linux-sysadmin-journey/projects/01-homelab-setup/lessons-learned.md

Lessons Learned & Challenges

Network Configuration

Lessons Learned

1. Network Adapters

   • NAT adapter is essential for internet access
   • Host-only adapter enables direct communication with host machine
   • Each adapter serves a specific purpose in the VM setup

2. IP Addressing

   • NAT adapter typically gets 10.0.2.15/24 in VirtualBox
   • Host-only adapter uses 169.254.x.x range (link-local addressing)
   • Understanding different IP ranges helps with troubleshooting

Challenges Faced

1. Host-only Network Issues
   • Initial "state DOWN" on enp0s8 interface
   • Required proper netplan configuration to resolve
   • Solution: Explicitly configure network interfaces in netplan

Security Setup

Lessons Learned

1. User Management

   • Creating admin user first ensures backup access
   • Group membership (especially sudo) is crucial for administration
   • Verify permissions immediately after changes

2. SSH Configuration

   • Always backup sshd_config before modifications
   • Test SSH access before disabling password authentication
   • Key order of operations:
     1. Set up SSH keys
     2. Test key-based login
     3. Only then disable password authentication

3. Firewall Configuration

   • Always allow SSH before enabling UFW
   • Default deny incoming, allow outgoing is a secure baseline
   • Document all allowed ports/services for future reference

Challenges Faced

1. SSH Key Setup

   • Proper file permissions are critical (700 for .ssh, 600 for authorized_keys)
   • Windows line endings can cause issues with key files
   • Solution: Use proper chmod commands and verify permissions

2. UFW Configuration

   • Risk of losing SSH access when enabling firewall
   • Solution: Always add SSH rule before enabling UFW
   • Remember to allow both IPv4 and IPv6 traffic if needed

Best Practices Discovered

1. Documentation

   • Document commands as you execute them
   • Keep track of configuration changes
   • Note IP addresses and network settings

2. Testing

   • Test each change immediately
   • Have a backup plan (like VirtualBox GUI access)
   • Verify services after system changes

3. Security

   • Follow principle of least privilege
   • Use key-based authentication over passwords
   • Keep system updated and maintain secure configurations

Quick Reference Commands

# Network Verification
ip addr show                # Check network interfaces
ping -c 4 8.8.8.8          # Test internet connectivity
ss -tulpn                  # List listening ports

# SSH Security
ssh-keygen -t rsa -b 4096  # Generate SSH key
ssh-copy-id user@host      # Copy SSH key to server
chmod 700 ~/.ssh           # Set correct permissions

# UFW Management
sudo ufw status numbered   # List rules with numbers
sudo ufw delete NUMBER     # Remove specific rule
sudo ufw reload           # Apply changes without disable/enable

Future Considerations

1. Monitoring

   • Consider setting up basic system monitoring
   • Implement log monitoring
   • Regular security audits

2. Maintenance

   • Regular backup strategy
   • Update management plan
   • Documentation maintenance