Resource Management Object Model

This section and its subsections introduce some fundamental terminology and explain how the different elements of the API are put together to create a highly available application.

The RGM and its associated API handle three major kinds of interrelated objects: resource types, resources, and resource groups. One way to introduce these objects is by means of an example, such as the following.

A developer could implement a resource type, ha-oracle, which makes an existing Oracle DBMS application highly available. An end user might define separate databases for marketing, engineering, and finance, each of which would be a resource of type ha-oracle. The cluster administrator could place these resources in separate resource groups so they could run on different nodes and fail over independently. Likewise, a developer could create a second resource type, ha-calendar, to implement a highly available calendar server that requires an Oracle database. The cluster administrator could place the resource for the finance calendar into the same resource group as the finance database resource so that both resources would run on the same node and fail over together.

Resource Types

A resource type consists of a software application to be run on the cluster, control programs used as callback methods by the RGM to manage the application as a cluster resource, and a set of properties that form part of the static configuration of a cluster. The RGM uses resource type properties to manage resources of a particular type.

In addition to a software application, a resource type can represent other system resources such as network addresses.

The resource type developer specifies the properties for the resource type and sets their values in a resource type registration (RTR) file. The resource type registration file follows a well-defined format described in "Setting Resource and Resource Type Properties" and in the rt_reg(4) man page. See also "Defining the Resource Type Registration File" for a description of a sample resource type registration file.

Table A-1 provides a list of the resource type properties.

The cluster administrator installs the resource type implementation and underlying application on a cluster and registers it using administrative commands. The registration procedure enters into the cluster configuration the information from the resource type registration file. The Sun Cluster 3.0 Data Services Installation and Configuration Guide describes the procedure for registering a data service.

Resources

A resource inherits the properties and values of its resource type. In addition, a developer can declare resource properties in the resource type registration file. See Table A-2 for a list of resource properties.

The cluster administrator can change the values of certain properties depending on how they were specified in the resource type registration (RTR) file. For example, property definitions can specify a range of allowable values and specify when the property is tunable, for example, at creation, anytime, or never. Within these specifications, the cluster administrator can make changes to properties using administration commands.

The cluster administrator can create many resources of the same type, each resource having its own name and set of property values, so that more than one instance of the underlying application can run on the cluster. Each instantiation requires a unique name within the cluster.

Resource Groups

Each resource must be configured in a resource group. The RGM brings all resources in a group online and offline together on the same node. When the RGM brings a resource group online or offline, it invokes callback methods on the individual resources in the group.

The nodes on which a resource group is currently online are called its primaries or primary nodes. A resource group is mastered by each of its primaries. Each resource group has an associated Nodelist property, set by the cluster administrator, which identifies all potential primaries or masters of the resource group.

A resource group also has a set of properties. These properties include configuration properties that can be set by the cluster administrator and dynamic properties, set by the RGM, that reflect the active state of the resource group.

The RGM defines two types of resource groups, failover and scalable. A failover resource group can be online on one node only at any time while a scalable resource group can be online on multiple nodes simultaneously. The RGM provides a set of properties to support the creation of each type of resource group. See "Implementing a Failover Resource" and "Implementing a Scalable Resource" for details on these properties.

See Table A-3 for a list of resource group properties.