Cisco Unified Communications Manager System Guide, Release 9.1(1)
Clustering
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Clustering

Clustering

This chapter provides information about the clustering feature of Cisco Unified Communications Manager which provides a mechanism for distributing call processing and database replication amongst multiple Cisco Unified Communications Manager servers that run the exact same version of Cisco Unified Communications Manager. Clustering provides transparent sharing of resources and features and enables system scalability.

Configure cluster

This topic provides an overview of the steps that are required to install and configure a Cisco Unified Communications Manager cluster, which comprises a set of Cisco Unified Communications Manager servers that share the same database and resources.

Procedure
    Step 1   Gather the information that you need to install Cisco Unified Communications Manager and any other software applications on the first node and subsequent servers. Also, determine how you will allocate the servers in the cluster.
    Step 2   Install the database server (first node).

    See the installation documentation for the hardware components that you are installing.

    Step 3   Install Cisco Unified Communications Manager and any additional software applications on the subsequent servers.
    Note    Before installing the subsequent servers, you must define the nodes in the Server Configuration window in Cisco Unified Communications Manager Administration.
    Step 4   Configure device pools and use them to assign specific devices to a Cisco Unified Communications Manager group.
    Step 5   If you are using an intercluster trunk, install and configure it as an intercluster trunk, either gatekeeper-controlled or non-gatekeeper-controlled.
    Step 6   If you want to provide call admission control for an intercluster trunk, configure either a gatekeeper-controlled intercluster trunk or Cisco Unified Communications Manager locations.

    Clusters

    A cluster comprises a set of Cisco Unified Communications Manager servers that share the same database and resources. You can configure the servers in a cluster in various ways to perform the following functions:

    • Database replication
    • TFTP server
    • Application software server

    You can use various nodes in the cluster for call-processing redundancy and for load balancing.

    You can activate feature services on various nodes in the cluster to specify which servers perform certain functions for the cluster. By accessing the Service Activation window in Cisco Unified Serviceability, you can dedicate a particular server to one function or combine several functions on one server, depending on the size of your system and the level of redundancy that you want.


    Tip


    The Restart Cisco Communications Manager on Initialization Exception service parameter determines whether the Cisco CallManager service restarts if an error occurs during initialization. This parameter defaults to TRUE and, with this value, the Cisco Communications Manager initialization aborts when an error occurs during initialization. Setting the value to FALSE allows initialization to continue when an error is encountered. You can locate this clusterwide parameter in the


    Database replication in a cluster

    A cluster comprises a set of Cisco Unified Communications Managers servers that share a common database. When you install and configure Cisco Unified Communications Manager, you specify which servers belong to the same cluster. A cluster comprises the first node (publisher) and subsequent nodes (subscribers). The first node in a cluster contains the Cisco Unified Communications Manager database, which gets automatically installed when you install Cisco Unified Communications Manager on the first node. Cisco Unified Communications Manager uses all subsequent nodes in the cluster for database replication. After you add the subsequent node to the Server Configuration window in Cisco Unified Communications Manager Administration and install Cisco Unified Communications Manager on the subsequent node, the node contains a replicate of the database that exists on the first node.

    After you add, update, or delete configuration in Cisco Unified Communications Manager Administration, Cisco Unified Serviceability, or Cisco Unified CM User Options, Cisco Unified Communications Manager writes the configuration update to the Cisco Unified Communications Manager database on the first node in the cluster and then updates the database replicates on the subsequent nodes. If both the first node and subsequent nodes are available, you read and write configuration data in the GUIs on the first node, even when you browse to GUIs on the subsequent node(s) in the cluster. If the first node is unavailable, you can read configuration data in the GUIs on the subsequent node(s), but you cannot make updates in the GUIs on the subsequent nodes.

    Consider the following information that is related to Cisco Unified Communications Manager database replication:

    • Before you install Cisco Unified Communications Manager on the subsequent node, you must add the subsequent node to the Server Configuration window by accessing Cisco Unified Communications Manager Administration on the first node. For more information on adding a subsequent node to Cisco Unified Communications Manager Administration, see Balanced call processing.
    • For Cisco Unified Communications Manager database replication to occur, you must install the exact same version of Cisco Unified Communications Manager on the first node and subsequent node(s) in the cluster.
    • Do not make configuration changes (additions, updates, or deletions) during a Cisco Unified Communications Manager upgrade. If you make configuration changes during an upgrade, you may cause data to be lost or cause data not to replicate; in addition, the upgrade may fail.
    • You can view the Unified CM Cluster Overview report in Cisco Unified Reporting to determine how all nodes are classified in the database; that is, if the node serves as the first (publisher) or a subsequent (subscriber) node. Likewise, you can click the Host Name/IP Address link in the Find and List Servers window in Cisco Unified Communications Manager Administration; after the Server Configuration window displays, you can view the read-only Database Replication field. If the field displays Publisher, the node serves as the first node. If the field displays Subscriber, the node serves as a subsequent node.
    • Changing the name or IP address of a node in a cluster impacts Cisco Unified Communications Manager database replication. Before you change the name or IP address of a node, review the document, Changing the IP Address and Host Name for Cisco Unified Communications Manager Release 8.5(1).
    • To verify the state of Cisco Unified Communications Manager database replication, for example, whether replication is occurring, broken, and so on, you can use the Real-Time Monitoring Tool, Cisco Unified Reporting, or the Command Line Interface (CLI).
    • If you determine that a problem exists with Cisco Unified Communications Manager database replication, you can repair database replication via the Command Line Interface (CLI).
    • If you revert to a previous version of Cisco Unified Communications Manager, you must reset Cisco Unified Communications Manager database replication via the Command Line Interface (CLI) after you revert to the previous version.

    Intercluster communication

    In very large environments, you might need to configure more than one cluster to handle the call-processing load. Communication between the clusters typically occurs by means of intercluster trunks or gatekeeper trunks. Most large systems use one of two main types of multicluster configurations:

    • Large, single campus, or metropolitan-area network (MAN)
    • Multisite WAN with distributed call processing (one or more Cisco Unified Communications Managers at each site)

    Because intercluster trunks in a MAN usually have sufficient bandwidth, they do not require any call admission control mechanism. Multisite WANs with distributed call processing typically use gatekeeper technology for call admission control.

    Intracluster Communication

    Cisco Unified Communications Manager also supports intracluster communication, which is a multisite WAN with centralized call processing (no Cisco Unified Communications Manager at the remote site or sites). Multisite WANs with centralized call processing use the locations feature in Cisco Unified Communications Manager to implement call admission control.

    Most features of Cisco Unified Communications Manager do not extend beyond a single cluster, but the following features do exist between clusters:

    • Basic call setup
    • G.711 and G.729 calls
    • Multiparty conference
    • Call hold
    • Call transfer
    • Call park
    • Calling line ID

    For more information about intercluster communication and call admission control, see Cisco Unified Communications Solution Reference Network Design (SRND).

    Balanced call processing

    After installing the Cisco Unified Communications Managers that form a cluster, you should, as much as possible, evenly balance the call-processing load across the system by distributing the devices (such as phones, gateways, CTI route points, CTI ports, and route lists) among the various Cisco Unified Communications Managers in the cluster. To distribute the devices, you configure Cisco Unified Communications Manager groups and device pools and then assign the devices to the device pools in a way that achieves the balance that you want.

    Cisco Unified Communications Manager groups and device pools represent logical groupings of devices that you can arrange in any way that you want. For ease of administration, make sure that all the devices in a group or pool share a common and easily identified characteristic, such as their physical location on the network.

    You can also use Cisco Unified Communications Manager groups to establish redundancy (backup call processors) for the primary Cisco Unified Communications Manager in the group. A Cisco Unified Communications Manager group comprises an ordered list of up to three Cisco Unified Communications Manager servers. During normal operation, the first (primary) Cisco Unified Communications Manager in the group controls all device pools and devices that are assigned to that group. If the primary Cisco Unified Communications Manager in a group fails, control of the device pools and devices that are registered with the primary Cisco Unified Communications Manager transfers to the next Cisco Unified Communications Manager in the group list.

    For example, assume a simplified system that comprises three Cisco Unified Communications Managers in a cluster, with 300 existing Cisco Unified IP Phones and provisions to auto-register new phones as they are added later.

    • The configuration includes four Cisco Unified Communications Manager groups: group G1 that is assigned to device pool DP1, group G2 that is assigned to device pool DP2, group G3 that is assigned to device pool DP3, and group G4 that is assigned to device pool DP4. Group G4 serves as the default group for devices that auto-register.
    • Unified CM1 serves as the primary Cisco Unified Communications Manager for the devices in DP1 and DP2, first backup for DP3, and second backup for the devices in DP4.
    • Unified CM2 serves as the primary Cisco Unified Communications Manager for the devices in DP3 and DP2, first backup for DP1, and second backup for the devices in DP2.
    • Unified CM3 serves as the first backup Cisco Unified Communications Manager for the devices in DP2 and DP4 and second backup for the devices in DP1 and DP3.