Ansible Inventory Design Prompt

You are a senior automation engineer who has organized Ansible inventories for fleets of thousands — multi-env, multi-region, dynamic sources.

I will provide:
- The inventory size + structure
- Current approach (single file, multi-file, dynamic)
- Symptom (wrong hosts targeted, vars not applying, slow gather)

Your job:

1. **Static vs dynamic**:
   - **Static** — INI / YAML; explicit lists
   - **Dynamic** — script / plugin; cloud-derived
   - Most production: hybrid
2. **For static structure**:
   - One file per env: `inventories/production`, `inventories/staging`
   - `hosts.yml` with grouped hosts
   - `group_vars/` and `host_vars/` directories
3. **For dynamic plugins**:
   - `amazon.aws.aws_ec2` for EC2
   - `google.cloud.gcp_compute` for GCP
   - `azure.azcollection.azure_rm` for Azure
   - YAML config in inventory file
4. **For group hierarchy**:
   - Parent groups + child groups
   - `children:` key
   - Vars inherit child → parent
5. **For host_vars / group_vars**:
   - One file per host or group
   - YAML
   - Loaded automatically per inventory
6. **For multi-env**:
   - Separate inventory dirs per env
   - Same playbook
   - `-i inventories/production`
7. **For special groups**:
   - `all` — everything
   - `ungrouped` — no group
   - Group names are case-sensitive
8. **For combining inventories**:
   - Multiple `-i` flags
   - Plugins compose

Mark DESTRUCTIVE: targeting wrong inventory in production, broad `all` matches across envs, dynamic inventory with API auth failures.

---

Inventory size + structure: [DESCRIBE]
Current approach: [DESCRIBE]
Symptom: [DESCRIBE]

Why this prompt works

Inventory is the foundation. This prompt walks design.

How to use it

1. Pick static vs dynamic per env.
2. Group thoughtfully for vars.
3. Multi-env via separate dirs.
4. Test with --list-hosts.

Useful commands

# Show inventory
ansible-inventory -i inventories/production --list
ansible-inventory -i inventories/production --graph

# Test which hosts a pattern matches
ansible -i inventories/production webservers --list-hosts
ansible -i inventories/production all --list-hosts

# Dynamic inventory test
ansible-inventory -i aws_ec2.yml --list

# Validate
ansible-inventory -i inventories/production --syntax-check

Patterns

Static multi-file structure

inventories/
├── production/
│   ├── hosts.yml
│   ├── group_vars/
│   │   ├── all.yml
│   │   ├── webservers.yml
│   │   └── databases.yml
│   └── host_vars/
│       └── db-master-01.yml
├── staging/
│   ├── hosts.yml
│   └── group_vars/
└── dev/
    └── hosts.yml

# inventories/production/hosts.yml
all:
  children:
    webservers:
      hosts:
        web-01.example.com:
        web-02.example.com:
        web-03.example.com:
      vars:
        nginx_workers: 8

    databases:
      children:
        db_primary:
          hosts:
            db-master-01.example.com:
        db_replicas:
          hosts:
            db-replica-01.example.com:
            db-replica-02.example.com:

    production:
      children:
        webservers:
        databases:
      vars:
        env: production

Dynamic inventory (AWS)

# inventories/aws_ec2.yml
plugin: amazon.aws.aws_ec2
regions: [us-east-1, us-west-2]
filters:
  tag:Environment: production
  instance-state-name: running
keyed_groups:
- key: tags.Service
  prefix: service
- key: tags.Tier
  prefix: tier
hostnames:
- private-dns-name
compose:
  ansible_host: private_ip_address

Hybrid (static + dynamic combined)

ansible-playbook -i inventories/production -i aws_ec2.yml playbook.yml

Common findings this catches

• Playbook hits wrong hosts → check --list-hosts first.
• Vars not applying → wrong group_vars file name.
• Dynamic inventory empty → API auth or filter.
• Stale cache → --flush-cache.
• Group hierarchy unexpected → use --graph.
• all matches everything in combined inventories.
• Hostname format wrong in dynamic plugin → use compose.

When to escalate

• Cross-team inventory ownership — coordinate.
• Multi-region / multi-cloud — strategic.
• Migration to dynamic — staged.