Only run Ansible task on box in specific group - ansible

Question

I am trying to create a task that will only run on a box that is in a specific group (called pi).
I am using Ansible version:
ansible 2.3.2.0
config file = /Users/user/Development/raspbian-homeassistant/ansible.cfg
configured module search path = Default w/o overrides
python version = 3.6.3 (default, Dec 3 2017, 10:37:53) [GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.38)]
This is my current code:
- name: Set up zwave USB dongle
when: inventory_hostname in groups['pi']
blockinfile:
path: /var/local/homeassistant/.homeassistant/configuration.yaml
marker: "# {mark} ANSIBLE MANAGED BLOCK #"
insertafter: "# zwave dongle"
content: |2
zwave:
usb_path: /dev/ttyACM0
tags:
- config
- hass
It seems to work correctly when the hostname is in the group but throws an error when not.
This is the error I get when I run it on my vagrant box (in group vagrant):
fatal: [192.168.33.123]: FAILED! => {"failed": true, "msg": "The conditional check 'inventory_hostname in groups['pi']' failed. The error was: error while evaluating conditional (inventory_hostname in groups['pi']): Unable to look up a name or access an attribute in template string ({% if inventory_hostname in groups['pi'] %} True {% else %} False {% endif %}).\nMake sure your variable name does not contain invalid characters like '-': argument of type 'StrictUndefined' is not iterable\n\nThe error appears to have been in '/Users/andy/Development/raspbian-homeassistant/ansible/roles/configure-hass/tasks/main.yml': line 21, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: Set up zwave USB dongle\n ^ here\n"}
Check if a list contains an item in Ansible suggests I have the syntax right but I guess that is for an older version of Ansible?
How do I fix this?

Answer 1

Generally, if you want tasks to apply only to hosts in a particular group, the way you do that is by creating a play that targets that group:
- hosts: pi
tasks:
- name: Set up zwave USB dongle
blockinfile:
path: /var/local/homeassistant/.homeassistant/configuration.yaml
marker: "# {mark} ANSIBLE MANAGED BLOCK #"
insertafter: "# zwave dongle"
content: |2
zwave:
usb_path: /dev/ttyACM0
tags:
- config
- hass
The error you're getting is because groups['pi']is undefined. There are a couple of ways of preventing the error. For example, you can explicitly check thatgroups['pi']` is defined before trying to use it:
- name: set up zwave USB dongle
when: groups['pi'] is defined and inventory_hostname in groups['pi']
Or you can use the default filter to provide a default value:
- name: set up zwave USB dongle
when: inventory_hostname in groups['pi']|default([])