Building Nagios 4 from source on Debian to monitor 75 hosts and 130 services: implementing custom checks for TCP services, DNS zones, XMPP, Tor, HTTP/HTTPS with cert expiry, plus SMS alerts via nagios-twilio and enhanced email with mtr output.
Configuring MikroTik hairpin NAT to access external IPs from internal network: implementing dst-nat and masquerade rules to route traffic destined for public IP back to internal reverse proxy when DNS returns external address.
Rewriting ipquail.com in Go using pilu/traffic router: replacing SSI/Apache hacks with proper API endpoints for IP/PTR lookups, nginx reverse proxy handling IPv4/IPv6 termination, and JSON response formatting.
Monitoring Tor hidden services with Nagios using torsocks: creating check_commands for HTTP/SSH/TCP over Tor, tracking onion availability/performance, and publishing monion repository with sample configs for .onion monitoring.
Implementing IPv6 monitoring in Nagios: creating dual-stack service checks with -4/-6 flags, defining custom _ADDRESS4/_ADDRESS6 variables for DNS independence, and navigating IPv4-only plugin limitations like check_icmp.
