Group and host vars

Ansible is a variable driven tool, just as Terraform for example. Variables are used to store information, and to make decisions.

Group vars and host vars are a way to store variables for a group of hosts, or a single host.

Think of this scructure:

Let’s define some variable applicable to all hosts:

group_vars/all/backup.yml:

backup_interval: 3600

Now let’s set a path to backup for the webservers:

group_vars/webservers/backup.yml

backup_paths:
  - /var/www/html

And backup something else for the databaseservers:

group_vars/databaseservers/backup.yml

backup_paths:
  - /var/lib/mysql

As you can see, you can set a value for a variable based on the group the host is in.

The same works for host vars, but then for a single host. The group_vars are mostly more applicable than host_vars, but you can use both.

More specific variables will override the more general ones. The different levels and priority is described in the Ansible documentation.

Assignment

Note: This assignment requires the previous assignment on inventory to be completed.

1. Create a group_vars directory.
2. Create a group_vars/all/ntp.yml file.
3. Set the ntp_server variable to 0.pool.ntp.org for all hosts.
4. Create a group_vars/switzerland/ntp.yml file.
5. Set the ntp_server variable to 0.ch.pool.ntp.org for all hosts in the switzerland group.
6. Set the ntp_server variable to 0.nl.pool.ntp.org for all hosts in the netherlands group.

Verify

Run ansible netherlands -m debug -a "var=ntp_server". You should see this output:

node-1 | SUCCESS => {
    "ntp_server": "0.nl.pool.ntp.org"
}
node-3 | SUCCESS => {
    "ntp_server": "0.nl.pool.ntp.org"
}

Run ansible switzerland -m debug -a "var=ntp_server". You should see this output:

 node-2 | SUCCESS => {
    "ntp_server": "0.ch.pool.ntp.org"
}
node-4 | SUCCESS => {
    "ntp_server": "0.ch.pool.ntp.org"
}

Solution

The solution can be found in the solution directory.