reconstructed

An Ansible plugin that can generate structured inventories programmatically.

This is a work in progress. I will make this README more useful later, provided I just don't forget about this whole thing.

A reconstructed inventory executes a list of instructions that is read from the instructions YAML field. Each instruction is a table with some minimal control flow (when, loop and run_once keywords that work mostly like their playbook cousins), an action field that contains the name of the instruction to execute, and whatever fields are needed for the instruction.

The following actions are supported:

• create_group creates a group. The name of the group must be provided using the group field, which must be a valid name or a Jinja template that evaluates to a valid name. In addition, a parent field containting the name of a single, existing parent group (or a Jinja template generating the name) may be provided. Finally, the add_host field may be set to a truthy value if the current host must be added to the new group.

• add_child adds a child group to another group. The name of the group being added must be provided in the child entry, while the name of the parent must be provided in the group entry. Both groups must exist. In addition, the names may be specified using Jinja templates.

• add_host adds the current inventory host to a group. The name of the group must be provided in the group entry. The group must exist.

• fail causes the computations for the current host to stop with an error. The error message may be specified in the message entry; if present, it will be evaluated using Jinja.

• set_fact and set_var create a fact and a local variable, respectively. Local variables will only be kept during the execution of the script for the current host, while facts will be added to the host's data. The name entry specifies the name of the fact or variable while the value entry specifies its value. Both may be Jinja templates.

• stop stops processing the list of instructions for the current host.

In addition, the block can be used to repeat multiple instructions or make them obey a single conditional. The instruction must include a block field, containing the list of instructions which are part of the block. It may have a rescue field, containing a list of instructions which will be executed on error, and always, which may contain a list of instructions to execute in all cases.

If the vars field is defined on an instruction, it must contain a table of local variables to define. Their values are computed after the loop variable is evaluated, but before the condition is. If these variables already existed, their state will be saved and they will be restored after the instruction is done executing. This is different from the core Ansible behaviour, which does not evaluate the vars unless they are used.

A somewhat silly example can be found in the example directory. Trying to execute it using ansible-inventory --graph results in the following output.

[WARNING]: reconstructed - error on host evil-vm: evil-vm is obviously evil,
skipping.
@all:
  |--@managed:
  |  |--@by_environment:
  |  |  |--@env_dev:
  |  |  |  |--vm00
  |  |  |  |--vm01
  |  |  |  |--vm02
  |  |  |  |--vm03
  |  |  |  |--vm04
  |  |  |  |--vm09
  |  |  |--@env_prod:
  |  |  |  |--vm05
  |  |  |  |--vm06
  |  |  |  |--vm07
  |  |  |  |--vm08
  |  |--@by_failover_stack:
  |  |  |--@fostack_1:
  |  |  |  |--vm00
  |  |  |  |--vm02
  |  |  |  |--vm05
  |  |  |  |--vm07
  |  |  |--@fostack_2:
  |  |  |  |--vm01
  |  |  |  |--vm03
  |  |  |  |--vm06
  |  |  |  |--vm08
  |  |  |--@no_failover:
  |  |  |  |--vm04
  |  |  |  |--vm09
  |  |--@by_network:
  |  |  |--@net_dev:
  |  |  |  |--vm00
  |  |  |  |--vm01
  |  |  |  |--vm02
  |  |  |  |--vm03
  |  |  |  |--vm04
  |  |  |--@net_infra:
  |  |  |  |--vm05
  |  |  |  |--vm06
  |  |  |  |--vm07
  |  |  |  |--vm08
  |  |  |  |--vm09
  |  |--@by_service:
  |  |  |--@svc_ldap:
  |  |  |  |--@svcm_ldap_back:
  |  |  |  |  |--@svcm_ldap_ro:
  |  |  |  |  |  |--vm02
  |  |  |  |  |  |--vm03
  |  |  |  |  |  |--vm07
  |  |  |  |  |  |--vm08
  |  |  |  |  |--@svcm_ldap_rw:
  |  |  |  |  |  |--vm04
  |  |  |  |  |  |--vm09
  |  |  |  |--@svcm_ldap_front:
  |  |  |  |  |--vm00
  |  |  |  |  |--vm01
  |  |  |  |  |--vm05
  |  |  |  |  |--vm06
  |--@reedmably_evil:
  |  |--evil-but-nicer-vm
  |--@ungrouped:
  |  |--evil-vm
  |  |--localhost