Ansible: host patterns

Definition

Host patterns allow you to specify exactly which nodes require tasks to be performed

Patterns with example:

all or * — all hosts
stage:dev — union/logical OR
stage:&dev — intersection/logical AND
stage:!dev — exclusion
*.example — wildcard
dev[5:10] — host range (counting starts from zero)
~web\d+\.example — regular expressions

Instead of the : separator, you can use , which is preferable when working with IPv6 networks or ranges

The processing order is as follows:

: and ,
&
!

You can use combinations of patterns:

hosts: dev:staging:&database:!queque (all hosts from the dev and staging groups if they are also in the database group, but excluding hosts from the queque group)

You can also use variables to pass groups via -e, --extra-vars, for example: hosts: webservers:!{{ excluded }}:&{{ required }}

You can use it in playbooks and ad-hoc commands, but when using a playbook file, you need to use the -l, --limit flag:

Examples for ansible-playbook and ansible binaries (don’t forget to escape patterns with special bash characters with quotes)

ansible-playbook -l hosts main.yml
ansible-playbook -l 'staging:&database' main.yml
ansible-playbook -l 'staging,&database' main.yml

ansible all:localhost -m setup
ansible all,localhost -m setup
ansible 'staging:&database' -m reboot
ansible 'staging,&database' -m reboot

Playbook example:

- name: Play this on all hosts except db group
  hosts: all:!db
  tasks:
    - name: Change hostname
      ansible.builtin.file:
        use: systemd
        name: "{{ inventory_hostname }}"

- name: Play this on all host that are also in a backup group but not in a web one
  hosts: all:&backup:!web
  tasks:
    - name: Add host record to /etc/hosts
      ansible.builtin.lineinfile:
        path: /etc/hosts
        line: "{{ ansible_host }} {{ inventory_hostname }}"
        state: present
        insertbefore: BOF

Definition#

Definition