Group-based Environments

Problem

When managing Ansible projects for different environments such as development, test, staging, and production, it’s important to have a structured approach to organize inventory and variables.

Context

Ansible allows you to define groups in inventory, which can be used to organize hosts with similar roles or attributes. Group variables can also be used to define environment-specific variables that are applied to hosts in those groups.

Solution

Follow these guidelines to implement a group-based environments strategy in your inventory project:

1. Organize your inventory file within the inventory project and add an Ansible group for each environment (e.g., development, test, staging, production) which we can refer to as environment groups.
2. Assign hosts to appropriate environment groups depending on the environment they are part of, e.g., development hosts to development group, production hosts to production group.
3. Create separate files for group variables for each environment group, e.g., group_vars/development.yml, group_vars/test.yml, etc.

Benefits

• Provides a clear and organized way to manage inventory and variables for different environments.
• Allows you to define environment-specific configurations in group variables, making it easy to customize settings for each environment.
• Simplifies playbook and Ansible role development, as you can use group variables to abstract environment-specific details from playbooks and roles.
• Unlocks the power of Ansible to manage environment differences effectively, efficiently, and intuitively.

Alternatives

While group-based environments is the recommended approach, alternatives exist. One older pattern suggested in past Ansible documentation involved creating multiple group_vars directories, one for each environment. This pattern only makes sense if environments are very different, which is rarely the case in practice. Managing differences across multiple directories requires constant use of external diff and merge tools, making it cumbersome.

In contrast, using a single group_vars directory enables a true GitOps approach, where environment differences are handled more effectively through environment groups and branching strategies. At this point, creating environment groups has become the standard method for managing environments in Ansible projects.

Another option is to use host variables for per-host customization. However, group variables are better for environment-wide settings to avoid repetition and improve maintainability.

Examples and Implementation

RWS Project

The RWS project environment group contains, as an example, only two environments (development, test). These files contain only one variable gs_env, with value development and test.

 group_vars/development.yml

---
gs_env: development

 group_vars/test.yml

---
gs_env: test

This project variable gs_env can now be used quite effectively to manage environment differences. To get a complete picture of how this is used, you could clone the project locally and then search for occurrences of the variable in the group_vars directory.

At this point, you can look at a specific example of how two project variables gs_ad_controller and gs_ad_controller_ip are used to ensure that a host joins the correct AD domain. See for more information the link below:

• Distinguish Between Ansible Engineering and Operations: Distinguish between Ansible engineering and operations as separate disciplines to ensure high-quality, maintainable automation.

PHX Project

The inventory project for the PHX project  c2platform/phx/ansible contains a more advanced example that introduces a project variable px_env for the environment but also an environment check.

 group_vars/all/env.yml

---
px_env: "{{ group_names | intersect(px_envs) | first }}"
px_envs: ['test', 'development']
px_envs_node: "{{ group_names | intersect(px_envs) }}"
px_envs_node_count: "{{ px_envs_node | length }}"
px_envs_check:
  name: >-
    Environment {{ inventory_hostname }} → {{ px_envs_node | join(', ') }}    
  type: fail
  msg: >-
    Node {{ inventory_hostname }} should be associated with exactly
    one environment group of: {{ px_envs | join(', ') }}!    
  when: "{{ px_envs_node_count != '1' }}"

This code snippet, defined in group_vars/all/env.yml, sets up environment variables and implements a validation check to ensure proper group assignments. Here’s a breakdown:

• px_env: Dynamically sets the environment by finding the intersection of the host’s group names with the allowed environments (px_envs). It selects the first (and expected only) match.
• px_envs: A list of allowed environment names, such as ’test’ and ‘development’.
• px_envs_node: Computes the intersecting environment groups for the current host.
• px_envs_node_count: Counts the number of intersecting environment groups.
• px_envs_check: Configures an Ansible fail module task. It defines a failure condition that triggers if a host is not associated with exactly one environment group from px_envs. This acts as a safeguard during playbook execution to prevent misconfigurations, with a custom error message explaining the issue.

Note, as shown below, that the inventory project still has an environment group file but the variable px_env is commented out. The file could be removed.

 group_vars/development.yml

---
# deprecated see group_vars/all/env.yml
# px_env: development

This setup ensures that each host belongs to exactly one environment group, promoting consistency and preventing errors in multi-environment setups.

Additional Information

For additional insights and guidance:

• Verify Environment Group Check: Verify and review the implementation of an environment check to ensure nodes are in exactly one environment group.
• Ansible Inventory Project: A structured collection of files used for managing hosts and configurations. It typically includes inventory files, playbooks, host configurations, group variables, and Ansible vault files.