.. _resource-constraints:

=====================================
Resource Constraints in Kolla Ansible
=====================================

Overview
~~~~~~~~

Since the Rocky release it is possible to restrict
the resource usage of deployed containers.
The following components support this feature:

* Nova

In Kolla Ansible,
container resources to be constrained are referred to as dimensions.

The `Docker documentation <https://docs.docker.com/config/containers/resource_constraints/>`__
provides information on container resource constraints.
The resources currently supported by Kolla Ansible are:

.. code-block:: console

    cpu_period
    cpu_quota
    cpu_shares
    cpuset_cpus
    cpuset_mems
    mem_limit
    mem_reservation
    memswap_limit
    kernel_memory
    blkio_weight

.. end

Pre-deployment Configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Dimensions are defined as a mapping from a Docker resource name
(e.g. ``cpu_period``) to a string constraint value.

The variable ``default_container_dimensions`` sets the default dimensions
for all supported containers, and by default these are unconstrained.

Each supported container has an associated variable,
``<container name>_dimensions``, that can be used to set the resources
for the container. For example, dimensions for the ``nova_libvirt``
container are set via the variable ``nova_libvirt_dimensions``.

For example,
to constrain the number of CPUs that may be used by all supported containers,
add the following to the dimensions options section in
``/etc/kolla/globals.yml``:

.. code-block:: yaml

   default_container_dimensions:
     cpuset_cpus: "1"

.. end

For example, to constrain the number of CPUs that may be used by
the ``nova_libvirt`` container, add the following to the dimensions
options section in ``/etc/kolla/globals.yml``:

.. code-block:: yaml

   nova_libvirt_dimensions:
     cpuset_cpus: "2"

.. end

Deployment
~~~~~~~~~~

To deploy resource constrained containers, run the deployment as usual:

.. code-block:: console

  $ kolla-ansible deploy -i /path/to/inventory

.. end