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Architectures of Distributed Systems.pdf

Architectures of Distributed Systems

Engineering◦
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ARCHITECTURES for Distributed Systems
Architectural Styles • Important styles of architecture for distributed systems Layered architectures Object-based architectures Data-centered architectures Event-based architectures
Layered Architectural Style • The layered architecture divides the system into distinct layers, each with a specific function. • This style promotes modularity, simplifies development, and enhances maintainability. • A request goes from the top down, and the response goes from the bottom up. • The advantage is that it keeps things orderly and modifies each layer independently without affecting the rest of the system.
Object-based Architectural Style • Each component is an object, and all the objects can interact through an interface (or connector). • Communication between objects happens through method invocations, often called remote procedure calls (RPC) • Popular in client-server systems
Event-based Architectural Style • The entire communication is through events. When an event occurs, the system gets the notification • Sometimes, these events are data, and at other times they are URLs to resources. • The receiver can process what information they receive and act accordingly. • Advantages: • the components are loosely coupled. It means that it’s easy to add, remove, and modify them. • allowing heterogeneous components to communicate with the bus, regardless of their communication protocols.
Shared Data-space Architectural Style • Works on a central data repository, either active or passive. Sometimes, this central repository can be just a simple database. • All communication between objects happens through a data storage system in a data-centered system. It supports its stores’ components with a persistent storage space such as an SQL database, and the system stores all the nodes in this data storage. • Decoupled in space and time • Post items to shared space; consumers pick up at a later time
Centralized Architectures • General interaction between a client and a server. • Application layering • User-interface level • Processing level • Data level
Search Engine Example • The simplified organization of an Internet search engine into three different layers.
Multi-tiered Architectures • The simplest organization is to have only two types of machines: • A client machine containing only the programs implementing (part of) the user-interface level • A server machine containing the rest, • the programs implementing the processing and data level
Multitiered Architectures • From browser-based to phone-based to desktop apps
Three-tier Web Applications • Server itself uses a “client-server” architecture • 3 tiers: HTTP, J2EE and database – Very common in most web-based applications
Structured Peer-to-Peer Architectures • Peer-to-peer systems: • Removes distinction between a client and a server • Overlay network of nodes • Chord: structured peer-to-peer system • Use a distributed hash table to locate objects • Data item with key k -> smallest node with id >= k
Structured Peer-to-Peer Architectures • The mapping of data items onto nodes in Content addressable network (CAN) • d-dimensional coordinate system • Partitioned among all nodes in the system
Structured Peer-to-Peer Architectures • Every data item maps to a point • Join: pick a random point, split with node for that point • Leave: harder, since a merge may not give symmetric partitions
Unstructured Peer-to-Peer Architectures •Topology based on randomized algorithms • Each node pick a random set of nodes and becomes their neighbors • Choice of degree impacts network dynamics
Unstructured Peer-to-Peer Architectures The steps take by the passive thread
Superpeers • A hierarchical organization of nodes into a superpeer network. • Some nodes become “distinguished” • Take on more responsibilities (need to have or be willing to donate more resources) • Example: Skype super-peer
Edge-Server Systems • Viewing the Internet as consisting of a collection of edge servers. • Edge servers: from client-server to client-proxy-server • Content distribution networks: proxies cache web content near the edge
Collaborative Distributed Systems • BitTorrent: Collaborative P2P downloads • Download chunks of a file from multiple peers • Reassemble file after downloading • Use a global directory (web-site) and download a .torrent • torrent contains info about the file • Tracker: server that maintains active nodes that have requested chunks • Force altruism: » If P sees Q downloads more than uploads, reduce rate of sending to Q
Collaborative Distributed Systems • Components of Globule collaborative content distribution network: • A component that can redirect client requests to other servers. • A component for analyzing access patterns. • A component for managing the replication of Web pages.
Topology Management of Overlay Networks • A two-layered approach for constructing and maintaining specific overlay topologies using techniques from unstructured peer-to-peer systems.
Topology Management of Overlay Networks • Generating a specific overlay network using a two-layered unstructured peer-to-peer system
Interceptors • Using interceptors to handle remote-object invocations.
General Approaches to Adaptive Software • Three basic approaches to adaptive software: • Separation of concerns • Computational reflection • Component-based design
The Feedback Control Model • The logical organization of a feedback control system.
Example: Systems Monitoring with Astrolabe • Data collection and information aggregation in Astrolabe.
Example: Differentiating Replication Strategies in Globule • The edge-server model assumed by Globule.
Example: Differentiating Replication Strategies in Globule • The dependency between prediction accuracy and trace length.
Example: Automatic Component Repair Management in Jade • Steps required in a repair procedure: • Terminate every binding between a component on a nonfaulty node, and a component on the node that just failed. • Request the node manager to start and add a new node to the domain. • Configure the new node with exactly the same components as those on the crashed node. • Re-establish all the bindings that were previously terminated.