VPS Sudden Slowness and DNS Timeout Issue Resolution

HTTP and HTTPS requests to external domains from the VPS take approximately 15 to 20 seconds to complete, while localhost requests respond instantly.

Symptoms
curl http://127.0.0.1 responds normally
curl https://domain.com takes around 20 seconds
dig queries time out against 127.0.0.53
systemd resolved logs show degraded feature set warnings

Cause
The issue is not related to web services, CPU load, or an attack.

The VPS was using provider DNS servers that became slow or unstable. systemd resolved attempted UDP and TCP fallbacks repeatedly, causing significant delay for every DNS lookup.

Resolution

1. Configure public DNS

Add the following to /etc/systemd/resolved.conf

DNS=1.1.1.1 8.8.8.8

2. Remove provider DNS from netplan

Edit /etc/netplan/50 cloud init.yaml and update the nameservers section to

addresses
1.1.1.1
8.8.8.8

3. Apply configuration

netplan apply
systemctl restart systemd resolved

Verification

Run resolvectl status and confirm that both global and interface DNS servers show only 1.1.1.1 and 8.8.8.8.

The issue was caused by upstream provider DNS instability. After switching to public DNS servers, the latency was completely resolved.