CDN Resilience Checklist: 8 Things to Test Before You Need Them
Most CDN resilience plans look solid on paper and untested in practice. The gap between "we have failover configured" and "we know our failover works" is usually only discovered during a real outage — which is the worst possible time to find out. Here are eight things worth verifying before that happens.
01 Application-level health checks, not just pings
A server can respond to a ping while the application behind it is broken. Health checks should validate the actual user-facing behavior — an HTTP request to a real endpoint, a valid response code, and ideally a lightweight check of a critical dependency — not just basic reachability.
02 Multiple monitoring locations
A single monitoring location can mistake its own regional network blip for a target failure. Distributed checkers — probing from several geographies — reduce false positives and make failure detection something you can actually trust to trigger real action.
03 A tested, not assumed, failover path
Failover systems that have never been exercised under real conditions are unreliable by default, whether or not the configuration looks correct. Regular failover drills — deliberately simulating a CDN outage in a controlled way — are the only reliable way to know the switch actually works end to end.
04 DNS TTL tuned for failover, not left at default
If you're relying on DNS-based failover anywhere in your stack, check the TTL on those specific records. Defaults inherited from unrelated records (an hour, or more) can mean your "automatic" failover still takes far longer than expected to reach real users.
05 Failback behavior that doesn't cause a second incident
A failover system that correctly detects an outage and reroutes traffic can still cause a new problem on recovery, if it sends 100% of traffic back to a provider immediately after it's marked healthy. Gradual, incremental traffic restoration avoids overwhelming a system that's still stabilizing.
06 Hysteresis to prevent flapping
Failover that triggers too easily causes repeated switching between providers, which is often more disruptive to users than a single clean outage. Require sustained failure — and sustained health — over a defined window before switching in either direction.
07 Monitoring above the application layer
Some of the hardest incidents to diagnose are ones where your own infrastructure looks completely healthy — CPU normal, no application errors — but a routing or edge-network failure at your CDN provider means users still can't connect. External reachability monitoring, independent of your own servers, catches this category of failure that internal telemetry misses entirely.
08 A real second provider, not just a backup configuration
Failover only helps if there's somewhere healthy to fail over to. A backup pointing at infrastructure from the same provider doesn't protect against a provider-wide incident — only a genuinely separate CDN does.
Continuuly continuously runs these checks across multiple CDN providers and handles the detection, failover, and gradual recovery automatically — as an out-of-band control plane you don't have to build and maintain yourself. See how it works →