Replicas
--------

All charts must provide replica definitions and leverage those in the
Kubernetes manifests. This allows site operators to tune the replica
counts at install or when upgrading. Each chart should deploy with
multiple replicas by default to ensure that production deployments are
treated as first class citizens, and that services are tested with
multiple replicas more frequently during development and testing.
Developers wishing to deploy minimal environments can enable the
``development`` mode override, which should enforce only one replica per
component.

The convention today in OpenStack-Helm is to define a ``replicas:``
section for the chart, where each component being deployed has its own
tunable value.

For example, the ``glance`` chart provides the following replicas in
``values.yaml``

::

    replicas:
      api: 2
      registry: 2

An operator can override these on ``install`` or ``upgrade``:

::

    $ helm install local/glance --set replicas.api=3,replicas.registry=3