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A6_DistArchCh2 - Architectures for Distributed Systems...

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Architectures for Distributed Systems Chapter 2
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Definitions Software Architectures – describe the organization and interaction of software components; focuses on logical organization of software (component interaction, etc.) System Architectures - describe the placement of software components on physical machines The realization of an architecture may be centralized (most components located on a single machine), decentralized (most machines have approximately the same functionality), or hybrid (some combination).
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Architectural Styles An architectural style describes a particular way to configure a collection of components and connectors. Component - a module with well-defined interfaces; reusable, replaceable Connector – communication link between modules Architectures suitable for distributed systems: Layered architectures* Object-based architectures* Data-centered architectures Event-based architectures
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Architectural Styles Figure 2-1. The (a) layered architectural style & (b) The object-based architectural style. Object based is less structured component = object connector = RPC or RMI
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Data-Centered Architectures Access and update of data store is the main purpose of the system Processes communicate/exchange info primarily by reading and modifying data in some shared repository (e.g database, distributed file system) Traditional data base (passive): responds to requests Blackboard system (active): clients solve problems collaboratively; system can update clients when information changes.
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Architectural Styles Figure 2-2. (a) The event-based architectural style Communication via event propagation, in dist. systems seen often in Publish/ Subscribe; e.g., register interest in market info; get email updates Decouples sender & receiver; asynchronous communication Event-based arch. supports several communication styles: • Publish-subscribe • Broadcast Point-to-point
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Architectural Styles (5) Figure 2-2. (b) The shared data-space architectural style. Data Centric Architecture; e.g., shared distributed file systems or Web-based distributed systems Combination of data-centered and event based architectures Processes communicate asynchronously
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Distribution Transparency Software architectures are important because they are designed to support distribution transparency. Transparency involves trade-offs Different distributed applications require different solutions/architectures There is no “silver bullet” – no one-size-fits-all system.
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System Architectures for Distributed Systems Centralized : traditional client-server structure Vertical (or hierarchichal) organization of communication and control paths Logical separation of functions into client (requesting process) and server (responder) Decentralized : peer-to-peer Horizontal rather than hierarchical comm. and control Communication paths are less structured; symmetric functionality Hybrid: combine elements of C/S and P2P Edge-server systems Collaborative distributed systems.
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