When working with Puppet in NAT environments, a common frustration occurs when the reverse DNS resolution doesn't match the desired hostname configuration. The client machine reports its FQDN as office.mydomain.com due to network topology, but we need it to identify as ns2.mydomain.com for proper Puppet classification.

Puppet uses several methods to determine a node's identity:

• SSL certificate common name (certname)
• Reverse DNS resolution
• System hostname configuration
• Explicit configuration in puppet.conf

# Typical identification flow:
1. Client initiates connection with current hostname
2. Server checks certname first if configured
3. Falls back to FQDN from system/DNS
4. Matches against node definitions in manifests

The key is to properly configure the certname setting while ensuring fact collection works correctly. Here's the optimal puppet.conf configuration:

[main]
certname = ns2.mydomain.com
node_name = cert
dns_alt_names = ns2,ns2.mydomain.com
use_cached_catalog = false

[agent]
report = true
pluginsync = true

The missing facts ($fqdn, $operatingsystem) suggest deeper configuration problems. Implement these fixes:

# On the client machine:
# Ensure proper hostname configuration
hostnamectl set-hostname ns2.mydomain.com

# In /etc/hosts
127.0.0.1   ns2.mydomain.com ns2 localhost

# Then clean and regenerate certs
sudo rm -rf /etc/puppetlabs/puppet/ssl
sudo puppet agent -t --noop

For complex environments, consider implementing an ENC to override node classification:

#!/bin/bash
# Example ENC script for hostname override
CERTNAME=$(puppet config print certname)

case $CERTNAME in
  "ns2.mydomain.com")
    echo "classes:"
    echo "  - role::dns::secondary"
    echo "environment: production"
    ;;
  *)
    echo "classes:"
    echo "  - role::generic"
    echo "environment: development"
    ;;
esac

When working behind NAT, ensure proper network configuration:

• Enable report=true in puppet.conf
• Check firewall rules for Puppet port (8140)
• Verify time synchronization (NTP)
• Ensure consistent DNS resolution between client and server

For complete verification, run these diagnostic commands:

puppet config print all | grep -E 'certname|node_name'
facter | grep -E 'fqdn|hostname|ipaddress'
openssl x509 -in /etc/puppetlabs/puppet/ssl/certs/$(hostname).pem -text | grep DNS

When working with Puppet in NAT environments, many administrators encounter node naming conflicts where reverse DNS resolution doesn't match desired Puppet configurations. The fundamental issue manifests when a server's reverse DNS (like office.mydomain.com) differs from its intended Puppet node name (ns2.mydomain.com).

By default, Puppet determines the node name through these steps:

1. Checks the node_name fact (usually fqdn)
2. Falls back to reverse DNS resolution
3. Uses the certname setting as final fallback

The current configuration attempts to force the node name using these puppet.conf settings:

[main]
certname=ns2.mydomain.com
node_name=cert

While this should work in theory, the syslog output shows the master still processes the node as office.mydomain.com:

Sep 16 22:59:12 support puppetmasterd[2800]: Compiled catalog for office.mydomain.com
Sep 16 22:59:12 support puppetmasterd[2800]: Caching catalog for ns2.mydomain.com

To reliably override reverse DNS naming in NAT environments:

1. Client-Side Configuration

[main]
certname = ns2.mydomain.com
node_name = cert
use_srv_records = false

[agent]
node_name_value = ns2.mydomain.com

2. Server-Side Precedence Rules

In puppet.conf on the master:

[master]
node_terminus = plain
strict_hostname_checking = false

3. Alternative DNS Configuration

For environments where you control DNS:

# /etc/hosts on the Puppet master
192.168.1.100  ns2.mydomain.com ns2

The reported missing facts ($fqdn, $operatingsystem) typically indicate:

• Facter not running properly
• Network connectivity issues preventing fact collection
• Time synchronization problems

Debug with:

puppet facts find ns2.mydomain.com --render-as json
facter -p

For complex environments, consider an ENC (External Node Classifier) that overrides naming:

#!/bin/bash
# /etc/puppetlabs/code/environments/production/scripts/enc.sh

CERTNAME=$1
REALNAME=$(echo $CERTNAME | sed 's/office./ns2./g')

cat <

[master]
node_terminus = exec
external_nodes = /etc/puppetlabs/scripts/enc.sh