Multi‑CDN Strategy for Video Delivery: A Beginner’s Guide
In the evolving landscape of video streaming, a Multi-CDN (Content Delivery Network) strategy plays a crucial role in enhancing video delivery. This beginner’s guide will provide you with practical and actionable steps to understand, design, implement, monitor, and optimize a Multi-CDN framework. By addressing the challenges of single-point failures, this strategy ensures better performance and cost control for businesses aiming to improve viewer experience.
What is a CDN? Quick Primer
A CDN consists of a network of geographically distributed servers (edge servers/POPs) that cache content closer to viewers, enabling faster video start times and decreasing rebuffering. Here are some key concepts:
- Edge servers / POPs: Nodes that deliver cached content based on viewer location.
- Origin: The authoritative server where content is produced or packaged.
- Caching: Storing content closer to users to reduce load on the origin server.
- TTL and cache-control: Rules that determine how long cache items remain stored.
Key CDN Metrics for Video
- Latency: Includes DNS lookup time, TLS handshake, and first byte, affecting startup time.
- Throughput: The maximum bitrate a CDN can support for streaming.
- Cache hit ratio: A higher ratio results in lower origin egress and better performance.
- TLS handshake time: Can create delays in low-bandwidth scenarios.
For adaptive bitrate (ABR) streaming (HLS/DASH), consider metrics such as startup time, rebuffering ratio, playback bitrate, and play failures.
Why a Multi‑CDN Strategy for Video?
Business and Technical Drivers
Implementing a Multi-CDN strategy addresses several critical needs:
- Reliability and Redundancy: Avoid singular points of failure that can disrupt service.
- Performance: Optimize latency and throughput by selecting the best CDN based on geographical location or device.
- Cost Control: Balance egress costs and reserved capacity for optimized spending.
- Compliance: Ensure data residency regulations are met through appropriate traffic routing.
Typical Problems Solved by Multi‑CDN
- Bottlenecks during high-traffic live events.
- Poor performance in certain ISPs due to regional routing issues.
- High egress charges in specific areas, enabling routing to cost-effective providers.
Industry resources such as Bitmovin, Akamai, and Cloudflare can provide deeper insights into best practices.
How Multi‑CDN Works — Options & Architectures
Here’s a summary of common routing approaches for Multi-CDN strategies:
| Approach | How it Works | Pros | Cons |
|---|---|---|---|
| DNS Load Balancing (GeoDNS) | Resolves user requests to a CDN based on geographical rules | Simple and widely supported | Limited per-session control due to TTL caching |
| HTTP Redirect | Redirects user to a CDN URL | Quick failover, more control | Adds latency; requires player compliance |
| Client-Side Selection | Player selects CDN based on connection probes | Best QoE control and session optimization | More complex player integration required |
| Anycast/BGP | Routes based on ISP BGP paths | Network-level routing | Less flexible for session-specific steering |
Integration with Video Workflow
Ensure ABR manifests and DRM processes are compatible across CDNs to facilitate seamless switching.
Key Design Considerations for Video Multi‑CDN
- Define Target KPIs: Key performance indicators like startup time and rebuffering ratio help evaluate effectiveness.
- Caching Strategies: Maintain consistent asset URLs to enhance cacheability.
- TLS Management: Manage certificates effectively to streamline encryption processes.
- Monitoring: Regularly assess CDN performance with active probes and passive telemetry.
Implementation Steps — A Practical Roadmap
- Assess Needs and Set KPIs: Examples include startup time < 2s and availability of 99.95%.
- Select CDN Partners and Test Plan: Confirm POP coverage and peering strength.
- Choose Routing Model: DNS steering with HTTP redirects for quick setups.
- Build Testing Harness: Use synthetic probes and real user monitoring (RUM).
- Pilot, Iterate, Roll Out: Start small, validate KPIs, and adjust based on findings.
Monitoring, Measurement & Optimization
- Gather metrics from player SDKs and CDN logs for insights.
- Use dashboards to visualize performance against cost metrics.
Cost, Contracts & Commercial Considerations
- Negotiate pricing models based on expected traffic patterns, and watch for hidden charges.
Common Pitfalls & Troubleshooting
Avoid issues such as inconsistent asset URLs and long DNS TTLs, and use diagnostic tools to pinpoint rebuffering causes.
Short Case Example & Checklist
Mini Case: An OTT provider implements a Multi-CDN strategy for live streaming, optimizing their content delivery and ensuring continuity of performance.
Conclusion
In summary, a Multi-CDN strategy substantially enhances video streaming quality, availability, and cost efficiency. For beginners, starting small with thorough testing and gradual expansion is key. Prepare your infrastructure meticulously to ensure a smooth and effective deployment.
