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Chapter 8. Management
Management features are the final aspect of the Web services architecture to describe. These features are defined in the WS-Management specification [WS-Management].WS-Management builds on several components of the architecture, providing a common set of operations that are required by all systems management solutions. This includes the ability to discover the presence of management resources and navigation among them. Individual management resources, such as settings and dynamic values, can be retrieved, set, created, and deleted. The contents of containers and collections, such as large tables and logs, can be enumerated. Finally, event subscriptions and specific management operations are defined. In each of these areas, WS-Management defines only minimal implementation requirements.Care has been taken so that conformant WS-Management implementations can be deployed to small devices. At the same time, the specification has been designed to scale up to large datacenter and distributed installations. In addition, mechanisms are defined independent of any implied data models or system health models. This independence supports the specification's application to all kinds of Web services.WS-Management requires that managed resources be referenced using endpoint references with specific additional information. This information includes the URL of the agent that provides access to the resource, the unique identifier URI of the resource type that the resource belongs to, and zero or more keys that identify the resource. These keys are assumed to be name/value pairs. The mapping of this information to a WS-Addressing endpoint reference is as follows: the URL of the resource is mapped to the address property, the resource type identifier is mapped to a specific reference property named ResourceURI (in the appropriate XML namespace), and each key is mapped to a reference parameter named Key with an attribute called Name.To accommodate the messaging needs of management services, three qualifiers are defined for the operations. The SOAP representation of these qualifiers is in header elements. An "operation timeout" specifies a deadline after which the operation need not be serviced. The "locale" element is used when translations of the underlying information are needed or expected. Finally, a "freshness" qualifier is provided to request up-to-date values and prohibit returning stale data.For data access using the WS-Transfer operations, WS-Management specifies three more qualifiers. The Get operation can be qualified with the SummaryPermitted header and the NoCache header. The SummaryPermitted qualifier enables transmission of abbreviated representations, when available. The NoCache qualifier requires transmission of fresh data, disallowing caching of the information. For the Put and Create operations, the ReturnResource qualifier mandates that the service return the new representation of a resource in the message response. ReturnResource allows resource-constrained Web services to avoid retaining state information when updating a resource.WS-Management defines three custom delivery modes for event notification: batched, pull, and trap. Each of these modes is identified by a URI. These URIs are used when establishing subscriptions. The batched delivery mode enables a subscriber to receive multiple event messages bundled in single SOAP messages. The subscriber can also request a maximum number of events included in the bundle, a maximum amount of time that the service should take accumulating events, and a maximum amount of data that should be returned. The pull delivery mode allows the data-producing service to maintain a logical queue of events so that the subscriber can poll for notifications on-demand. This polling is done using WS-Enumeration with an enumeration context returned with the subscription response message. Finally, when UDP multicast is an appropriate messaging mechanism, the trap delivery mode allows an event source to use it. In trap mode, the event source can send its notifications to a predetermined UDP multicast address.
