Managing Dictionary Merging

Best practices for utilizing dictionary merging in Ansible inventory projects.

Projects: c2platform/ansible, c2platform/rws/ansbile-gis

Make sure you understand dictionary merging and variable precedence in C2 Platform Ansible projects.


In C2 Platform Ansible inventory projects , hash_behaviour = merge is the default setting. See for examples the ansible.cfg files in c2platform/ansible and c2platform/rws/ansbile-gis

However, users may encounter issues or confusion when merging dictionaries, because this is a more advanced Ansible feature. Clear guidance is needed to navigate this configuration effectively.


C2 Platform Ansible inventory projects are commonly configured with hash_behaviour = merge, allowing for flexible data structuring. Users often leverage roles like for Windows systems management but may need assistance in merging dictionaries seamlessly within this context.


Review and Document Inventory Structure

  • Examine your Ansible inventory projects and identify where hash_behaviour = merge is being applied.
  • Ensure your inventory structure is well-documented, and any use of merged dictionaries is clearly explained in comments.

Use Merging Sparingly

  • Only employ merging where necessary, typically for host or group variables requiring merging.
  • Avoid unnecessary merging, as it can lead to complexity and unintended consequences.

Define Default Values Thoughtfully

  • When merging dictionaries, define default values that are meaningful and compatible with specific data.
  • Consider how defaults will interact with specific values during merging.

Test Playbooks Rigorously

  • Thoroughly test playbooks to ensure merged dictionaries behave as expected.
  • Verify that merged data produces the desired results and doesn’t introduce unexpected issues.

Understand Variable Precedence

  • Familiarize yourself with Ansible’s variable precedence rules.
  • Be aware of how variables defined at different levels (e.g., host, group, playbook) interact when merged.

Monitor and Document Changes

  • Periodically review your inventory and configurations, documenting any changes.
  • Communicate changes to your team members to maintain transparency and consistency.

Handle Key Conflicts

  • Be prepared to address conflicts when the same key exists in multiple dictionaries being merged.
  • Document your approach to resolving such conflicts.

Respect Data Security

  • If you’re merging dictionaries containing sensitive data, exercise extreme caution.
  • Use Ansible Vault or other encryption methods to protect sensitive information and use only simple string variables in a vault.

Example and implementation

See the Ansible role  Ansible role. in the c2platform.wincore Ansible collection for examples on how merging is used.