[host_group]
host-1 ansible_ssh_host=192.168.0.21 node_name=foo
host-2 ansible_ssh_host=192.168.0.22 node_name=bar
[host_group:vars]
custom_var=asdasdasd
You can access host group vars using:
{{ hostvars['host_group'].custom_var }}
If you need a specific value from specific host, you can use:
{{ hostvars[groups['host_group'][0]].node_name }}