Why use more than one
Relying on a single CDN means a single point of failure and one provider's geographic strengths. A multi CDN setup routes traffic across two or more providers to gain resilience, broader reach, and pricing leverage.
How routing decides
A steering layer picks which CDN serves each request. Common signals include:
- Availability so a failing CDN is removed quickly.
- Performance from real user measurements per region.
- Cost to favor a cheaper provider when quality is similar.
Steering mechanisms
Steering often works through DNS, returning the chosen CDN's hostname, or through a routing layer that load balances across providers. Real user monitoring feeds the decision so it tracks actual conditions, not just static rules.
The hidden costs
Multi CDN adds complexity: cache hit ratios drop because each provider warms its caches separately, purges must fan out to all providers, and configuration must stay in sync. The payoff is no single provider outage taking you down, plus the ability to shift traffic for performance or price.
Key idea
Multi CDN steers traffic across providers by availability, performance, and cost for resilience and leverage, at the cost of split caches and synced configuration.