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Distributed Architecture

Distributed Architecture. Objective. Introduce Distributed Arch. Client/Server Multi-tier Broker Service Oriented Discuss Pros and Cons. Introduction. Distributed System Computers connected through network Components are distributed Two important issues:

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Distributed Architecture

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  1. Distributed Architecture

  2. Objective • Introduce Distributed Arch. • Client/Server • Multi-tier • Broker • Service Oriented • Discuss Pros and Cons

  3. Introduction • Distributed System • Computers connected through network • Components are distributed • Two important issues: • Topology: the way components connected • Mode: the way they communicate with each other • Many models available • Each has pros and cons

  4. Client/Server • The most commonly distributed system architecture • It has two communicating processes • Running on different processors • So, it is decomposed into two major subsystems: • Client • Server • Server process receives the request, carries it out, and sends a reply to the client

  5. Client/Server • Two tier: client and server Back-end tier focuses on business logic and database management Front-end tier focuses on the user interaction

  6. Client/Server Summary • Advantages: • Responsibility separation such as user interface presentation and business logic processing • Reusability of server components • Disadvantages: • Lack of heterogeneous infrastructure to deal with the requirement changes • Security complications • Server availability and reliability • Testability and scalability

  7. Multi-tier • At least 3 tiers • Front-end tier - User interface presentation tier • Middle-end tier - Business logic tier • Manages business logic and execution • Back-end tier - DB management tier • Handles database

  8. Multi-tier

  9. Multi-tier • Advantages of multi-tier over two-tier architecture. • Enhanced reusability and scalability by adding the middle tier • Middle layer is easy to change • Have portable and nonproprietary design and implementation • Middle layer can provide multi-threading support • Reduces traffic on the network • Cons • Difficulty in testing due to lack of testing tools • Adding multiple servers in the system makes the server reliability and availability even more critical

  10. The Broker architectural pattern • Transparently distribute aspects of the software system to different nodes • An object can call methods of another object without knowing that this object is remotely located. • CORBA is a well-known open standard that allows you to build this kind of architecture.

  11. Example of a Broker system

  12. Broker Style • Typical middleware arch. from mid 1990’s • Key Idea: • Service provider register services through broker • Clients discover services through broker • Clients submit requests to broker • Broker massages requests from clients and relay results from service provider • Typical examples: • CORBA, RPC, and RMI

  13. Broker Architecture • Sub-components include • Broker – provide service registration • Stub (client-side proxy) – provide “stub” version of remote services, responsible for massaging messages • Skeleton (server-side proxy) – encapsulates lower network details, dispatch requests to local service objects • Bridges (optional) – for interaction with brokers • Network – for interaction with brokers

  14. Broker Architecture • Broker • It coordinates communications, passing on request and returning replies • It stores all servers’ • registration information, their functionalities and location information • It provides APIs for clients to request, servers to respond, registering or unregistering server components, transferring messages, and locating servers.

  15. Broker Architecture • Stub (Client-side proxy) • Mediates between the client and the broker and providing additional transparency between them. • To the client, a remote object appears like a local one. • The proxy hides inter-process communication at protocol level, marshals the parameter values, and unmarshals results from the server. • The stud is generated at compilation time and deployed at client side to be used as a proxy for client

  16. Broker Architecture • Skeleton (server-side proxy) • It is also generated by service interface compilation and deployed at server side • Encapsulates low-level system specific networking functions like client proxy and provides high level APIs to mediate between the server and the broker • It receives and unpacks the requests, unmarshals the arguments, and calls the appropriate service. • When receives the result back from the server, it also marshals results before sending it back to the client.

  17. Broker Architecture • Bridges • Optional component • Hide implementation details when two brokers interoperates • Can translate requests and parameters from one format to another

  18. Broker Architecture • Network • Connects components using designated protocol standards such as • TCP/IP • OIIP • SOAP • The request carries data in a message document or method invocation format.

  19. Broker Architecture • Example – Broker Model Service 1 2 1 Request Broker 1 3 Service 2 5 Response 4 Service 3 Broker 2

  20. Broker Architecture • Connected Broker with client-server proxy Client Proxy Broker 1 Server Proxy Bridges Server Proxy Broker 2 Client Proxy Broker 3 Client Proxy Server Proxy

  21. Summary – Broker Style • Advantages • Server component implementation and location transparency, • Changeability and extensibility, • Feasibility of run time changes of server components (add or remove server components) • Disadvantages: • Inefficiency due to the overhead of proxies • Low fault tolerance • Difficulty testing

  22. Broker Example – CORBA • CORBA – Common Object Request Broker Architecture

  23. Static Remote Invocation in CORBA • Steps to make things work • service published using IDL (Interface Definition Language) • service implemented by extending Servant class and registered by extending Service class • client implemented by locating name service and invoke service

  24. Dynamic CORBA Invocation • Dynamic? • The invoker does not have to know all details of service provider, e.g., parameter format • Information is disclosed by broker at run time • Relies on 3 components • CORBA Interface Repository (IFR) • Dynamic Invocation Interface (DII) • Dynamic Skeleton Interface (DSI)

  25. Message Broker Architecture • Message: formatted information e.g., XML

  26. Message Broker Architecture

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