Host File Best Practices

What to Include in Host Files

The key to effective host file usage is selective inclusion of truly critical resources. Host files should not attempt to replace DNS entirely, but rather provide a safety net for essential infrastructure.

Essential Entries for All Servers:

1. DNS Servers (Highest Priority):

   • Without these, you cannot fix DNS when it fails
   • Include both IPv4 and IPv6 addresses
   • List all DNS servers in your infrastructure

   10.1.1.53       dns1.example.com dns1
   10.1.1.54       dns2.example.com dns2
   2001:db8:1::53  dns1.example.com
   2001:db8:1::54  dns2.example.com
   

2. Default Gateway/Router:

   • Essential for network troubleshooting
   • Required for routing configuration access

   10.0.0.1        gateway.example.com gw router
   2001:db8::1     gateway.example.com
   

3. Authentication Infrastructure:

   • LDAP servers, Active Directory domain controllers
   • Critical for user authentication and authorization

   10.3.0.5        ldap.example.com
   10.3.0.6        dc1.example.com ad1
   2001:db8:3::5   ldap.example.com
   

Application-Specific Entries:

4. Database Servers (for application servers):

   10.2.0.10       db-master.example.com
   10.2.0.11       db-replica.example.com
   fd00:db::10     db-master.example.com
   

5. Monitoring and Management Systems:

   10.4.0.20       nagios.example.com monitoring
   10.4.0.21       grafana.example.com metrics
   10.4.0.25       syslog.example.com
   

6. Time Servers (NTP):

   • Critical for accurate logging and certificate validation

   10.5.0.1        ntp1.example.com
   10.5.0.2        ntp2.example.com
   

IT Workstation Additions:

IT administrator workstations should include comprehensive entries for:

• All network equipment management interfaces (switches, routers, firewalls)
• Server management interfaces (iDRAC, iLO, IPMI)
• Virtualization infrastructure (vCenter, ESXi hosts)
• Backup systems
• Security appliances

Host File Best Practices

Organization and Maintenance:

1. Group Entries Logically:

   • Separate sections for different infrastructure types
   • Use clear, descriptive comments
   • Maintain consistent formatting

   # DNS Infrastructure - Critical
   10.1.1.53       dns1.example.com dns1
   10.1.1.54       dns2.example.com dns2
   
   # Database Tier
   10.2.0.10       db-master.example.com db-master
   10.2.0.11       db-replica.example.com db-replica
   

2. Document Changes:

   • Add dates and reasons for modifications
   • Track who made changes and why
   • Consider using configuration management tools (Ansible, Puppet)

3. Version Control:

   • Keep backups of host files
   • Consider storing in Git for change tracking
   • Document the canonical version source

4. Include Both IPv4 and IPv6:

   • Modern networks increasingly use IPv6
   • Maintain both address families for resilience
   • Ensure consistency between IPv4 and IPv6 entries

Distribution and Automation:

5. Automate Deployment:

   • Use configuration management for consistent distribution
   • Avoid manual edits across multiple servers
   • Implement validation before deployment

6. Regular Audits:

   • Verify entries are current and accurate
   • Remove obsolete entries
   • Check for conflicts or duplicates

7. Test Changes:

   • Validate syntax before deployment
   • Verify entries resolve correctly
   • Flush DNS cache after updates

When Host Files Are Not Appropriate

While host files provide critical failsafe capabilities, they have limitations:

Don’t Use Host Files For:

• Dynamic Content: Services with frequently changing IP addresses
• Load Balancing: Host files cannot distribute traffic across multiple servers
• Large-Scale Management: Networks with thousands of hosts should use DNS
• Wildcard Entries: Host files don’t support *.example.com patterns
• Mobile/Roaming Clients: Devices that move between networks need DNS

Host Files vs. DNS:

Host files complement DNS; they don’t replace it. Use DNS for:

• Dynamic service discovery
• Load balancing and failover
• Large numbers of hosts (500+)
• Frequently changing infrastructure
• Geographic distribution and optimization

Use host files for:

• Critical infrastructure failsafe
• Emergency access during DNS outages
• Static, high-priority resources
• Bootstrap operations before DNS is available

Integration with Configuration Management

Modern infrastructure automation makes host file management straightforward:

Ansible Example:

- name: Deploy critical hosts file entries
  blockinfile:
    path: /etc/hosts
    block: |
      # Critical Infrastructure - Managed by Ansible
      10.1.1.53       dns1.example.com dns1
      10.1.1.54       dns2.example.com dns2
      10.0.0.1        gateway.example.com gw      
    marker: "# {mark} ANSIBLE MANAGED INFRASTRUCTURE BLOCK"

Puppet Example:

host { 'dns1.example.com':
  ensure       => present,
  ip           => '10.1.1.53',
  host_aliases => ['dns1'],
}

This approach ensures:

• Consistent host files across infrastructure
• Centralized management
• Version-controlled changes
• Rapid updates when infrastructure changes

Practical Workflow Examples:

Example 1: Infrastructure Server Host File

1. User tags critical infrastructure in ResorsIT (DNS servers, gateways, databases)
2. Select “Generate Host File” → “Infrastructure Servers Template”
3. ResorsIT exports all tagged hosts with current IP addresses and aliases
4. Output includes both IPv4 and IPv6 entries automatically
5. Deploy via Ansible/Puppet to all production servers
6. When IP changes, regenerate and redeploy in minutes

Example 2: IT Workstation Host File

1. Select subnets containing management interfaces (IPMI, iDRAC, iLO)
2. Add all DNS servers from the DNS infrastructure
3. Include network equipment management IPs
4. ResorsIT generates comprehensive host file with 200+ entries
5. Deploy to all IT administrator workstations
6. Update quarterly or when major infrastructure changes occur

Example 3: Emergency Access Host File

1. Tag “emergency access only” hosts: DNS servers, critical gateways, authentication
2. Generate minimal host file (20-30 entries)
3. Deploy to ALL servers as absolute minimum failsafe
4. These entries ensure basic infrastructure access during total DNS failure

Infrastructure Visibility for Smart Selection:

• Visual subnet management shows IP allocations and utilization
• Cross-reference DNS records with subnet assignments to find discrepancies
• Identify critical infrastructure through subnet categorization (management, production, infrastructure)
• Tag-based selection: Mark hosts as critical, infrastructure, monitoring, etc.
• Dependency mapping: Identify which services depend on which infrastructure

Change Tracking and Audit Trail:

• Audit logs (SaaS) or Git-backed history (Platform) of all DNS and IP changes
• Audit trail shows who changed what infrastructure and when
• Rollback capabilities: Revert to previous configurations when needed (Platform)
• Host file versioning: Track which host file version was deployed when
• Change notifications: Alert when critical infrastructure IPs change

Validation and Consistency:

• Detect conflicts between DNS records and subnet allocations
• Validate syntax before host file generation (no typos or malformed entries)
• Ensure consistency between IPv4 and IPv6 entries
• Check for duplicates: Prevent same hostname with different IPs
• Alias validation: Ensure aliases are unique and don’t conflict

Integration with Configuration Management:

Ansible Integration Example:

- name: Generate host file from ResorsIT
  uri:
    url: https://resorsit.example.com/api/hostfile/infrastructure
    method: GET
    return_content: yes
  register: hostfile_content

- name: Deploy to servers
  blockinfile:
    path: /etc/hosts
    block: "{{ hostfile_content.content }}"
    marker: "# {mark} RESORSIT MANAGED INFRASTRUCTURE"

API-Driven Updates:

• ResorsIT provides REST API for host file generation
• Automated daily/weekly regeneration via cron or scheduled jobs
• Conditional updates: only deploy if infrastructure changed
• Notification when host file needs updating

Benefits Over Manual Management:

• Elimination of human error: No typos, formatting mistakes, or forgotten entries
• Always current: Generate from live data, not outdated spreadsheets
• Reduced maintenance time: Minutes instead of hours to update host files
• Consistent across fleet: All servers get identical infrastructure entries
• Documented decisions: Tags and categories explain why each host is included
• Easy auditing: Clear record of what’s in host files and why

Typical ResorsIT Host File Management Workflow:

1. Initial Setup: Tag critical infrastructure in ResorsIT (one-time effort)
2. Template Creation: Define role-based templates (servers, workstations, network gear)
3. Automated Generation: Schedule or trigger host file exports
4. Deployment: Use configuration management to distribute
5. Maintenance: When infrastructure changes, regenerate and redeploy
6. Audit: Quarterly review of which hosts are tagged as critical

By maintaining DNS and IP data as a single source of truth, ResorsIT eliminates the tedious, error-prone work of manually maintaining host files across your infrastructure. Users retain full control over which hosts are included (based on criticality assessment), while ResorsIT handles the mechanics of generation, formatting, validation, and keeping everything synchronized with your actual infrastructure.