Many sysadmins face the frustrating issue where their carefully configured iptables rules disappear after a reboot. This is particularly common on cloud instances like AWS EC2 where network interfaces behave differently than traditional servers.

The traditional approach of placing scripts in /etc/network/if-pre-up.d/ often fails because:

• Cloud-init may initialize networking before these scripts run
• Network interfaces come up in unpredictable order
• Some AMIs have custom network initialization sequences

Here are several proven methods to persist iptables rules:

Method 1: Using rc.local

Edit /etc/rc.local:

#!/bin/sh -e
#
# rc.local

iptables-restore < /etc/iptables.rules

exit 0

Make it executable:

chmod +x /etc/rc.local

Method 2: Systemd Service

Create /etc/systemd/system/iptables-restore.service:

[Unit]
Description=Restore iptables rules
After=network.target

[Service]
Type=oneshot
ExecStart=/sbin/iptables-restore /etc/iptables.rules

[Install]
WantedBy=multi-user.target

Then enable it:

systemctl enable iptables-restore.service

Method 3: Network Manager Dispatcher

For systems using NetworkManager:

cat > /etc/NetworkManager/dispatcher.d/99-restore-iptables <<'EOF'
#!/bin/bash

if [ "$1" = "up" ]; then
    /sbin/iptables-restore < /etc/iptables.rules
fi
EOF

chmod +x /etc/NetworkManager/dispatcher.d/99-restore-iptables

When working with persistent rules:

1. Always test rules before making them persistent
2. Use iptables-save > /etc/iptables.rules to create a clean rules file
3. Consider using iptables-persistent package if available
4. Document your rules with comments in the rules file

If your rules still aren't loading:

• Check system logs: journalctl -xe
• Verify network interface names match your configuration
• Test rules manually before automating
• Consider adding a delay before rule restoration

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When working with Amazon EC2 VPC NAT instances running Debian-based AMIs (like ami-1de2d969), administrators often struggle with persisting iptables rules across reboots. The standard Debian approach of using /etc/network/if-pre-up.d/ scripts frequently fails in these cloud environments due to differences in network initialization.

The Amazon EC2 environment has several unique characteristics that affect iptables persistence:

• Network interfaces are managed by cloud-init
• Traditional network initialization scripts might execute too early
• The NAT instance role requires specific rule ordering

After extensive testing on production VPC NAT instances, here are the most reliable approaches:

Method 1: rc.local Approach

While not elegant, this method proves consistently reliable:

#!/bin/bash
iptables-restore < /etc/firewall.conf
exit 0

Save this to /etc/rc.local and ensure the file is executable.

Method 2: Systemd Service Unit

For modern Debian systems using systemd:

[Unit]
Description=Restore iptables rules
After=network.target

[Service]
Type=oneshot
ExecStart=/sbin/iptables-restore /etc/firewall.conf

[Install]
WantedBy=multi-user.target

Save as /etc/systemd/system/iptables-restore.service and enable with:

systemctl enable iptables-restore.service

For production environments, consider this enhanced approach:

#!/bin/bash
# Wait for network interfaces to stabilize
sleep 5

# Flush existing rules
iptables -F
iptables -t nat -F

# Restore persistent rules
iptables-restore < /etc/firewall.conf

# Additional EC2-specific rules
INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
logger "iptables rules restored on instance $INSTANCE_ID"

• Verify rule loading with iptables -L -n -v
• Check system logs for errors
• Test reboots using AWS Systems Manager rather than terminating instances
• Consider using AWS Network Firewall for critical rules

When working with iptables on EC2:

1. Always maintain a backup SSH session when modifying rules
2. Use AWS Session Manager as a fallback access method
3. Document rule changes in version control
4. Consider Terraform or CloudFormation for infrastructure-as-code management