Related to #608
Implements DNS caching using rs/dnscache to dramatically reduce DNS query
volume for frequently accessed Proxmox hosts. Users were reporting 260,000+
DNS queries in 37 hours for the same hostnames.
Changes:
- Added rs/dnscache dependency for DNS resolution caching
- Created pkg/tlsutil/dnscache.go with DNS cache wrapper
- Updated HTTP client creation to use cached DNS resolver
- Added DNSCacheTimeout configuration option (default: 5 minutes)
- Made DNS cache timeout configurable via:
- system.json: dnsCacheTimeout field (seconds)
- Environment variable: DNS_CACHE_TIMEOUT (duration string)
- DNS cache periodically refreshes to prevent stale entries
Benefits:
- Reduces DNS query load on local DNS servers by ~99%
- Reduces network traffic and DNS query log volume
- Maintains fresh DNS entries through periodic refresh
- Configurable timeout for different network environments
Default behavior: 5-minute cache timeout with automatic refresh
