configuration is created in the APIC, the controller
updates the logical model. It then performs the
intermediate step of creating a complete policy that it
pushes into all the switches, where the concrete model is
updated. The Cisco Nexus 9000 switches can only
execute the concrete model when running in ACI mode.
Each switch has a copy of the concrete model. If by any
chance, all the APIC controllers in a cluster go offline, the
fabric keeps functioning, but modifications to the fabric
policies are not possible.
The ACI policy model enables the specification of
application requirements. When a change is initiated to
an object in the fabric, the APIC first applies that change
to the policy model. This policy model change triggers a
change to the concrete model and the actual managed
endpoint. This management framework is called the
model-driven framework. In this model, the system
administrator defines the desired state of the fabric but
leaves the implementation up to the APIC. This means
that the data center infrastructure is no longer managed
in isolated, individual component configurations but
holistically, enabling automation and flexible workload
provisioning. In this type of infrastructure, network-
attached services can be easily deployed as the APIC
provides an automation framework to manage the
complete lifecycle of these services. As workloads move
and changes happen, the controller reconfigures the
underlying infrastructure to ensure that the policies are
still in place for the end hosts.
The Cisco ACI fabric is composed of physical and logical
components. These components are recorded in the
Management Information Model (MIM) and can be
represented in a hierarchical management information
tree (MIT). Each node in the MIT represents a managed