The most flexible self-hosted setup is Node Exporter → Prometheus → Alertmanager. Node Exporter exposes Linux CPU, memory, filesystem, and network metrics; Prometheus stores and evaluates those metrics; Alertmanager groups, silences, and delivers notifications. A practical alternative is Netdata, which combines collection, dashboards, and health alerts in one service.
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This guide shows how to install the components safely, create sustained CPU, memory, disk, network, and availability alerts, test delivery, and tune thresholds from your VPS baseline rather than arbitrary percentages.
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Understand what each component does
Monitoring becomes easier to troubleshoot when collection, evaluation, and notification are separate responsibilities.
| Component | Role | What you operate |
|---|---|---|
| Node Exporter | Reads Linux hardware and kernel statistics and exposes them as HTTP metrics, normally on port 9100. | A binary, service account, service-manager unit, and firewall rule. |
| Prometheus | Scrapes targets, stores time-series data, and evaluates PromQL alerting rules. | Scrape configuration, rule files, retention, and the Prometheus service. |
| Alertmanager | Groups related alerts, suppresses duplicates, handles silences and inhibition, and sends notifications. | Receivers, routing, grouping, and reloads. |
The official Node Exporter example scrapes localhost:9100 every 15 seconds. Typical series include node_filesystem_avail_bytes for available filesystem space and node_network_receive_bytes_total for cumulative received traffic. Prometheus evaluates whether a condition remains true; Alertmanager decides who should be notified and when.
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Prepare the VPS and lock down access
Choose where the monitoring services run
You can run all three components on the VPS being monitored, although a separate monitoring host is safer for multi-server deployments. If Prometheus runs elsewhere, Node Exporter’s port 9100 must be reachable from that Prometheus host but not from the public internet. Keep Prometheus and Alertmanager administrative endpoints on a private interface or behind authentication and network controls.
Create dedicated identities
Run Node Exporter, Prometheus, and Alertmanager as non-login service accounts rather than as root. Give each process read access only to the files it needs, and use a separate configuration directory with ownership restricted to the relevant account. Your distribution’s service manager (commonly systemd) should supervise the processes and restart them after a failure.
Set firewall boundaries
- Allow TCP 9100 only from the Prometheus server or private monitoring network.
- Allow Prometheus and Alertmanager web ports only from administrators and the systems that must query them.
- Do not expose administrative reload endpoints directly to the public internet.
- Record the private address and hostname of every monitored instance so alert messages identify the affected machine.
Install and verify Node Exporter
Obtain the correct binary
Download the official Node Exporter release that matches the VPS operating system and CPU architecture. Extract the static binary to a root-owned directory such as /usr/local/bin, and confirm that it executes before creating the service. Avoid copying a binary built for a different architecture; an immediate “Exec format error” usually indicates that mismatch.
Create a service account and unit
Create a dedicated node_exporter account without shell access. A systemd unit can follow this pattern (adjust paths to your distribution):
[Unit]
Description=Prometheus Node Exporter
After=network-online.target
[Service]
User=node_exporter
Group=node_exporter
ExecStart=/usr/local/bin/node_exporter
Restart=on-failure
[Install]
WantedBy=multi-user.targetSave the unit under the service manager’s unit directory, reload unit definitions, enable it at boot, and start it. Then inspect service status and logs. The process should listen on port 9100 without requiring root privileges.
Check the metrics endpoint locally
Before involving Prometheus, run:
curl http://localhost:9100/metricsA successful response is plain-text metrics containing names such as node_cpu_seconds_total, node_memory_MemAvailable_bytes, node_filesystem_avail_bytes, and node_network_receive_bytes_total. If the connection is refused, check the service status, listening sockets, and local firewall. If the endpoint works locally but not remotely, inspect the network rule and the address on which Node Exporter is listening.
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Review collectors before enabling extras
Node Exporter includes optional collectors. Some have high cardinality, long runtimes, or significant resource demands. Keep the default set initially; enable additional collectors one at a time and watch scrape duration and Prometheus resource use. An alerting system that consumes excessive CPU or delays scrapes can hide the failure it is meant to report.
Configure Prometheus to scrape the VPS
Add the minimal scrape job
In Prometheus’s configuration file, add a job for the exporter. The documented 15-second example is:
global:
scrape_interval: 15s
scrape_configs:
- job_name: node
static_configs:
- targets: ['localhost:9100']Use the private hostname or address instead of localhost when Prometheus is on another machine. Keep a stable job_name and target label so alert routes and dashboards remain understandable.
Validate before reloading
- Run Prometheus’s configuration-check command for your installed version against the edited file.
- Fix YAML indentation, duplicate keys, and file-permission errors before reloading.
- Reload Prometheus through the service manager or its configured reload mechanism.
- Open the targets view and confirm the Node Exporter target is UP.
- Query a simple series such as
node_filesystem_avail_bytesto verify that samples are arriving.
If a target is down, the up series for that target becomes zero. This is useful both for troubleshooting and for a direct exporter-availability alert.
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Every rule should have a descriptive alert name, a PromQL expression, a severity label, a for duration, and annotations containing a concise summary plus a remediation link or runbook reference. Use warning and critical severities for different operating responses. A short-lived burst should normally be recorded in a dashboard, not page an operator.
CPU saturation
Busy CPU is calculated from the rate of non-idle CPU time. This example fires when average busy time stays above 85 percent for five minutes:
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groups:
- name: linux-resource
rules:
- alert: HostCpuSaturation
expr: 100 * (1 - avg by (instance) (rate(node_cpu_seconds_total{mode='idle'}[5m]))) > 85
for: 5m
labels:
severity: warning
annotations:
summary: 'CPU saturation on {{ $labels.instance }}'
description: 'Average busy CPU has exceeded 85% for five minutes.'The threshold and five-minute window are starting points, not universal limits. A batch-processing VPS may routinely exceed 85 percent, while a latency-sensitive service may need an earlier warning. You can also compare load with the VPS core count; a load value that is harmless on many cores may saturate a single-core instance.
Memory pressure and swap
Alert on available memory, not merely memory reported as “used.” Linux uses otherwise idle RAM for cache, so an available-memory series better represents whether applications can obtain memory. A percentage expression can be built from node_memory_MemAvailable_bytes and node_memory_MemTotal_bytes:
- alert: HostLowMemory
expr: 100 * node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes < 10
for: 5m
labels:
severity: critical
annotations:
summary: 'Low available memory on {{ $labels.instance }}'
description: 'Available memory is below 10%; inspect processes, cache pressure, and swap.'Set the percentage from several days of normal measurements and your application’s behavior. On a VPS with little or no swap, a brief dip can precede an out-of-memory kill; on a server with active swap, sustained swap-in and swap-out activity can signal pressure even when a percentage threshold has not fired. Treat swap activity as a companion alert rather than assuming that any swap use is an emergency.
Filesystem capacity and read-only mounts
Use available bytes or available percentage from node_filesystem_avail_bytes and its size series. Exclude pseudo-filesystems and temporary mounts with label matchers appropriate to your host; otherwise virtual mounts can create noisy alerts.
- alert: HostFilesystemLow
expr: 100 * node_filesystem_avail_bytes{fstype!~'tmpfs|予seudo'} / node_filesystem_size_bytes{fstype!~'tmpfs|予seudo'} < 10
for: 10m
labels:
severity: warning
annotations:
summary: 'Low disk space on {{ $labels.instance }} {{ $labels.mountpoint }}'
description: 'Available filesystem space is below 10%; remove files or expand storage.'Replace the illustrative filesystem matcher with the actual pseudo-filesystem types reported by your exporter; do not copy an exclusion blindly. Include both instance and mountpoint in the annotation so the operator knows which volume is filling. Add a separate condition for a filesystem mounted read-only when your environment exposes a suitable metric, because a read-only root or data volume can break writes long before capacity is exhausted.
Network traffic and errors
Counter metrics must be converted to rates. The documented query pattern for received traffic is:
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rate(node_network_receive_bytes_total[1m])Apply the rate to the interface labels used on your VPS and alert on unusual traffic relative to the established baseline. Also monitor packet errors and drops when those series are available. A sudden traffic increase may indicate legitimate growth, a backup, or an attack, so route it initially as a warning and include the interface name in the annotation.
Exporter and service reachability
Use an availability rule for targets that Prometheus can no longer scrape:
- alert: HostExporterDown
expr: up{job='node'} == 0
for: 5m
labels:
severity: critical
annotations:
summary: 'Node Exporter is unreachable on {{ $labels.instance }}'
description: 'Prometheus has not successfully scraped the exporter for five minutes.'This catches a stopped exporter, a crashed VPS, a firewall change, and a broken route. Add application-specific health checks separately; an exporter being healthy does not prove that a web server, database, or queue is serving requests.
Connect Alertmanager to notifications
Define receivers and routing
Alertmanager receivers can deliver email, Slack, Telegram, Discord, webhooks, and other integrations. Store credentials outside world-readable configuration files where your deployment method supports it. Route by labels such as severity, and group by alertname, instance, or another label that keeps one incident together.
route:
receiver: default
group_by: ['alertname', 'instance']
group_wait: 30s
group_interval: 5m
repeat_interval: 4h
routes:
- matchers:
- severity='critical'
receiver: urgent
receivers:
- name: default
# Configure an email, chat, or webhook integration here.
- name: urgent
# Configure the urgent destination here.Use silences for planned maintenance and inhibition rules when one root failure would otherwise create a flood of dependent alerts. For example, suppress host-level symptoms while a confirmed host-down alert is active, but do not silence the host-down notification itself.
Reload and test delivery
- Validate the Alertmanager configuration with the version-matched configuration checker.
- Reload it by sending
SIGHUPor by posting to/-/reloadwhen that endpoint is enabled and protected. - Temporarily create a test rule with a condition you can trigger safely, or use a controlled maintenance target.
- Confirm that the notification arrives at the intended receiver, is grouped as expected, and contains the instance and remediation information.
- Restore the normal rule and verify that a resolved notification is delivered or recorded according to your receiver settings.
Choose Netdata when an integrated view matters more
Netdata is a credible alternative when rapid installation, an integrated dashboard, and preconfigured health alerts are more important than PromQL and centralized long-term analysis. Its Linux virtual-machine collector documents CPU, memory, disk I/O, and network utilization through cgroups, with alerts such as ten-minute CPU usage and RAM in use.
Netdata alert definitions distinguish chart-specific alarm: entries from reusable template: entries. Use a template when the same condition should apply consistently to multiple disks or interfaces, and a chart-specific alarm when one resource needs an exception. Choose Prometheus plus Node Exporter for PromQL, durable time-series analysis, multi-host aggregation, and a broad integration ecosystem; choose Netdata for a single integrated interface and less initial wiring. That is an architectural trade-off, not a claim that one product is universally better.
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Collect a baseline
Leave collection running for several days that include normal traffic, backups, deployments, and the busiest expected period. Record normal CPU busy time, available memory, swap activity, filesystem growth, and network rates. Then set warning thresholds before the point at which an operator must act, and critical thresholds where service impact is plausible.
Make alerts actionable
- State the affected instance and, for storage, the mountpoint.
- Include the measured condition and duration in the summary or description.
- Point to a runbook that explains the first safe checks and rollback steps.
- Use a warning for investigation and a critical severity for immediate response.
- Review alert frequency after every major workload, kernel, or storage change.
Control cardinality and scrape cost
Every additional label combination creates more time series. Keep optional collectors and high-cardinality dimensions disabled until you have a specific question they answer. Watch Prometheus memory use, scrape duration, and missed samples after each change.
Troubleshoot common failures
The target is down
Run curl http://localhost:9100/metrics on the VPS, inspect the Node Exporter service log, and verify that Prometheus is using the correct private address and port. If local access succeeds but the target remains down, check firewall rules, routing, and whether the exporter is bound only to loopback.
Rules never become firing
Evaluate the PromQL expression directly in Prometheus, confirm that the expected labels and metric names exist, and check that the rule file was loaded after validation. A for clause intentionally delays firing; verify that the condition remains true for the complete duration.
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Too many notifications arrive
Increase the duration for transient conditions, group related alerts in Alertmanager, add inhibition for dependent symptoms, and split warning from critical routes. Do not solve noise by silencing a recurring failure indefinitely; change the threshold or fix the underlying capacity issue.
Disk alerts point to the wrong volumes
Inspect the filesystem labels returned by Node Exporter, then refine matchers to exclude pseudo-filesystems and temporary mounts present on your VPS. Keep separate rules for persistent data volumes and ephemeral paths when their operational responses differ.
Quick Recap
Operational checklist
- Create dedicated, least-privilege service accounts.
- Install the architecture-matched Node Exporter release and run it under the host service manager.
- Restrict port 9100 and administrative endpoints with firewall and network controls.
- Verify
curl http://localhost:9100/metricsbefore configuring remote scraping. - Add the 15-second Prometheus scrape job and confirm the target is up.
- Create sustained CPU, memory, filesystem, network, and exporter-availability rules.
- Validate and reload Prometheus and Alertmanager configurations.
- Test both firing and resolved notifications.
- Base thresholds on several days of measurements and review them after workload changes.
- Audit optional collectors and scrape duration whenever monitoring scope expands.
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