Bypassing Cloudflare for True Origin Health Checks with Blackbox Exporter and CoreDNS

The approach described for bypassing Cloudflare's edge servers when performing external monitoring with Prometheus and Blackbox Exporter is an elegant solution to ensure accurate health checks on actual server endpoints. Here’s a summary of the key points:

Key Points

1. DNS Sidecar Approach:

   • Use CoreDNS or another DNS resolver as a sidecar process alongside your monitoring stack.
   • Configure this DNS resolver with custom hosts files that map domain names to internal IP addresses.

2. Separation of Concerns:

   • The Prometheus configuration remains simple, containing just the target endpoints (e.g., app.example.com).
   • The DNS resolver handles the mapping from these targets to their actual backend IPs.

3. Benefits:

   • Accuracy: Ensures that monitoring probes reach the real server and not intermediary services like Cloudflare.
   • Maintainability: Centralizes DNS override logic in one place, making it easier to manage changes.
   • Scalability: Allows for multiple Prometheus instances without duplicating configuration across hosts.

Detailed Implementation

1. CoreDNS Configuration:

   yaml
    
   1apiVersion: v1
   2kind: ConfigMap
   3metadata:

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