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2. Architectures CSE5306 Lecture Quiz 2 due 5 PM Tuesday, 9 June 2015

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Architectures Divide & Conquer -- organizes the design of a distributed system. Name the parts and show their interactions. System (multi-server?) architecture precedes (drives) software architecture. Adaptive (tradeoffs) middleware can provide distribution transparency by separating apps from their platforms. Autonomic distributed systems use feedback control loops to monitor their behaviors and adapt.

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Architectural Styles Lets adopt Visios UML 2.0 Object Model Diagram as our (object-based) architectural style. Its components are classes and instances. Its connectors are offspring inherit and cross-family, marital uses. Consider three other styles: Layered architecturesincluding inheritance. Data-centered architecturesprocessors communicating via shared files or web-based data services. Event-based architecturespublish/subscribe systems. Hybrids trading off performance, fault-tolerance, ease of programming, etc. In our chosen object-based architectural style, inheritance also is layered (Fig.2-1, -2, pp.35, 36). Networks have 7 OSI layers: application, down to representation, session, transport, network, data link and physical. Event based systems are loosely or referentially coupled. SQLs shared data spaces are both data-centered and event-based.

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System Architectures A system architecture defines the relationships among users (clients), (server) hardware and both purchased and developed software, from apps through tools to middleware. A system architecture can be centralized, decentralized or a hybrid of the two.

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Centralized Architectures Servers serve up files or databases. Clients make a request and await a reply. If both share the same desktop computer or LAN, they need no phone-like connection. Remote servers (WAN) must first be called. Reliable connection-oriented protocols are slow (e.g., the Internets TCP/IP). Idempotent requests can be repeated; e.g., What is my bank balance? Others cannot; e.g., Transfer $10K to Joe.

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R U O K ? Match the following terms with their example applications below. 1.Object-oriented architectures__ 2.Data-centered architectures __ 3.Layered architectures __ 4.CSE 5306-002s architecture __ 5.Event-based architectures __ a.Networkers 7-level OSI hierarchy and UMLs class inheritance. b.Its components are classes and instances, and its connectors are inherit and uses. c.Yourdons structured data flow diagrams and data structured system design diagrams. d.Loosely coupled publish/subscribe systems. e.Visios UML 2.0 Object Model Diagram

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R U O K ? 6. Which of the following accurately characterize centralized architectures? a.Servers generally serve up files or databases. b.Client-server interactions have a request-reply behavior. c.Clients and servers on the same LAN have connectionless network protocols. d.Clients must connect to distant WAN servers, usually via the Internets via TCP/IP protocol. e.All of the above.

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R U O K ? 7. Which of the following accurately characterize system architecture? a.It defines relationships among clients and servers, hardware and software, whether purchased or developed. b.It can be centralizedoffice LANs printer server. c.It can be decentralizedthe Internet. d.It can be a hybrid of the twoa local database that links to the Internet when it lacks resources. e.All of the above.

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R U O K ? 8. What is the purpose of software architecture? a.It prevents system engineers, who often lack software design skills, from carelessly making software organization decisions. b.It organizes software development tasks before implementation. c.It defines interfaces among software modules and their verification tests. d.It prevents coders, who often lack software design skills, from carelessly making software organization decisions. e.All of the above.

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R U O K ? Match the following terms with their definitions below. 9. Open Systems Interconnection__ 10. Connection-oriented __ 11. Idempotent __ 12. Object-oriented design__ 13. Object model diagram __ a.A request without lingering side effects that can be repeated. b.Calling up a remote server to make a series of requests before hanging up. c.The standard layered architecture of networking. d.Interpreting verbal software specifications as interrelated families of objects (nouns) and operations (verbs). e.Layers of boxes (full of method and object names) that are all interconnected by inheritance or uses arrows.

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Application Layering Three application layers (Fig.2-4, p.39 and above): 1.User interfacedesktop computer GUI client. 2.Processingapplications core functionality. 3.Data levelobject-relational database- or file-specific entry, retrieval and persistent storage, including table descriptions, entry constraints and application-specific metadata.

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Multi-Tiered Architectures A physically 2-tiered client-server application could be as simple as 1) a thin-client dumb terminal and 2) the server handling everything (Fig.2-5a, p.41). Fat clients (Fig2-5e) may give users too much control, resulting in security breeches. In physically 3-tiered architectures, the middle tier is a web server that talks to the client and to application or database servers, as if it were a client (Fig.2-6, p.43).

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R U O K ? Match the following terms with their definitions below. 14. Fat client__ 15. Processing application layer __ 16. Thin client __ 17. User interface application layer __ 18. Data level application layer __ a.A desktop computer GUI client. b.The applications core functionality. c.Object-relational database- or file-specific entry, retrieval and persistent storage, including table descriptions, entry constraints and application-specific metadata. d.Dumb terminal lets server handle everything. e.User terminal handles almost everything, possibly resulting in security breeches.

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R U O K ? 19. In what kind of distributed computer system does a server function as both server and client? a. In physically 3-tiered architectures. b. In bank customer service websites, where the server stands guard between inquiring clients and the banks object-relational transaction database. c. In secure Internet biographical data repositories, where thin clients are unable to access others private data and a highly optimized search engine handles the database. d. All of the above. e. None of the above.

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R U O K ? 20. Which of the following are the data levels responsibilities? a. Making data persist until its next possible use. b. Keeping data consistent across different applications; e.g., ensuring that a debit card user does not withdraw more than his balance. c. Keeping application data independent of organizations and vice versa, so that changes in one do not affect the other (information hiding). d. Accommodating special data representations; e.g., polygons in computer-aided design systems. e. All of the above.

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R U O K ? 21. Which of the following applications would be most suitable for fat clients? a.Consumer banking. b.Algorithm stock traders that are operate autonomously in close proximity to the New York Stock Exchanges transactional database. c.Distributed computer-aided design system used in developing jet fighters. d.Limited access LAN that enables astronomers control of a large telescope. e.Car dealers control of Toyota assembly workers.

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R U O K ? 22. Which of the following applications would be most suitable for thin clients? a.Consumer banking. b.Algorithm stock traders that are operate autonomously in close proximity to the New York Stock Exchanges transactional database. c.Distributed computer-aided design system used in developing jet fighters. d.Limited access LAN that enables astronomers control of a large telescope. e.Car dealers control of Toyota assembly workers.

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R U O K ? 23. Which of the following impact the design of multi- tiered, connection-oriented database applications? a.Reusable data should persist between client requests. b.Clients may use a wide variety of terminal equipment and communication protocols. c.Connections are unreliable; i.e., may drop out and reconnect. d.Users may have criminal intentions. e.All of the above.

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Decentralized Architectures Multi-tiered client-server architectures are vertically distributed among logically different components on different machines. In peer-to-peer systems, a client or servers work is horizontally distributed among logically equivalent parts on different machines, each part sharing the load by working on its own share of the dataset. In interacting with its peers, any individual (called a servent) may behave as a client or as a server. A servent nodes TCP messages to another node typically are routed through many other message- carrier nodes in an overlay network.

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Structured Peer-to-Peer Architectures In structured peer-to-peer architectures, the overlay network is a distributed hash table (DHT). Data items are evenly distributed among nodes that bear their hash codes (e.g., the data items successors in Chord ring of Fig.2-7, p.45). Effective membership management comes from nodes finding shortest communication paths among themselves, so that data lookups can be done in O(log(Node)) steps. Available peers join a Chord ring by generating its hash coded node identifier number and informing its immediate predecessor in the ring. It leaves the ring by giving its data items to its successor and asking its predecessor to replace its name with the name of its successor. The automotive Content Addressable Network (CAN) works similarly in multiple dimensions, two of which appear in Fig. 2-8, p.46. (A new node joins the overworked node on the lower-left, taking a fraction of the formers data items and informing its neighbors of its new data range. A node leaves the space by giving away its data to lightly loaded neighbors.)

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Unstructured Peer-to-Peer Architectures The overlay networks of unstructured peer-to-peer systems (e.g., the Internet) are randomly generated, both the lists of neighbors and the data that they oversee. To locate a needed data item, node A broadcasts (i.e., pushes) its request throughout the network. Node A adds the node that responds (node B) to its partial view (i.e., routing table) of nodes. When node A responds to (i.e., pulls) another nodes (node C) broadcast, it also adds the broadcaster to its partial view. To join the network, an available peer asks the most frequent contacts on its partial view to share their data items. When a node leaves the network (and fails to respond to requests), its requesters delete it from their partial views. Very popular nodes are said to have high indegree. If overloaded by requests, it can lower its popularity by simply ignore some.

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R U O K ? Match the following terms with the definitions below. 24. Overlay network__ 25. Horizontal distribution__ 26. Peer-to-peer system__ 27. Servent__ 28. Vertical distribution__ a.Separating clients from servers in multiple tiers of logically different components on different machines. b.Spreading a client or servers excessive workload among his peers (i.e., logically equivalent parts) on different machines. c.Distributing a client or servers extra work among its peers; i.e., logically equivalent parts on different machines. d.An processor that can assume the role of a client or server to assist an overloaded peer. e.A distributed hash table (DHT) that lists node owners of data items in a peer-to- peer system.

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R U O K ? 29. Which of the following characterizes a Chord ring of peer-to-peer nodes? a.Data items are evenly distributed among nodes that bear their hash codes. b.Nodes are logically organized into a ring, such that a data item with key i belongs to the nearest successor node with key k > i. c.An available peer joins by generating its own hash-coded node identifier number and introducing itself to its immediate predecessor. d.A peer leaves the ring by giving its data items to its successor and asking its predecessor to replace its name with the name of its successor. e.All of the above.

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R U O K ? 30. Which of the following characterizes a Content Addressable Network (CAN) of peer-to-peer nodes? a.It is like a Chord, but with multiple Cartesian coordinate dimensions. b.An available node joins the network by accepting half of the data items of an overworked existing node, and informing all nearest neighbors of its and its benefactors new ranges of data. c.A peer leaves the network by giving away its data to its most lightly loaded neighbors. d.All of the above. e.None of the above.

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R U O K ? 31. Which of the following characterizes an unstructured system of peer-to-peer nodes? a.Like the Internet, its overlay networks (i.e., the lists of neighbors and the data that they oversee) are randomly generated. b. To locate a needed data item, a node broadcasts (i.e., pushes) its request throughout the network. c. The broadcasting node adds the responder to its partial view of nodes. And when a node responds to (i.e., pulls) another nodes broadcast, it adds the broadcaster to its partial view. d. To join the network, an available peer asks the most frequent contact on its partial view to share its data items. And when a node leaves the network (and fails to respond to requests), its requesters delete it from their partial views. e. All of the above.

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R U O K ? Match the following terms with their definitions below 32. CAN__ 33. DHT__ 34. membership management__ 35. partial view __ 36. Indegree __ a.Nodes finding shortest communication paths among themselves, so that data lookups can be completed in O(log(Node)) steps. b.The number of other partial views that that contain this nodes number; i.e., a measure of its popularity. c.The automotive Content Addressable Network that distributes nodes over a multi-dimensional Cartesian coordinate space. d.The distributed hash table that serves as structured peer-to-peer systems overlay network. e.A routing table that lists nodes and the data items they manage.

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Topology Management of Overlay Networks Structured P2P architectures have better membership management; unstructured P2Ps are faster and distribute nodes workloads more evenly, but a hybrid can beat both. Let the unstructured one work independently below and the structured one optimize its results in a higher architectural layer (Fig. 2-10, p.49). Optimizing criteria (ranking functions) encourage commerce with physically or semantically nearest neighbors (Fig. 2-11, p.50). Very efficient search algorithms use semantic overlay networks that structured P2P systems imposed upon unstructured P2P systems.

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Super-Peers When too many nodes slow down an unstructured P2P system, its supervising structured P2P system can ask similar nodes to elect a representative superpeer (Fig. 2-12, p.51). Then a node queries a few superpeers, instead of flooding the whole network with its broadcast. Superpeers maintain an index of its subordinates data items and gather popular (distant) web pages to rapidly fulfill local searches (content delivery network). Superpeers should be long-lived and highly available. Super-superpeers also can be hierarchically organized. A client may adopt a favorite superpeer to serve collected files. As nodes join and leave a network, periodic reelections may be needed.

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Hybrid Architectures Yet another optimized hybrid results from marrying client-server and decentralized architectures. An edge-server enhances enterprise networks Internet access. Collaborative distributed systems encourage servers or even end users to help others and to call upon others for help.

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Edge-Server Systems Internet service providers like AT&T connect a great many users homes to the Internet (Fig 2- 13, p.52). Edge servers serve wide-band Internet content to whole enterprise networks full of always- connected users (e.g., AT&T itself). AT&Ts dedicated edge server optimizes both content and the distribution of applications. AT&Ts edge server can call upon other local edge servers to broker distant web pages, etc.

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Collaborative Distributed Systems Instead of a dozen clients requesting a big file from a distant server, each client should request a chunk and share it with the others. BitTorrent (Fig.2-14, p.53) encourages such behavior by serving chunks only to those who promise to share. A few websites have.torrent files that identify tracker servers, which maintain lists of active nodes having chunks of a desired file. An active node is one that currently is downloading another file. To continue downloading its desired file, it also must serve a file that it already has to others. If it is giving less than it is is getting, its provider reduces its data rate. Successful nodes actively seek trading relationships.

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Collaborative Distributed Systems (Continued) The Globule collaborative content distribution network consists of end users, who voluntarily replicate distant web pages. Each user has a manager, an analyzer and a broker. The broker may refer requests to other servers, who can serve some web pages better. The broker may be replicatedredundancy enhances reliability.

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R U O K ? Match the following terms with their definitions below. 37. BitTorrent __ 38. Superpeer __ 39. Edge server __ 40. Globule__ 41. Ranking functions __ a.Optimizing criteria that encourage commerce with physically or semantically nearest neighbors. b.Many nodes elected representative, which makes broadcasting requests unnecessary. c.A whole enterprise networks internet service provider. d.A system that promotes collaborations among file servers. e.A system that makes users into web page brokers.

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Architectures v. Middleware Middleware is the singular architectural layer between applications and distributed platforms (Fig.1-1, p.3). It provides distribution transparency by translating between varied application languages L2 and hardware languages L1. A middleware product (e.g., object-oriented CORBA) may become bloated, if it tries to offer interaction patterns for everyone.

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Interceptors An object calls all methods the same way, whether they are local or remote. When a method is remote, the objects local interface must intercept the call. The middlewares request-level interceptor transforms it into a generic object invocation. The middlewares message-level interceptor sends it as a message to the local operating systems LAN transport layer, possibly breaking up any transmitted files into blocks for reassembly by the remote middleware. Un-intercepted local calls simply pass through the middleware to the local operating system.

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General Approaches to Adaptive Software Distributed applications runtime environments are continually changing. Middleware presents a stable environment, handling all cell phone mobility, network quality-of-service dips, hardware failures and battery drainage problems. These adaptations are categorized as: Separation of concernsaspect-oriented software development weaves security and fault tolerance into the middlewares application services. Computational reflectionsmiddleware continually inspects and adjusts its own runtime performance. Component-based designmiddleware reconfigures itself at runtime with late binding to modules that are loaded or unloaded at will.

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Discussion Services that applications demand from middleware (specialization) conflict with needs for middlewares distribution transparency (generality). Flexibility leads to complexity. External simplicity arises from selectively configuring components and application independence. Distributed systems must not fail, so they must adapt to changing environments by automatically replacing and upgrading components at runtime.

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R U O K ? 42. What might cause a middleware to become bloated? a.Applications demands for middleware services (specialization) competing with middlewares distribution transparency (generality). b.Enabling users to selectively configure components as needed. c.Application independence. d.Flexibility, which leads to complexity. e.Both a and d above.

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R U O K ? Arrange the following in their proper sequence. 43. __ (first step)46. __ 44. __47. __ (last step) 45. __ a. Un-intercepted local calls simply pass through the middleware to the local operating system. b. An object calls every method the same way, whether local or remote. c. If the method is remote, the objects local interface intercepts the call. d. The middlewares message-level interceptor sends the call as a message to the local operating systems LAN transport layer, possibly breaking up any transmitted files into blocks for reassembly by a remote middleware. e. The middlewares request-level interceptor transforms the call into a generic object invocation.

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R U O K ? Match the following terms with their definitions below. 48. CORBA__ 49. Interceptor __ 50. Middleware__ 51. Request-level interceptor __ 52. Message-level interceptor __ a.A middleware object that redirects RPCs to the LAN. b.Transforms calls into messages and transfers file blocks. c.A popular object-oriented middleware. d.Transforms method calls into a generic object invocations. e.Interprets language L0 below into language L1 above and vice versa, while presenting a stable client environment.

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R U O K ? 53. How does middleware adapt its distributed system to environmental changes? a.Separation of concernsaspect-oriented software development weaves security and fault tolerance into the middlewares application services. b.Computational reflectionsmiddleware continually inspects and adjusts its own runtime performance. c.Component-based designmiddleware reconfigures itself at runtime with late binding to modules that are loaded or unloaded at will. d.All of the above. e.None of the above.

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R U O K ? 54. How is middleware similar to and different from other architectures? a.Middleware is a single layer. b.Middleware developers adopt a variety of organization schemes, with varying success. c.Middleware tends to become bloated as developers strive to organize it to serve every application. d.All of the above. e.None of the above.

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Self-Management in Distributed Systems To automatically adapt to changing environments, we must organize components for monitoring and adjustments, while deciding where their processes must be executed. Autonomic computing starts with a high-level feedback control system that self-manages, self-heals, self-configures and self-optimizes.

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The Feedback Control Model Self-managing systems adapt to their changing environments by means of one or more feedback control loops. The Initial Configuration includes the customers performance requirements and potential customers desirements. Uncontrollable Parameters include ongoing environment changes and random perturbations. Analysis estimates the distributed systems current performance metrics and continually tweaks it, feeding configuration Corrections into the systems input. Estimates implies that some performance parameters cannot be measured directly; e.g., a remote nodes latency. Corrections may include reprioritizing schedules, choosing a higher quality-of-service, caching heavily used data or replicating. Every corrections effects also are carefully evaluated. Like any architecture, the feedback loop is a logical organization; its distributed physical implementation may look quite different.

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Systems Monitoring with Astrolabe An Astrolabe zone automatically summarizes performance attributes from all of its hosts robotic agents; e.g., files, resources. User programmable aggregation functions use SQL-like commands to aggregate zone data: SELECT AVG(procs) AS avg_procs FROM hostinfo Gossiping occasionally provides supplementary distant data. Astrolabe passes its performance summaries on to external tools for analyses and corrective actions.

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R U O K ? 55. Which of the following accurately describe the self-management of distributed systems? a.Broken systems healing themselves. b.Systems reconfiguring at runtime, as their environments change. c.Organizing components for monitoring and adjustments in changing environments. d.Continually optimizing performance under stress. e.All of the above.

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R U O K ? 56. Which of the following accurately describe the feedback control model? a.Its initial configuration includes the customers performance requirements, as well as potential customers desirements. b.Its uncontrollable parameters include ongoing environment changes and random perturbations. c.The analysis block in its feedback branch estimates the distributed systems current performance metrics and continually tweaks it, feeding configuration corrections into the systems input. d.Like any architecture, the feedback loop is a logical organization; its distributed physical implementation may look quite different. e.All of the above.

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R U O K ? 57. How can the feedback control model correct distributed system failures? a.It can reprioritize schedules. b.It can choose a higher network quality-of- service. c.It can cache heavily used data. d.It can replicate heavily used data. e.All of the above.

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R U O K ? 58. Which of the following accurately describe system monitoring with Astrolabe? a.An Astrolabe zone automatically summarizes performance attributes from all of its hosts robotic agents; e.g., files, resources. b.User programmable aggregation functions use SQL- like commands to summarize zone data. c.Gossiping occasionally provides supplementary data from nodes outside the zone. d.Analysis and corrective actions are outside Astrolabes scope. e.All of the above.

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R U O K ? 59. What does this SQL-like preprogrammed command direct Astrolabe to mean: SELECT AVG(procs) AS avg_procs FROM hostinfo a.Repair the failed component, which can be identified by its deficient average procedural performance. b.Average all procedure attributes in the zones host information file and store them in the avg_procs object. c.Analyze the performance of all components, and display their mean performance. d.Replace a below-average component. e.None of the above.

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Differentiating Replication Strategies in Globule A Globule collaborative content distribution networks end-user servers replicate origin server web pages (p.54). Seeing many Texas customers reading her web catalog, a consumer electronics exporter in Tokyo (automatically) decides to replicate popular catalog pages on a Texas edge server to improve those customers web performance. 30-50 policies for updating these replicates may be explored, with weighted values of trans-Pacific bandwidth, customer request latencies, number of viewable stale copies, etc. Poor (high cost) policies arise from taking too few measurements or taking too long to gather enough. The minimal cost is somewhere in between (see above).

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Automatic Component Repair Management in Jade In servers with component-based designs, Jade continually tests all components; it replaces failed components with new ones; and it restores all bindings with other components, as well as the servers state just prior to failure. A component has two types of interfaces: Its server interface calls methods in that component. Its client interface calls other (possibly remote) components. In Jades repair management domain, there may be many servers, each with its own node manager (possibly replicated for reliability), which adds and removes nodes (servers) from the domain. Every component offers a variety of self-tests; e.g., exception states, resource usage problems, hardware failures. A preprogrammed repair procedure begins after each failure: 1.Node manager terminates all bindings with the faulty node (server). 2.It starts a new node and adds it to the domain. 3.It configures the new node like the crashed one. 4.It reestablishes all previously terminated bindings.

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Summary Software architecture differs from system design in the following ways. Software architecture is concerned about the logical organization of the software: 1) how components interact, 2) how they are structured and 3) how they can be made independent. System design considers where the distributed systems components are physically placed among the various machines. A model-based system design demonstrates system performance (the customers requirements), while providing a high-level (MATLAB) description of the target code that software developers understand. The software architecture renders a system design on a UML 2.0 object model diagram of classes and dependencies. There are other popular architectural styles for organizing the interactions among a distributed systems components. Layering. Object orientation. Event orientation. Data space orientation. Distributed architectures differ from centralized client-server systems. Distributed architectures tend to be peer-to-peer systems. The peer-to-peer system is organized into an overlay network. The overlay network is a process list of those peers, with whom it can communicate. Overlay networks can be structured (deterministic), unstructured (random) or an optimized hybrid of both.

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R U O K ? 60. Which of the following exemplify Globules replication performance? a.An exporter in Japan asks a Texas edge server to replicate web-based catalog pages for loyal Texas customers convenience. b.Many tens of policies may be considered in deciding how often to update each replicated web page. c.Excessively costly policies arise from taking too few measurements or taking too long to gather enough. d.All of the above. e.None of the above.

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R U O K ? 61. Which of the following accurately describe Jades component repair services? a.They work only on servers with component- based designs. b.Jade continually tests all components. c.Jade replaces failed components with new ones. d.Jade restores all prior bindings with other components, as well as the servers state just prior to failure. e.All of the above.

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R U O K ? 62. How is software architecture different from system design? a.Software architecture is concerned about the logical organization of the software: 1) how components interact, 2) how they are structured and 3) how they can be made independent. b.System design considers where the distributed systems components are physically placed among the various machines. c.Your model-based system design clearly demonstrates desired target system performance to the customer, while providing all software developers a high-level (MATLAB) description of the target code. d.As software architect and designer, you interpret the system design as 1) a UML 2.0 object model diagram of classes and dependencies and 2) sequence diagram of methods messages. e.All of the above.

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R U O K ? 63. Which of the following are popular architectural styles for organizing the interactions among a distributed systems components? a.Layering. b.Object orientation. c.Event orientation. d.Data space orientation. e.All of the above.

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R U O K ? 64. How do distributed architectures differ from centralized client-server systems? a.Distributed architectures tend to be peer-to- peer systems. b.The peer-to-peer system is organized into an overlay network. c.The overlay network contains every process list of peers, with whom it can communicate. d.Overlay networks can be structured (deterministic), unstructured (random) or an optimized hybrid of both. e.All of the above.