tpaexec eval
============

You can use the eval command to evaluate an arbitrary Jinja/Ansible
expression in the context of the cluster’s inventory. The information
can be related to variables, inventory, gathered OS facts, computed
paths, package names, etc.

Usage
-----

- Run ``tpaexec eval ~/clusters/speedy '<expression>'``

Options
^^^^^^^

- ``tpaexec eval ~/clusters/speedy '<expression>' --hosts <pattern>``

Restrict evaluation to a host pattern. The pattern can be a single
instance name (``unreal`` ), a colon-separated list (``unreal:ultra`` ),
``localhost`` , or a group name (``role_primary`` , ``role_etcd`` ).

- ``tpaexec eval ~/clusters/speedy '<expression>' --no-init``

Skip the cluster initialisation playbook. Only variables derived from
``config.yml`` and the generated inventory are available; ``ansible_*``
host facts will be undefined. Recommended for quick inventory
inspection.

Example Output
--------------

Look up a value from ``config.yml`` for a single host:

.. code:: shell

   tpaexec eval ~/clusters/speedy {{ postgres_version }} --no-init --hosts unreal

.. code:: output

     unreal => {
       "msg": "17"
   }

Print a value for every host in the cluster:

.. code:: shell

   tpaexec eval ~/clusters/speedy {{ ip_address }} --no-init

.. code:: output

     unreal => {
       "msg": "10.33.155.2"
   }
     ultra => {
       "msg": "10.33.155.3"
   }
     quondam => {
       "msg": "10.33.155.4"
   }

Inspect inventory-wide data by targeting ``localhost`` :

.. code:: shell

   tpaexec eval ~/clusters/speedy {{ groups.keys() | list }} --no-init --hosts localhost

.. code:: output

     localhost => {
       "msg": [
           "all",
           "ungrouped",
           "tag_Cluster_speedy"
       ]
   }

List every variable defined for a host (useful when you don’t yet know
the name of the variable you want):

.. code:: shell

   tpaexec eval ~/clusters/speedy {{ hostvars[inventory_hostname].keys() | list | sort }} --no-init --hosts unreal

.. code:: output

     unreal => {
       "msg": [
           "ansible_user",
           "backup",
           "cluster_name",
           "failover_manager",
           "ip_address",
           "postgres_version",
           "role",
           "..."
       ]
   }

Read a fact gathered from the host itself (omit ``--no-init`` so the
initialisation playbook runs and populates ``ansible_*`` facts):

.. code:: shell

   tpaexec eval ~/clusters/speedy {{ ansible_distribution }} --hosts unreal

.. code:: output

     unreal => {
       "msg": "Debian"
   }