AnsibleByExample

Ansible Inventory Patterns: Target Groups, Hosts & Access groups Variable

Advanced
2024-01-014By Luca Berton

Lesson 1 of 15 in Foundations

Ansible Foundations to Production — full curriculum
  1. 1. Introduction to Ansible and Automation
  2. 2. Installing and Configuring Ansible
  3. 3. Running Ad-Hoc Commands
  4. 4. Writing Your First Playbook
  5. 5. Understanding and Using Modules
  6. 6. Variables and Facts
  7. 7. Conditionals and Loops
  8. 8. Handlers and Idempotency
  9. 9. Structuring Projects with Roles
  10. 10. Inventory Management
  11. 11. Using Ansible Vault for Secrets
  12. 12. Debugging and Troubleshooting
  13. 13. Real-World Automation Examples
  14. 14. Final Project: Deploy a Web Server
  15. 15. Bonus - What's Next with Ansible?
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Ansible Inventory Patterns — Target Hosts and Groups

Introduction

Inventory patterns control which hosts Ansible targets. Instead of running against all hosts, you can target specific groups, use wildcards, combine groups with AND/OR/NOT logic, and use regex — all from the command line or in playbooks.

Basic Patterns

# All hosts
ansible all -m ping

# Specific group
ansible webservers -m ping

# Specific host
ansible db01 -m ping

# Multiple groups
ansible 'webservers:databases' -m ping

# Multiple hosts
ansible 'web01:web02:db01' -m ping

Wildcard Patterns

# All hosts starting with "web"
ansible 'web*' -m ping

# All .example.com hosts
ansible '*.example.com' -m ping

# Single character wildcard
ansible 'web0?' -m ping  # web01, web02, ... web09

Group Operations

Union (OR) — hosts in either group

ansible 'webservers:databases' -m ping

Intersection (AND) — hosts in BOTH groups

ansible 'webservers:&production' -m ping
# Only hosts that are in webservers AND production

Exclusion (NOT) — hosts NOT in a group

ansible 'webservers:!staging' -m ping
# Webservers that are NOT in staging

Complex Patterns

# Production webservers, excluding hosts being patched
ansible 'webservers:&production:!patching' -m ping

# All hosts in either web or db, but only in production
ansible 'webservers:databases:&production' -m ping

Regex Patterns

# Regex (prefix with ~)
ansible '~web[0-9]+\.example\.com' -m ping

# Match numbered hosts
ansible '~^(web|db)[0-9]{2}$' -m ping

Numeric Ranges

# inventory.yml — range shorthand
all:
  children:
    webservers:
      hosts:
        web[01:50]:           # web01 through web50
        web[a:f]:             # weba through webf
    databases:
      hosts:
        db-[01:03]:           # db-01, db-02, db-03
    caches:
      hosts:
        192.168.1.[10:20]:    # IP range

Playbook Targeting

# Target specific groups in playbooks
---
- name: Configure all web servers
  hosts: webservers
  tasks: [...]

- name: Configure production databases only
  hosts: databases:&production
  tasks: [...]

- name: All servers except staging
  hosts: all:!staging
  tasks: [...]

# Dynamic host targeting
- name: Target from variable
  hosts: "{{ target_hosts | default('all') }}"
  tasks: [...]

# Override at runtime
ansible-playbook site.yml -e "target_hosts=web01"

--limit Flag

Restrict targets at runtime without editing playbooks:

# Limit to one host
ansible-playbook site.yml --limit web01

# Limit to multiple hosts
ansible-playbook site.yml --limit 'web01,web02'

# Limit with pattern
ansible-playbook site.yml --limit 'web*'

# Limit to group intersection
ansible-playbook site.yml --limit 'webservers:&production'

# Exclude hosts
ansible-playbook site.yml --limit 'all:!db01'

# Retry failed hosts from last run
ansible-playbook site.yml --limit @site.retry

Inventory Listing

# Show all hosts in inventory
ansible-inventory --list

# Show hosts matching a pattern
ansible-inventory --host web01

# Graph view
ansible-inventory --graph

# Graph of specific group
ansible-inventory --graph webservers

Output:

@all:
  |--@webservers:
  |  |--web01
  |  |--web02
  |--@databases:
  |  |--db01
  |--@ungrouped:
  |  |--monitoring01

Special Groups

GroupContains
allEvery host in inventory
ungroupedHosts not in any group (except all)
localhostThe control machine
# Target localhost explicitly
- hosts: localhost
  connection: local
  tasks:
    - name: Run locally
      ansible.builtin.debug:
        msg: "Running on controller"

Nested Groups

# inventory.yml
all:
  children:
    production:
      children:
        prod_web:
          hosts:
            web01:
            web02:
        prod_db:
          hosts:
            db01:
    staging:
      children:
        stag_web:
          hosts:
            stag-web01:
        stag_db:
          hosts:
            stag-db01:

# Target all production (web + db)
ansible production -m ping

# Target only production web servers
ansible prod_web -m ping

Troubleshooting

IssueSolution
"No hosts matched"Check pattern syntax and inventory: ansible-inventory --list
Wrong hosts selectedUse --list-hosts to preview: ansible-playbook site.yml --list-hosts
Host in wrong groupCheck inventory structure: ansible-inventory --graph
Pattern not workingQuote patterns with special chars: ansible 'web*:&prod' -m ping

Best Practices

  1. Use semantic group names — webservers, databases, not group1
  2. Nest groups for environments — production > prod_web, staging > stag_web
  3. Use --limit for one-offs — don't edit inventory for temporary restrictions
  4. Test with --list-hosts — preview targeting before running
  5. Avoid all in production — be explicit about which hosts you target

Conclusion

Inventory patterns give you surgical precision in host targeting. Master union (:), intersection (&), and exclusion (!) operators, and you can target any combination of hosts without modifying your inventory or playbooks.

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