Ansible Inventory & Variable Management

Advancedv1.0.0

Design Ansible inventories for multi-environment infrastructure — static and dynamic inventories, group variables, host variables, and variable precedence for complex deployments.

Content

Overview

Ansible inventory defines your infrastructure — which hosts exist, how they are grouped, and what variables apply to each group and host. Proper inventory design is the foundation of scalable Ansible automation.

Why This Matters

-Environment separation — different configs for dev/staging/production
-Group-based automation — target webservers, databases, or regions
-Variable inheritance — group vars override defaults, host vars override groups
-Dynamic scaling — auto-discover cloud instances

Directory-Based Inventory

code

inventory/
├── production/
│   ├── hosts.yml           # Host definitions
│   ├── group_vars/
│   │   ├── all/
│   │   │   ├── vars.yml    # Shared variables
│   │   │   └── vault.yml   # Encrypted secrets
│   │   ├── webservers.yml  # Web server config
│   │   └── databases.yml   # Database config
│   └── host_vars/
│       └── db-primary.yml  # Host-specific overrides
├── staging/
│   ├── hosts.yml
│   └── group_vars/
│       └── all/
│           └── vars.yml
└── development/
    └── hosts.yml

Static Inventory (YAML)

yaml

# inventory/production/hosts.yml
all:
  children:
    webservers:
      hosts:
        web-01.prod:
          ansible_host: 10.0.1.10
        web-02.prod:
          ansible_host: 10.0.1.11
    databases:
      hosts:
        db-primary.prod:
          ansible_host: 10.0.2.10
          db_role: primary
        db-replica.prod:
          ansible_host: 10.0.2.11
          db_role: replica
    loadbalancers:
      hosts:
        lb-01.prod:
          ansible_host: 10.0.0.10

Group Variables

yaml

# inventory/production/group_vars/all/vars.yml
---
environment: production
domain: myapp.com
ntp_servers:
  - 0.pool.ntp.org
  - 1.pool.ntp.org
monitoring_enabled: true
log_level: warn

# inventory/production/group_vars/webservers.yml
---
nginx_worker_processes: 4
nginx_worker_connections: 4096
app_port: 8080
app_replicas: 3

# inventory/production/group_vars/databases.yml
---
postgresql_version: 16
postgresql_max_connections: 200
postgresql_shared_buffers: "4GB"
backup_enabled: true
backup_schedule: "0 2 * * *"

Dynamic Inventory (AWS)

yaml

# aws_ec2.yml
plugin: amazon.aws.aws_ec2
regions:
  - us-east-1
keyed_groups:
  - key: tags.Environment
    prefix: env
  - key: tags.Role
    prefix: role
filters:
  instance-state-name: running
compose:
  ansible_host: private_ip_address

bash

# Use dynamic inventory
ansible-playbook -i aws_ec2.yml site.yml

Variable Precedence (Low to High)

code

1. Role defaults (defaults/main.yml)
2. Inventory group_vars/all
3. Inventory group_vars/<group>
4. Inventory host_vars/<host>
5. Play vars
6. Role vars (vars/main.yml)
7. Task vars
8. Extra vars (-e / --extra-vars)  ← HIGHEST

Best Practices

-One inventory directory per environment (production/, staging/, development/)
-Use group_vars/all/ for shared settings, group-specific files for overrides
-Keep host_vars minimal — most config should be at group level
-Use dynamic inventory for cloud environments (auto-discover instances)
-Separate vars.yml (plain) from vault.yml (encrypted) in each group

Common Mistakes

-Single flat inventory file for all environments
-Host-specific variables that should be group variables
-Not understanding variable precedence (unexpected overrides)
-Hardcoding IPs instead of using DNS or dynamic inventory

FAQ

Discussion

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Directory-Based Inventory

code

inventory/
├── production/
│   ├── hosts.yml           # Host definitions
│   ├── group_vars/
│   │   ├── all/
│   │   │   ├── vars.yml    # Shared variables
│   │   │   └── vault.yml   # Encrypted secrets
│   │   ├── webservers.yml  # Web server config
│   │   └── databases.yml   # Database config
│   └── host_vars/
│       └── db-primary.yml  # Host-specific overrides
├── staging/
│   ├── hosts.yml
│   └── group_vars/
│       └── all/
│           └── vars.yml
└── development/
    └── hosts.yml

Static Inventory (YAML)

yaml

# inventory/production/hosts.yml
all:
  children:
    webservers:
      hosts:
        web-01.prod:
          ansible_host: 10.0.1.10
        web-02.prod:
          ansible_host: 10.0.1.11
    databases:
      hosts:
        db-primary.prod:
          ansible_host: 10.0.2.10
          db_role: primary
        db-replica.prod:
          ansible_host: 10.0.2.11
          db_role: replica
    loadbalancers:
      hosts:
        lb-01.prod:
          ansible_host: 10.0.0.10

Group Variables

yaml

# inventory/production/group_vars/all/vars.yml
---
environment: production
domain: myapp.com
ntp_servers:
  - 0.pool.ntp.org
  - 1.pool.ntp.org
monitoring_enabled: true
log_level: warn

# inventory/production/group_vars/webservers.yml
---
nginx_worker_processes: 4
nginx_worker_connections: 4096
app_port: 8080
app_replicas: 3

# inventory/production/group_vars/databases.yml
---
postgresql_version: 16
postgresql_max_connections: 200
postgresql_shared_buffers: "4GB"
backup_enabled: true
backup_schedule: "0 2 * * *"

Dynamic Inventory (AWS)

yaml

# aws_ec2.yml
plugin: amazon.aws.aws_ec2
regions:
  - us-east-1
keyed_groups:
  - key: tags.Environment
    prefix: env
  - key: tags.Role
    prefix: role
filters:
  instance-state-name: running
compose:
  ansible_host: private_ip_address

bash

# Use dynamic inventory
ansible-playbook -i aws_ec2.yml site.yml

1. Role defaults (defaults/main.yml) 2. Inventory group_vars/all 3. Inventory group_vars/<group> 4. Inventory host_vars/<host> 5. Play vars 6. Role vars (vars/main.yml) 7. Task vars 8. Extra vars (-e / --extra-vars) ← HIGHEST

Best Practices

-One inventory directory per environment (production/, staging/, development/)

-Use group_vars/all/ for shared settings, group-specific files for overrides

-Keep host_vars minimal — most config should be at group level

-Use dynamic inventory for cloud environments (auto-discover instances)

-Separate vars.yml (plain) from vault.yml (encrypted) in each group