Agent Pack application and database agents manage the availability of an application. These agents start, stop, and monitor the application resources in a service group. When an agent detects a failure, the agent enables Veritas Cluster Server (VCS) to gracefully shut down the application and restart it on an available server. VCS then connects the application to the appropriate storage device and resumes normal operations.
The main components of an application or database agent are:
Agent functions: Agent functions are scripts or functions that agents call to manage a resource and to perform specific operations on a resource on behalf of the VCS cluster engine. For example, agents use functions to bring a resource online, to take a resource offline, or to monitor the resource.
For more information on agent functions, see the following page:
About agent functions.
For more information on the functions of a specific agent, see the installation and configuration guide for that agent.
Agent attributes: Every agent has a set of attributes. The values assigned to these attributes uniquely identify the application for which the resource is configured. These values determine the behavior of the resource the agent manages. Some attributes are required, while others are optional. Required attributes must be assigned values for the agent to function properly. If you do not specify a value for a required attribute, a default value is used.
For more information on specific agent attributes, see the installation and configuration guide for that agent.
Agent information XML file: Every agent has an XML file that contains information about the agent, such as the name and version of the agent and the description of the agent attributes. When a resource is configured using the Cluster Manager (Java Console), the XML file displays attribute information, such as descriptions, examples, and default values. The XML file also contains information that the Cluster Manager (Java Console) uses to allow or disallow certain operations on resources managed by the agent.
For more information about the agent information XML file, see the Veritas Cluster Server Agent Developer's Guide.
For more information about the Cluster Manager (Java Console), see the following page:
Resource types definition file: Every agent has its own 'types.cf' types definition file—a text file that represents the VCS configuration definition of the agent. The types.cf file defines the attribute types and the parameters that are passed to the VCS engine through the ArgList attribute.
For more information on the types.cf file, see the following page:
About the types.cf file
For information on how to import a types file for a specific agent, see the installation and configuration guide for that agent.
To see a sample types definition file for a specific agent, see the installation and configuration guide for that agent.
When an agent is started, it communicates with VCS through the agent framework and obtains the necessary configuration information from VCS. The agent also receives instructions regarding what action to take, if any are necessary, from the VCS engine. If any action is necessary, the agent calls the appropriate agent function to perform that action and returns the results of the action to the VCS engine. The agent then periodically monitors the resource or application and updates the VCS engine with the status.
For more information on the agent framework, see the following page:
High availability agents and the agent installation and configuration guides are available on the SORT website.