Messages as the unifying mechanism: Messages are the most unifying factor among disparate and distributed cloud services. The goals of cloud service integration get accomplished through message passing. The following section lists and details the various service message patterns. Service messages can be authenticated, routed, enriched, filtered, secured, and composed in order to fulfill the expectations of federated clouds. Cloud intermediation and remediation can be performed through smart messaging. Path-breaking and hitherto unknown services can be built and deployed through the innovative usage of service messages.
How do different distributed and decentralized cloud services find, bind, access, and collaborate with one another in a loosely coupled as well as decoupled manner?
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Problem |
Services can be run on one virtual machine or in different virtual machines within a cloud environment. Services can even be run on geographically distributed clouds. There are public, private, and hybrid clouds and there are a few communication protocols. The conventional protocols induce a possibility of tight coupling between services. These, in turn, impose certain restrictions on service reusability, testability, and modifiability. |
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Solution |
Going forward, loose coupling and decoupling are the viable and valuable solution approaches. As even loose coupling has some constraints, decoupling among services is being touted as the most promising solution, and messaging is the way forward for establishing decoupled communication, which in turn eliminates the drawbacks of traditional communication methods |
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Impacts |
Messaging technology brings a few QoS concerns, such as reliable delivery, security, performance, and transactions. |
Problem: Different applications usually use different languages, data formats, and technology platforms. When one application (component) needs to exchange information with another one, the format of the target application has to be respected. Sending messages directly to the target application results in a tight coupling of sender and receiver since format changes directly affect both implementations. Also, direct sending tightly couples the applications regarding the addresses by which they can be reached.
Cloud applications and services communicate using a variety of protocols. Remote procedure call (RPC), remote method invocation (RMI), Windows Communication Framework (WCF), and service protocols (SOAP and REST over HTTP) are some of the leading mechanisms for cloud resources to connect and collaborate purposefully. However, all these lead to a kind of tight coupling, which in turn becomes a hitch or hurdle for services to seamlessly and spontaneously cooperate to achieve bigger and better things. The urgent requirements are therefore loose coupling and decoupling. How can cloud application services communicate remotely through messages while being loosely coupled regarding their location and message format? Another brewing requirement is to enable complete decoupling among services.
Solution: The context is that distributed applications or their service components exchange information using messaging. Messaging comes as a viable alternative communication scheme that does not rely on persistent connections. Instead, messages are being transmitted as independent units of communication routed through the underlying infrastructure. That is, simply connect applications through an intermediary; the message-oriented middleware hides the complexity of addressing and availability of communication partners as well as supports transformation of different message formats.
Communication partners can now communicate through messages without the need to know the message format used by the communication partner or the address by which it can be reached. The message-oriented middleware provides message channels (also referred to as queues). Messages can be written to these queues or read from them. Additionally, the message-oriented middleware contains components that route messages between channels to intended receivers, as well as handle message format transformation.
The messaging framework must have the following capabilities:
- Guaranteeing the delivery of each message or guaranteeing a notification of failed deliveries
- Securing message contents beyond the transport
- Managing state and context data across a service activity
- Transmitting messages efficiently as part of real-time interactions
- Coordinating cross-service transactions
Without these types of extensions in place, the availability, reliability, and reusability of services will impose limitations that can undermine the strategic goals associated with cloud-hosted services.