Cloud Federation and Distribution

ions There are several traditional abstractions for programming distributed applications in general, which also play a role in cloud datacenter communication: ● Sockets: these are typical for programming unicast interaction (one-to-one) as well as simple one-to-many interaction ● Publish/subscribe: this is a common high-level abstraction for multicasting. Producers are termed ​publishers​ and consumers ​subscribe​ to specific messages. Figure 7 illustrates entities of a publish/subscribe system. Several variants for outlining messages of interest can be distinguished: o Topic-based publish/subscribe (TPS): here, publishers explicitly post messages under specific ​topics​, whilst subscribers delineate topics of interest. Topics can exhibit a “flat” name-space or be in different relationships to each other such as hierarchical. o Content-based publish/subscribe (CPS): here subscriptions are expressed based on predicates on message content ("filters"). Most systems thus support messages with some form of property-value pairs which are used for filtering. ● Message queuing: these systems are the most common implementation of one-of-many communication. Typically consumers pull messages from queues, but this can also be replaced by push-style communication. Sockets typically are bound to IP addresses, which given the problems with such addresses outside of clouds makes them unsuited for inter-cloud communication.