Ansible Patterns

Introduction

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- specifies on which hosts in the inventory ansible will talk to

- used on the ff:

    a. ad-hoc commands

    b. plays

- examples patterns in ad-hoc commands:

    ansible webservers -m yum -a "name=httpd state=present"

    ansible -i ~/my_hosts db1:db2 -m ping

- some patterns like "!" and "&" needs to be escaped ("\") in shell

List of Patterns that can be used

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all hosts	all *
hosts w/o a group	ungrouped
specific hosts or set of hosts	one.example.com one.example.com:two.example.com 192.0.2.50 192.0.2.* *.example.com *.com
one or more groups	All hosts under webservers group webservers Colon indicates "or" which means the host may be in one group or the other. Host will still be managed if it is on both groups. webservers:dbservers In version 1.9, you can use "," instead of ":". "," is preferrable on ranges dealing with IPv6. As of version 2.0, ";" is deprecated as a host separator.
excluding a group	All hosts must be in webservers but not in phoenix. Any host that is a member of webservers but also a member of phoenix will not be managed. webservers:!phoenix
intersection	Ampersand means "and". Hosts must be in webservers and must also be in staging. webservers:&staging
combination	All machines in webservers and dbservers must be in staging also to be managed. Machines will not be managed if they are in phoenix. webservers:dbservers:&staging:!phoenix
passing variables	webservers:!{{excluded}}:&{{required}}
mixing wildcards and groups	one*.com:dbservers
selecting by position	In this example group, [webservers] cobweb webbing weber you can refer to hosts by specifying a subscript: webservers[0]       # == cobweb webservers[-1]      # == weber webservers[0:1]     # == webservers[0],webservers[1]                     # == cobweb,webbing webservers[1:]      # == webbing,weber
using regular expressions	~(web|db).*\.example\.com
limiting	This will talk to hosts within datacenter2 group only. This can be used in "ansible" or "ansible-playbook" commands ansible-playbook site.yml --limit datacenter2 ansible all --limit datacenter2 -m ping
getting from a file	You can read list of hosts from a filename with "@" (available on version 1.2 up). This is commonly used to retry a playbook on failed hosts. ansible-playbook site.yml --limit @retry_hosts.txt