful for compliance or localization).
Content Delivery Networks (CDN)
A CDN is a globally distributed network of edge servers that cache and serve content close to your users. Instead of every request traveling to your origin server (which might be in a single region), the CDN serves static assets (images, CSS, JavaScript, videos) from the nearest edge node.
Push CDN vs Pull CDN
You explicitly upload content to the CDN. You control exactly what gets cached and when it is updated.
- Best for: content that changes infrequently
- Pro: full control over cache contents
- Con: you manage upload + invalidation
CDN fetches content from your origin on the first request, then caches it. Subsequent requests are served from cache until TTL expires.
- Best for: high-traffic sites with diverse content
- Pro: zero config, lazy caching
- Con: first request is slow (cache miss)
Most modern CDNs (Cloudflare, Fastly, CloudFront) operate as pull CDNs by default, with the ability to push/preload specific assets when needed. This hybrid approach gives you the simplicity of pull with the control of push where it matters.
What CDNs Actually Improve
- Latency: Serving from a node 50ms away vs 200ms away is a massive UX difference, especially on mobile.
- Origin load: Your servers handle fewer requests. Most of your traffic is static assets that the CDN absorbs entirely.
- Availability: If your origin goes down briefly, cached content at the edge can still serve users.
- DDoS protection: CDN edge networks are designed to absorb large traffic spikes and malicious floods.