Having used both Munin and Nagios in production environments for Linux server monitoring (specifically for service availability and functional link checks), I'll break down their distinct approaches:

• Nagios: Specializes in alert-driven monitoring with active checks (HTTP, SSH, disk space thresholds)
• Munin: Focuses on trend analysis through passive metric collection (CPU, memory, network trends)

Here's how to make them work together using Nagios' check_munin plugin:

# Install check_munin plugin
wget https://exchange.nagios.org/components/com_mtree/attachment.php?link_id=3489&cf_id=24 -O check_munin
chmod +x check_munin
mv check_munin /usr/lib/nagios/plugins/

# Nagios service definition example
define service {
    use                 generic-service
    host_name           web-server-01
    service_description Munin Disk Usage
    check_command       check_munin!diskstats!--warning 90%--critical 95%
}

Use Nagios when:

• You need immediate SMS/email alerts for service outages
• Require complex dependency chains (e.g., "don't alert on web servers if database is down")

Use Munin when:

• Capacity planning through historical data (e.g., "when will we need more storage?")
• Quick visualization of correlated metrics (network traffic vs. disk I/O)

For those wanting to minimize configuration overhead while keeping Nagios' alerting:

# On monitored node (munin-node + NRPE):
apt install munin-node nagios-nrpe-server

# Sample NRPE config snippet:
command[check_munin_disk]=/usr/lib/nagios/plugins/check_munin --plugin diskstats --warning 85% --critical 95%

Having used both tools extensively in production environments, I can state that Munin and Nagios serve fundamentally different purposes in server monitoring:

// Nagios configuration example (service check)
define service {
    host_name               linux-server-01
    service_description     HTTP Check
    check_command           check_http
    max_check_attempts      3
    normal_check_interval   5
    retry_check_interval    1
}

Meanwhile, Munin focuses on trend visualization through RRDtool:

# Example Munin plugin (memory usage)
[memory]
user root
env.type linux
env.memtotal 16384
env.warning 90
env.critical 95

The real power comes from combining both tools. Here's how I typically integrate them:

# Nagios command definition for Munin alerts
define command {
    command_name    check_munin_threshold
    command_line    /usr/local/bin/check_munin -h $HOSTADDRESS$ -p $ARG1$ -w $ARG2$ -c $ARG3$
}

For your 20-machine environment, consider these performance benchmarks from my implementation:

To address your Nagios setup pain points, try these templating approaches:

# Using Nagios templates (nagios.cfg)
define host {
    name                    linux-server-template
    check_command           check-host-alive
    max_check_attempts      3
    notification_interval   120
    register                0
}

For Munin, auto-discovery plugins can save hours:

# Auto-configure Munin nodes (munin-node-configure)
munin-node-configure --shell --families auto | sh
munin-node-configure --suggest

Here's how I monitor web cluster health across both systems:

# Nagios service group for web servers
define servicegroup {
    servicegroup_name       web-cluster
    alias                   Web Server Cluster
    members                 web01,HTTP,web02,HTTP,web03,HTTP
}

# Corresponding Munin graph aggregation
[webcluster;Aggregated]
web01.download_rate.value \
web02.download_rate.value \
web03.download_rate.value \