The Application Policy Infrastructure Controller is the main architectural component of the Cisco ACI solution. The APIC is the unified point of automation and management for the Cisco ACI fabric, policy enforcement, and health monitoring. The controller optimizes performance and manages and operates a scalable multitenant Cisco ACI fabric.

The APIC appliance or virtual machine is deployed as a cluster. A minimum of three infrastructure controllers are configured in a cluster to provide control of the scale-out Cisco ACI fabric (see Figure 4-2). The ultimate size of the controller cluster is directly proportionate to the size of the Cisco ACI deployment and is based on the transaction-rate requirements. Any controller in the cluster can service any user for any operation, and a controller can be transparently added to or removed from the cluster.

Figure 4-2 Cisco ACI Fabric

The APIC cluster is composed of multiple APIC controllers that provide operators a unified real-time monitoring, diagnostic, and configuration management capability for the ACI fabric. To assure optimal system performance, follow these general guidelines for making changes to or managing the APIC cluster:

Cisco recommends that you have at least three active APICs in a cluster, along with additional standby APICs. A cluster size of three, five, or seven APICs is recommended. A cluster size of four or six APICs is not recommended.

Disregard cluster information from APICs that are not currently in the cluster; they do not provide accurate cluster information.

Cluster slots contain an APIC ChassisID. After you configure a slot, it remains unavailable until you decommission the APIC with the assigned ChassisID.

If an APIC firmware upgrade is in progress, wait for it to complete and the cluster to be fully fit before proceeding with any other changes to the cluster.

When moving an APIC, first ensure that you have a healthy cluster. After verifying the health of the APIC cluster, choose the APIC you intend to shut down. After the APIC has shut down, move the APIC, reconnect it, and then turn it back on. From the GUI, verify that all the controllers in the cluster return to a fully fit state.