ansible_hostworks

• Purpose

  • generate an Ansible inventory using a list of hosts and a parsing template
  • inventory is in INI

• Definitions

  • host file: file that is a list of hosts to be parsed
  • template: a YAML template that uses regexp to parse a list of hosts

• Usage

  • define a list of hosts in a file, as in test_hosts
  • define a template, as in test_template.yml
  • run:

    python inventory_generator.yml --hosts='<host file>' --template='<YAML template file>'

  • test resulting inventory:

    ansible -m ping -i <resulting inventory as file> all

• Description

  • the template YAML file is parsed into a template dict
  • one template dict becomes one group in the resulting inventory

  • template dict == group (in inventory)

  • the dict has a structure similar to (almost identical to) an Ansible YAML inventory
  • the parser is defined in GroupWorks.py
  • parsing
    • the "children" key
      • in Ansible inventory, a group YAML object has a key named "children", which is a set of groups
      • similarly, a template dict has a key named "children" that is a set (dict) of templates
    • the "hosts" key
      • defines which hosts are present in a group
      • a child templates hosts are a subset of its parent's hosts
      • i.e. the hosts key narrows the entire set of hosts when parsing recurses
  • when the parser finishes defining a group, it will recurse on the template's children to create child groups
  • the parser handles the INI parent child relation (e.g. creates [all:children] using children defined in "all" template)

• Technicalities

  • Group objects
    • defined in Group.py
    • will not copy hosts, rather they point to a list of hosts
    • therefore, if a list of hosts is defined, then passed to a Group object, changing that list will change the list for the Group object
    • this is desireable for now, because if multiple groups rely on a host in one list, then changing that host will change it in each Group that references it
  • Capture groups
    • only the first match in a regex pattern is used as the name for the (child) groups generated by regex by the parser
    • to work around this limitation, nest child group regexp in a group defined by literal name
    • (TODO) other workarounds are under work

• testing:

  • https://regex101.com
  • use the Python flavor