===========
Hierarchies
===========

One of the most common patterns of the operators is to create
children objects in the same Kubernetes cluster.
Kopf provides some tools to simplify connecting these objects together.

.. note::

    Kopf is not a Kubernetes client library.
    It does not provide any means to manipulate the Kubernetes objects
    or to talk to the Kubernetes API.
    Use any of the existing libraries for that purpose,
    such as the official `kubernetes client`_ or pykube-ng_.

.. _kubernetes client: https://github.com/kubernetes-client/python
.. _pykube-ng: https://github.com/hjacobs/pykube


Labelling
=========

To mark the created objects with labels::

    kopf.label(obj, {'label1': 'value1', 'label2': 'value2')

To mark it with the same labels as another (e.g. parent) object:

    kopf.label(objs, labels=owner.get('metadata', {}).get('labels', {}))

Where ``obj`` or ``objs`` is either a dict of the object fields,
or a list/tuple of dicts with multiple objects.


Owner references
================

Kubernetes natively supports the owner references, when one object (child)
can be marked as "owned" by one or more other objects (owners or parents).

if the owner is deleted, its children will be deleted too, automatically,
and not additional handlers are needed.

To mark an object or objects as owned by another object::

    kopf.append_owner_reference(objs, owner=owner)

To unmark::

    kopf.remove_owner_reference(objs, owner=owner)

.. seealso::
    :doc:`walkthrough/deletion`.


Name generation
===============

If the object has its ``metadata.name`` field set, that name will be used.

Alternatively, the operator can request Kubernetes to generate the name
with the specified prefix and random suffix.
This is done by setting ``metadata.generateName`` field.

This is commonly used for the parent objects that orchestrate multiple
children objects of the same kind (e.g. as pods in the deployment).


Same namespaces
===============

Usually, it is expected that the children objects are created in the same
namespace as their parent (unless there are strong reasons to do differently).


Adopting
========

All of the above can be done in one call::

    kopf.adopt(obj, owner=owner)
    kopf.adopt([obj1, obj2], owner=owner)
