Content Delivery Networks
Bit the Chipmunk, AWS Expert published on
Hi there, fellow cloud builders! Bit here — your trusty chipmunk pal scurrying through the caching layers of AWS networking. Today we’re diving into one of my favorite acorns: Amazon CloudFront, the content delivery network (CDN) that keeps users happy and latency low.
If you’re studying for the AWS Advanced Networking Specialty (ANS-C01) exam, you’ll need to understand how CloudFront fits into global network design — when to use it, how to optimize it, and what advanced networking magic makes it hum.
Let’s crack open this CDN acorn together! 🌰
🧭 Overview
You’ll need to show that you can:
- Design scalable, secure architectures using CloudFront
- Optimize delivery for static, dynamic, and API-based content
- Integrate with AWS origins like S3, ALB, and API Gateway
- Enhance visibility and automate behavior using logs, metrics, and edge functions
The key takeaway? CloudFront is your edge network accelerator for HTTP and HTTPS traffic — improving performance, reliability, and security globally.
☁️ 1. Core Concepts of CloudFront
| Concept | What You Need to Know |
|---|---|
| Purpose | A global CDN that caches and accelerates content close to users. |
| Scope | Runs on AWS’s edge network with Regional Edge Caches (RECs) between origins and edges. |
| Origins | Common: S3, ALB, API Gateway, MediaPackage, or even private EC2 origins. |
| Protocols | Layer 7 (HTTP/HTTPS), supports static, dynamic, and API traffic. |
| Private Connectivity | For private ALB/EC2 origins, use CloudFront VPC Origins (AWS PrivateLink via an interface VPC endpoint under the hood). |
Bit’s Tip: When your origin lives in a private subnet, don’t open it to the public internet! Instead, use CloudFront VPC Origins to connect via PrivateLink and restrict the origin’s security group to CloudFront’s managed prefix list. It’s both faster and safer.
🧩 2. Design Patterns and Use Cases
a. Static Content Delivery
Pattern: CloudFront → S3 Origin
Key ideas:
- Cache assets globally (HTML, JS, images, video).
- Use Origin Access Control (OAC) instead of the old OAI.
- Add WAF and Shield for DDoS protection.
- Manage caching with Cache-Control headers and versioned file names (
logo.v4.png).
Bit’s Tip: If it’s static and global, CloudFront + S3 + OAC is your perfect nut.
b. Dynamic or Personalized Content
Pattern: CloudFront → ALB → EC2/ECS/EKS
Key ideas:
- CloudFront accelerates TLS handshakes even when caching isn’t used.
- Set Minimum TTL = 0 for real-time responses.
- Fine-tune caching using Cache-Control, Max-Age, and S-Maxage headers.
- Use Origin Groups for multi-region failover — health checks determine which origin is active.
- Configure Custom Error Responses (e.g., serve a static page from S3 on 503).
Bit’s Tip: “Dynamic” doesn’t mean “no caching.” Cache partial or API responses with smart TTLs!
c. API Acceleration
Pattern: CloudFront → API Gateway (edge-optimized or regional)
Key ideas:
- Edge-optimized APIs already use CloudFront.
- Regional APIs need a custom distribution.
- Cache
GETresponses; use query string or header whitelisting. - Protect APIs with WAF and Shield.
Bit’s Tip: API Gateway focuses on logic; CloudFront focuses on global speed.
d. Video and Large File Streaming
Pattern: CloudFront → S3 or MediaPackage
Key ideas:
- Supports HLS, DASH, CMAF streaming formats.
- Use signed URLs/cookies for paywalled or expiring access.
- Use RECs to keep frequently accessed segments close to viewers.
Bit’s Tip: Remember: S3 Transfer Acceleration = uploads, CloudFront = streaming.
e. Multi-Region Active-Active
Pattern: CloudFront → multiple ALBs (via Origin Groups or Lambda@Edge routing)
Key ideas:
- Failover within CloudFront is faster than DNS-based failover.
- Combine with Route 53 latency routing or Global Accelerator for ultimate resilience.
Bit’s Tip: Use Lambda@Edge or CloudFront Functions to route users by GeoIP, headers, or cookies.
🔐 3. Security and Access Control
| Feature | Description | Why It Matters |
|---|---|---|
| OAC (Origin Access Control) | Allows only CloudFront to reach S3. | Essential for exam—know how it replaces OAI. |
| PrivateLink Origins | Keeps ALB/EC2 origins private inside VPCs. | Prevents public exposure. |
| Signed URLs/Cookies | Time-limited or user-specific access. | Used for secure content delivery. |
| WAF Integration | Blocks SQLi, XSS, bots. | Common “defense-in-depth” question. |
| AWS Shield | DDoS protection (Standard = free; Advanced = SLA). | Understand scope differences. |
Bit’s Tip: Security at the edge is not optional—it’s baked into CloudFront’s fur.
⚙️ 4. Performance & Caching Optimizations
| Feature | What It Does |
|---|---|
| Regional Edge Caches | Intermediate layer reduces origin load and improves hit ratio. |
| Cache Behaviors | Define path-based rules (/api/*, /images/*). |
| Cache Keys | Control what makes an object unique in cache—by headers, cookies, query strings. |
| CloudFront Functions | Lightweight logic to adjust headers or cache keys (faster + cheaper than Lambda@Edge). |
| Persistent Connections | Keeps TLS and TCP sessions alive for reuse. |
| HTTP/2 & HTTP/3 | Reduce latency and handshake time. |
Bit’s Tip: Tweaking cache keys at the edge with CloudFront Functions is a frequent exam topic—great for personalization without flooding the origin.
🧰 5. Monitoring, Logging & Troubleshooting
Visibility matters! CloudFront integrates with several monitoring tools:
| Tool | Purpose |
|---|---|
| CloudWatch Metrics | Monitor cache hit ratio, origin latency, and error rates. |
| Standard Logs (S3) | Detailed access logs for offline analysis. |
| Real-Time Logs (Kinesis) | Stream request data within seconds for live analytics or alerting. |
| CloudWatch Alarms | Trigger notifications when error rates spike or hit ratio drops. |
| AWS WAF Logs | Capture blocked request details for security tuning. |
Bit’s Tip: Expect questions like: “How can you analyze requests within seconds for troubleshooting?” → CloudFront Real-Time Logs + Kinesis Data Stream.
💸 6. Cost Optimization
| Strategy | Why It Helps |
|---|---|
| Longer TTLs | Reduces origin requests and egress. |
| Price Classes | Limit edge coverage to reduce cost. |
| CloudFront Functions | Cheaper than Lambda@Edge for header manipulation. |
| Restrict Invalidations | > 1,000 paths/month = extra charge. |
Bit’s Tip: On exam day, “optimize cost” usually means extend TTLs or use fewer edge locations.
🌍 7. Comparing Edge Services
| Service | When to Use |
|---|---|
| CloudFront | HTTP/HTTPS acceleration + caching + WAF |
| Global Accelerator | TCP/UDP acceleration + static IPs (no caching) |
| Route 53 | DNS-based traffic steering |
| S3 Transfer Acceleration | Fast uploads to S3 only |
Bit’s Tip: Caching = CloudFront. Static IPs = Global Accelerator. DNS Routing = Route 53.
🧠 8. Common Exam Scenarios
Scenario 1:
Global website serving static + dynamic content needs low latency. ✅ CloudFront → ALB → EC2 with OAC, PrivateLink for private origin.
Scenario 2:
Private reports available for 24 hours only. ✅ CloudFront + Signed URLs + OAC.
Scenario 3:
Global API caching and DDoS protection. ✅ CloudFront + API Gateway + WAF.
Scenario 4:
UDP-based game backend. ❌ CloudFront (HTTP-only). ✅ Global Accelerator.
📚 Further Reading
- Amazon CloudFront Developer Guide
- Optimizing cache behavior and TTLs
- Using CloudFront with private origins via AWS PrivateLink
- Configuring CloudFront Functions
- CloudFront Real-Time Logs
- AWS WAF and Shield Integration with CloudFront
🐿️ Bit’s Final Nut
CloudFront isn’t just a CDN—it’s AWS’s edge platform for global performance, security, and resilience. Understand how it interacts with PrivateLink, cache keys, and Event-driven logs, and you’ll have the edge (pun totally intended) on your exam.
Stay cached, stay clever, and keep your packets speedy! 🌰💨