Secure Custom Domain Setup for Client Status Pages Using CNAME, Certbot and Go Instead of ACME On-Demand
A detailed case study describes how a monitoring service implemented white-label status pages on customer domains without relying on ACME on-demand certificate issuance. The approach uses pre-validated domains stored in a database, background DNS checks via CNAME or A-record matching, and a root helper script running on a systemd timer to handle certbot issuance and nginx configuration. Key design choices separate privileges so the Go application never touches certificates or nginx directly, while loopback endpoints are protected against proxy header spoofing. The solution explicitly addresses risks such as DoS through malicious Host headers exhausting Let's Encrypt rate limits, private key exposure, and first-visitor latency during TLS handshakes. Hysteresis in DNS status prevents temporary resolution glitches from disabling active customer pages. The entire implementation stays under a few hundred lines of code and runs reliably on a single server with nginx in front of the Go application.
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