Ansible: Combine group and host vars

In Ansible the configuration parameters are usually separated into two categories: host and group vars. As their names say these are variables that are either applied to a specific host or a group of hosts. And here is already an edge case. What if we want to configure a variable for group, but then also give the possibility to modify for a specific host. Read on to see my solution.

This use case occurs usually for list vars. In this example we have a list of packages that need to be installed for a host. We have default group setting the packages var, but then there is also a host specific variable.

This is the group var:

inventory/group_vars/all.yml

packages:
  - name: git
  - name: dnsutils
  - name: zsh

For the host var prefix the var with host_. This helps to make a distinction and of course not overwriting the group var.

inventory/host_vars/server1.yml

host_packages:
  - name: cifs-utils

If the variable is list of dictionaries, it is easy to merge the two variables:

roles/packages/tasks/main.yml

- name: Combine group and host vars
  set_fact:
    packages: "{{ packages + host_packages }}"
  when: host_packages is defined

I recommend to define any list as a list of dictionaries.