Global Cluster Management

VCS enables you to perform operations (online, offline, switch) on global service groups from any system in any cluster using the VCS command-line interface, the Java Console, or the Web Console. See User Privileges in Global Clusters for information about the privileges required for global operations.

You can bring service groups online or switch them to any system in any cluster. If you do not specify a target system, VCS uses the FailOverPolicy to determine the system. Deciding Startup and Failover Locations for more information.

Management of remote cluster objects is aided by inter-cluster communication enabled by the wide-area connector (wac) process.

Wide-Area Connector Process

The wide-area connector (wac) is a failover Application resource that ensures communication between clusters.

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The wac process runs on one system in each cluster and connects with peers in remote clusters. It receives and transmits information about the status of the cluster, service groups, and systems. This communication enables VCS to create a consolidated view of the status of all the clusters configured as part of the global cluster. The process also manages wide-area heartbeating to determine the health of remote clusters. The process also transmits commands between clusters and returns the result to the originating cluster.

Wide-Area Heartbeats

The wide-area Heartbeat agent manages the inter-cluster heartbeat. Heartbeats are used to monitor the health of remote clusters. For a list of attributes associated with the agent, see Heartbeat Attributes. You can change the default values of the heartbeat agents using the hahb -modify command.

Sample Configuration

Serialization–The Authority Attribute

VCS ensures that multi-cluster service group operations are conducted serially to avoid timing problems and to ensure smooth performance. The Authority attribute prevents a service group from coming online in multiple clusters at the same time. Authority is a persistent service group attribute and it designates which cluster has the right to bring a global service group online. The attribute cannot be modified at runtime.

A two-phase commit process prevents timing issues. If two administrators simultaneously try to bring a service group online in a two-cluster global group, one command is honored, and the other is rejected.

The attribute prevents bringing a service group online in a cluster that does not have the authority to do so. If the cluster holding authority is down, you can enforce a takeover by using the command hagrp -online -force service_group. This command enables you to fail over an application to another cluster when a disaster occurs.

You must seed authority if it is not "held" on any cluster.

Offline operations on global groups can originate from any cluster and do not require a change of authority to do so, because taking a group offline does not necessarily indicate an intention to perform a cross-cluster failover.

Authority and AutoStart

The attributes Authority and AutoStart work together to avoid potential concurrency violations in multi-cluster configurations.

If the AutoStartList attribute is set, and if a group's Authority attribute is set to 1, HAD waits for the wac process to connect to the peer. If the connection fails, it means the peer is down and the AutoStart process proceeds. If the connection succeeds, HAD waits for the remote snapshot. If the peer is holding the authority for the group and the remote group is online (because of takeover), the local cluster does not bring the group online and relinquishes authority.

If the Authority attribute is set to 0, AutoStart is not invoked.

Resiliency and "Right of Way"

VCS global clusters maintain resiliency using the wide-area connector process and the ClusterService group. The wide-area connector process runs as long as there is at least one surviving node in a cluster.

The wide-area connector, its alias, and notifier are components of the ClusterService group, described in The ClusterService Group.

VCS Framework

VCS agents now manage external objects that are part of wide-area failover. These objects include replication, DNS updates, and so on. These agents provide a robust framework for specifying attributes and restarts, and can be brought online upon fail over.

New Entry Points

New entry points, action and info, allow for detailed management of cluster and replication-related objects. See the VERITAS Cluster Server Bundled Agents Reference Guide and the VERITAS Cluster Server Agent Developer's Guide for more information.

DNS Agent

The DNS agent updates the canonical name-mapping in the domain name server after a wide-area failover. See the VERITAS Cluster Server Bundled Agents Reference Guide for more information about the agent.

RVG Agent

The RVG agent manages the Replicated Volume Group (RVG). Specifically, it brings the RVG online, monitors read-write access to the RVG, and takes the RVG offline. Use this agent when using VVR for replication.

RVGPrimary agent

The RVGPrimary agent attempts to migrate or take over a Secondary to a Primary following an application failover. The agent has no actions associated with the offline and monitor routines.

RVGSnapshot Agent

The RVGSnapshot agent, used in fire drill service groups, takes space-optimized snapshots so that applications can be mounted at secondary sites during a fire drill operation.