group_vars & host_vars

Lesson 8 gave you groups. This lesson gives them configuration, through two directories next to your inventory file: group_vars and host_vars . The entire trick is in the filenames:

inventory/
├── hosts.yml           # your lesson-8 inventory: web, db, all the groups
├── group_vars/
│   ├── all.yml         # every host in the inventory — keep it minimal
│   └── web.yml         # every host in the web group
└── host_vars/
    └── web01.yml       # exactly one machine: web01

No import line, no path setting, no reference from the inventory. Ansible auto-loads each file by matching its name against your group and host names. group_vars/web.yml applies to every host in web; host_vars/web01.yml to the single host web01. group_vars/all.yml applies to everything, because every host belongs to the built-in all group. A vars file is just YAML keys and values:

# loaded automatically for every host in the web group
app_env: staging
http_port: 8080
motd_message: 'managed by ansible - do not hand-edit'

Where environment config lives

The rule is blunt: environment config lives here. Ports, service endpoints, tuning values — anything that varies between staging and production belongs in group_vars. Not hardcoded into a playbook, not scattered across the inventory file. When roles arrive in Unit 6, you’ll see the full division of labour: user-tunable defaults in the role, environment values in group_vars.

Two habits separate tidy repos from haunted ones:

• Keep group_vars/all.yml minimal. A value there touches every host in the inventory, so it must be genuinely universal. Environment-specific values belong in the environment’s own inventory directory — more on that below.
• Use host_vars/ sparingly, for values true of one machine only. If you’re writing the same key into three host files, those hosts want to be a group.

Your inventory now says who your hosts are and what is true about them, all loaded by naming convention. Real repos go one step further: a separate inventory directory per environment (inventories/production/, inventories/staging/), each with its own group_vars and host_vars. So staging values can never bleed into prod. The structure — plus the patterns that pick which hosts a run touches — is lesson 10.