Brokering Planning Metadata in a P2P Environment

In self-adaptive systems, metadata about resources in the system (

e.g.

, services, nodes) must be dynamically published, updated, and discarded. Current adaptive middleware approaches use statically configured, centralized repositories for storing and retrieving of such metadata. In

peer-to-peer

(P2P) environments, we can not assume the existence of server nodes that are always available for hosting such centralized services. However, the metadata repository is the keystone of the adaptation middleware and the consistency of adaptations relies on its reliability.

To address this limitation in our QuA planning-based adaptation middleware, we introduce a P2P broker, which is a metadata advertisement service based on P2P technology. This P2P broker can be plugged into the QuA middleware to support the construction of self-adaptive applications in a P2P environment. We use a structured P2P protocol that distributes the service metadata over a set of nodes based on service type and property information. The P2P broker is therefore capable of handling node failures by providing replication of the metadata. We present a working prototype of the P2P broker as well as results from initial experiments. These results show that the metadata distributes well over the nodes in the network, thus enabling scalability and robustness to node failures.