You only manage well what you measure
"The server was slow yesterday" isn't actionable. "Load average exceeded 8 between 2:00 and 2:20 p.m. with 92% I/O wait" is. Monitoring turns anecdotes into data.
Netdata: zero configuration, right away
bash <(curl -Ss https://my-netdata.io/kickstart.sh) and you get thousands of real-time metrics: CPU per core, IOPS per disk, disk latency, network connections. Expose it on localhost behind an authenticated reverse proxy, never publicly.
The four vital metrics
Load average vs vCores: above the vCore count continuously, you need more CPU. I/O wait: above 10%, storage is the bottleneck (not with us, but elsewhere…). Available RAM: if swap is working, add memory. Conntrack/connections: sudden spikes often signal scraping or a nascent attack.
Alerts, not dashboards
A beautiful dashboard nobody watches is useless. Configure alerts (Netdata → Discord/Slack/email) on the four vital metrics with strict thresholds, and only open dashboards to investigate.
External uptime
Internal monitoring can't see its own death. Add an external prober (self-hosted Uptime Kuma on another VPS, or a third-party service) checking your HTTP endpoints every 30 seconds from outside.