IT Operations
Server Monitoring Tools: What to Use
The server monitoring tools teams actually run — open source and commercial — what each measures, where each breaks down, and how to pick one.
A server that fails quietly is worse than one that fails loudly. Server monitoring exists so the failure is loud — to you, before it is loud to your customers.
Basics
What server monitoring covers
Server monitoring watches the machines your services run on — resources, availability, processes, logs and real request paths — and alerts the right person when something degrades. It is a different job from watching switches and links; if network gear is your bigger worry, start with network monitoring tools and read this alongside it.
- Resource metrics — CPU, memory, disk space, disk I/O, network throughput
- Availability — is the host up, is the service listening, is the port answering
- Service and process state — did nginx, PostgreSQL or a queue worker stop
- Logs — errors and events, ideally centralised so you can correlate across hosts
- Application-level checks — a real HTTP request that exercises the app, not just a ping
- Alerting — thresholds, escalation and on-call routing
- History — trends over weeks, so you can size capacity instead of guessing
Open source
Open-source server monitoring tools
Open-source monitoring is genuinely production-grade — several of these run estates of thousands of hosts. The trade is always the same: no licence fee, real engineering time. Choose one of these if someone on the team will own it.
Zabbix
Zabbix is the most complete free monitoring system: agents for deep host metrics, SNMP and agentless checks for everything else, auto-discovery, templates for common platforms, flexible triggers and alerting, and dashboards — all in one product that scales to thousands of hosts.
Strengths: breadth with no licence cost; one tool can cover servers, network gear and services; mature templating and a large community. Limits: the initial setup effort is real — database sizing, housekeeping tuning and template curation are on you — and the UI, though improved, carries its depth. Who it fits: teams with mixed infrastructure and an engineer willing to own the deployment. Pricing: free and open source; the vendor sells optional support and services.
Prometheus + Grafana
Prometheus is the de facto metrics standard for modern infrastructure and Kubernetes: a pull-based time-series database scraping exporters on your hosts and services, with alerting via Alertmanager and dashboards in Grafana.
Strengths: superb time-series model and query language (PromQL), first-class Kubernetes integration, huge exporter ecosystem, and Grafana dashboards that have become the industry's shared language. Limits: it is a metrics toolkit, not a turnkey monitoring product — long-term storage, alert routing discipline and dashboard curation are assembly work, and classic SNMP hardware is not its strength. Who it fits: container and cloud-native estates with engineering capacity. Pricing: free and open source; managed and enterprise offerings from various vendors are separate.
Nagios Core
Nagios Core is the venerable check-and-alert engine: host and service checks run through plugins — locally, over SSH, or via agents such as NRPE — with state-based alerting and escalation.
Strengths: extreme extensibility — if you can script a check, Nagios can run it — plus decades of plugins and operational lore. Limits: configuration is file-based and manual, the UI is dated, and per-second metrics and modern dashboards are not what it does; many teams pair or replace it with newer stacks. Who it fits: teams that value stability and scriptability over polish, or that already run it well. Pricing: free and open source; Nagios XI is the vendor's commercial product.
Netdata
Netdata gives you beautiful per-second metrics on a host within minutes of installing its agent — thousands of metrics auto-discovered, no configuration, rendered in a live dashboard.
Strengths: unmatched setup-to-value time; the per-second granularity is genuinely useful when you are debugging a misbehaving host right now. Limits: it is strongest as a per-host lens; as a central, long-retention system of record for a whole estate it is less established, so many teams run it alongside a fleet-level tool rather than instead of one. Who it fits: anyone troubleshooting individual Linux hosts, and small estates that want visibility without a monitoring project. Pricing: open-source agent; the vendor's cloud offering has free and paid tiers — published price varies, check vendor.
Checkmk
Checkmk is a strong middle ground: agent-based monitoring with broad platform coverage, automatic service discovery, and far less manual configuration than Nagios, whose heritage it shares.
Strengths: quick to get broad coverage — the agent discovers what runs on a host and monitors it with sensible defaults; scales well; a free edition exists. Limits: the free Raw edition trails the commercial editions in features and support, and the interface takes some learning. Who it fits: mid-size teams that want Nagios-class coverage without Nagios-class configuration effort. Pricing: free Raw edition; commercial editions priced by services monitored — published price varies, check vendor.
Commercial
Commercial server monitoring tools
Commercial tools mostly sell time: faster deployment, hosted infrastructure, supported upgrades and someone to call. The pricing models differ sharply — per host, per sensor, or usage-based — so model the bill at your projected scale before comparing features.
Datadog
Datadog is the broadest SaaS observability platform: an agent on each host feeds infrastructure metrics, with APM, log management, synthetics and dozens of product modules layered on top, and integrations for practically everything.
Strengths: extremely capable across infrastructure, APM and logs in one place; excellent dashboards; near-zero infrastructure to run yourself. Limits: usage-based pricing can escalate quickly at scale — hosts, custom metrics, log volume and each product module all meter separately, so bills need active management. Who it fits: cloud-first teams that want depth across the stack and will govern usage. Pricing: per-host and usage-based subscription — published price varies, check vendor.
New Relic
New Relic comes at monitoring from the application side: strong APM — transactions, traces, code paths — with infrastructure monitoring included in the same agent-and-SaaS model.
Strengths: application performance visibility is the core competence, and having infrastructure in the same platform means you can walk from a slow transaction to the host it ran on. Limits: if you only need host-level monitoring, an APM-first platform is more than the job requires; pricing is usage-and-seat based and needs the same governance as any SaaS observability bill. Who it fits: teams whose primary question is 'why is the application slow', with infrastructure as context. Pricing: usage-based (data ingest and users) — published price varies, check vendor.
SolarWinds SAM
SolarWinds Server & Application Monitor is the classic on-premise choice for Windows-heavy estates: deep coverage of Windows servers and application stacks (IIS, SQL Server, Exchange, Active Directory) with hundreds of application templates, collected mostly agentlessly over WMI and SNMP with optional agents.
Strengths: depth on Windows and enterprise application servers; sits alongside SolarWinds' network products for a combined view. Limits: priced and built for larger estates, runs on infrastructure you host, and is not the natural pick for containerised or cloud-native workloads. Who it fits: mid-size and large Windows-centric IT departments. Pricing: licensed by monitored nodes — published price varies, check vendor.
ManageEngine Applications Manager
ManageEngine Applications Manager covers servers, application servers, databases and cloud services at mid-market pricing, and is common in India alongside the rest of the ManageEngine suite.
Strengths: broad coverage — servers, databases, web servers, virtualisation and cloud in one product — at pricing aimed below the enterprise tier. Limits: as with most broad suites, depth varies by monitor type, so verify the specific stacks you run; the interface shows the product's breadth. Who it fits: mid-market teams, especially those already using ManageEngine products. Pricing: by monitored instances and edition — published price varies, check vendor.
PRTG
PRTG (Paessler) monitors through sensors — one sensor per metric or check, deployed from a central core server and remote probes, mostly agentlessly via WMI, SNMP and standard protocols.
Strengths: quick to deploy, approachable interface, and one product covers servers and network devices — a genuine advantage for small teams monitoring both. Limits: the sensor-based licence means cost rises with the number of things you measure, and large estates can hit sensor-count and architecture ceilings. Who it fits: small and mid-size estates that want fast, combined server-and-network coverage. Pricing: licensed by sensor count — published price varies, check vendor.
At a glance
Server monitoring tools compared
The table condenses the tools above. Licence terms and editions change, so verify the row you shortlist against the vendor's current documentation.
Server monitoring tools at a glance
| Tool | Licence | Agent model | Best for |
|---|---|---|---|
| Zabbix | Free, open source | Agent, SNMP and agentless checks | Complete free monitoring across mixed estates |
| Prometheus + Grafana | Free, open source | Pull-based scraping of exporters | Containers, Kubernetes and cloud-native services |
| Nagios Core | Free, open source | Plugin checks (NRPE, SSH) | Scriptable checks and extreme extensibility |
| Netdata | Open-source agent | Per-host agent, per-second metrics | Deep troubleshooting on individual hosts |
| Checkmk | Free edition + commercial | Agent-based with auto-discovery | Broad coverage without Nagios-level configuration |
| Datadog | Commercial SaaS | Agent per host | Infrastructure, APM and logs in one platform |
| New Relic | Commercial SaaS | Agent per host | APM-first teams with infrastructure as context |
| SolarWinds SAM | Commercial | Mostly agentless (WMI/SNMP), optional agent | Windows and application-server estates |
| ManageEngine Applications Manager | Commercial | Mostly agentless | Mid-market breadth across servers and databases |
| PRTG (Paessler) | Commercial | Sensors via core server and probes | Quick combined server-and-network coverage |
How to choose
Four questions settle most shortlists: how rich does per-host data need to be, how long must history be kept, how disciplined is the alerting, and what will the bill look like at next year's scale — not today's.
- Agent or agentless — agents give far richer data; agentless is easier where you cannot install software.
- Check retention: how long are raw metrics kept before roll-up? This decides whether you can investigate last month's incident.
- Check alert routing and de-duplication — a monitoring tool that pages you fifty times for one outage will be muted, and then it is useless.
- Beware usage-based pricing if your host count fluctuates; model the bill at your projected scale, not today's.
- If you also need patching, remote access and automation on the same machines, an RMM platform may cover monitoring as part of the bundle.
- Ask whether you need a separate tool at all, or whether server monitoring inside your existing IT platform — where the asset, the ticket and the patch status already live — is enough.
Infronest
Conclusion
Infronest includes agent-based server monitoring — health, CPU, memory, disk, services, logs and uptime history — in the same tenant-isolated workspace as network monitoring, IT assets, patching and helpdesk. An alert opens a ticket against the asset it came from, with its patch and ownership history already attached.
Start a 14-day free trial at infronest.com — no credit card required.
Frequently Asked Questions
- What is the best free server monitoring tool?
- Zabbix for a complete free monitoring system across mixed infrastructure, or Prometheus with Grafana if your estate is container and cloud-native. Netdata is excellent for deep per-second visibility on individual hosts, and Checkmk's free edition is a strong middle ground if Nagios-style configuration puts you off.
- What should you monitor on a server?
- At minimum: CPU, memory, disk space and disk I/O, network throughput, host availability, the state of critical services, and application-level checks that exercise the real request path. Add log collection so you can investigate rather than guess.
- How is server monitoring different from APM?
- Server monitoring watches the machine — resources, services and availability. APM (application performance monitoring) watches code paths, transactions and dependencies inside the application. A healthy server can still host a slow application, which is why larger teams run both.
- Is agent-based or agentless server monitoring better?
- Agents give far richer data — per-process detail, logs, service state and application checks — and work for hosts outside your network. Agentless collection over WMI, SSH or SNMP is easier where you cannot install software, such as appliances or tightly controlled servers. Most estates end up with agents on the servers that matter and agentless checks for the rest.
- How much does server monitoring software cost?
- Open-source options (Zabbix, Prometheus, Nagios Core) are free but cost setup and maintenance time. Commercial tools price per host, per sensor or by usage (data ingested), typically as an annual subscription. Published prices vary by vendor and scale — model the bill at your projected host count, and watch usage-based models if your estate fluctuates.
- Can one tool monitor both Windows and Linux servers?
- Yes — Zabbix, Checkmk, Datadog, PRTG and most modern platforms cover both with the same console, though depth differs: verify Windows service and event-log coverage and Linux process and log coverage specifically. Tools with a Windows heritage, such as SolarWinds SAM, are deepest on Windows application stacks.
- How long should you keep server monitoring data?
- Keep raw, fine-grained metrics for at least a few weeks so you can investigate incidents after the fact, and rolled-up trends for a year or more so capacity planning rests on data rather than memory. Check each tool's retention and roll-up behaviour before committing — it varies widely and is painful to discover during an investigation.