What is Software Architecture? The exception handler typically executes in the same process that introduced the exception. redundancy . We then consider fault recovery and finally, briefly, fault prevention. 9–18. nowadays, several non-automatic or semi-automatic software architecture evaluation methods have been proposed to evaluate their quality attributes as availability. Realizing and Refining Architectural Tactics: Availability. Software Architecture in Practice (3rd Edition). Availability tactics in software architecture ! Security is responsible for the ability of the system to reduce the likelihood of malicious or accidental actions as well as the possibility of theft or loss of information. In this case one component emits a heartbeat message periodically and another component listens for it. รวมทุกเนื้อหาสาระ ที่เกี่ยวกับ software engineer Availability Tactics - software engineering software engineering when tactics are applied to the software architecture [17]. Tactics for availability: Use replication of the server to cope with downtime. It can also used be used by clients to ensure that a server object and the communication path to the server are operating within the expected performance bounds. The software architecture of a system is the set of structures needed to reason about the system, which comprise software elements, relations among … Process monitor. Benefits. Achieving Qualities. In the fourth week, we will explain how architectural tactics can help you create a software architecture that achieves the predefined requirements. Ping/echo. The following are some fault prevention tactics. Availability Tactics (1) Avoid fault become failures Fault Detection between processes • ping/echo check others • heartbeat message/dead man timer be checked by other within a process • exceptions when a fault is recognized 4 (13) - SOFTWARE ARCHITECTURE Quality Attributes (2) - Sven Arne Andreasson - Computer Science and Engineering It provides an abstraction to manage the system complexity and establish a communication and coordination mechanism among components. One extreme of diversity is that the software for each redundant component is developed by different teams and executes on dissimilar platforms. Tactics that are implemented in existing architectures can have significant impact on the architecture patterns in the system. Processes running on redundant processors each take equivalent input and compute a simple output value that is sent to a voter. A fault (or combination of faults) has the potential to cause a failure. A checkpoint is a recording of a consistent state created either periodically or in response to specific events. Bass, L.; Clements, P.; & Kazman, R. Software Architecture in Practice, Second Edition. 9 September 2008 15-313: Foundations of Software Eng ineering Software Architecture 8 Availability Tactics: Fault Recovery • voting • multiple components produce answer • give client the answer with the most votes • most useful for hardware failures •buggy software will fail in the same way • occurs even if built by different teams! The voting algorithm can be "majority rules" or "preferred component" or some other algorithm. These and all books in the series address critical problems in software engineering for which practical solutions are available. This report describes an updated set of tactics that enable the architect to build availability into a system. The design and subsequent implementation of a high availability architecture can be difficult given the vast range of software, hardware and deployment options. § Patterns package tactics. Achieving Quality Attributes through Tactics. Tactics are fundamental elements of software architecture that an architect employs to meet a system's quality requirements. —Woody Allen Availability refers to a property of software that it is there and ready to carry … - Selection from Software Architecture in Practice, Third Edition [Book] Still others, from the SEI’s CERT Program, describe technologies and practices needed to manage software and network security risk. As you may know, a quote that shaped the way I think about architecture is from Werner Vogels, CTO at Amazon.com. It is usually used for control systems in which the outputs to the voter are straightforward and easy to classify as equivalent or deviant, the computations are cyclic, and all redundant components receive equivalent inputs from sensors. This tactic removes a component of the system from operation to undergo some activities to prevent anticipated failures. Software Architecture in Practice, 3rd Edition ... We call these techniques architectural tactics. In some cases, the monitoring or recovery is automatic and in others it is manual. "Ping/echo" fault detectors can be organized in a hierarchy, in which a lowest-level detector pings the software processes with which it shares a processor, and the higher-level fault detectors ping lower-level ones. The exception handler will usually perform a semantic transformation of the fault into a form that can be processed. Sometimes a system fails in an unusual manner, with a detectably inconsistent state. 11 The software architecture of a computing system is the set of structures needed to reason about the system, which comprise software elements, relations among them and properties of both. Security is a complex quality property due to its … In this case, a single bridge or path failure will not make all of the system's components unavailable. Quality Attributes. Tactics impart portability to one design, high performance to another, and integrability to a third. Video created by EIT Digital for the course "Software Architecture for the Internet of Things". Incremental state upgrades, with periods of service between increments, lead to complicated software. Design Architecture. Recovery reintroduction tactics ! Detection Recovery- reintroduction Recovery- preparation and repair Prevention . These and all books in the series address critical problems in software engineering for which practical solutions are available. The quality attribute requirements specify the responses of the system that, with a bit of luck and a dose of good planning, realize the goals of the business. Architecture patterns describe the high-level structure and behavior of software systems as the solution to multiple system requirements, whereas tactics are design decisions that improve individual quality attribute concerns. Software architecture is the structure or structures of the system, which comprise software elements, the externally visible properties of these elements, and the relationships among them. Availability Tactics, Modifiability Tactics, Performance Tactics, Security Tactics, Testability Tactics, Usability Tactics. Documenting Software Architecture: Views and Beyond, 2nd Ed., Clements et al. Many of the tactics we discuss are available within standard execution environments such as operating systems, application servers, and database management systems. Passive . Other books focus on software and system architecture and product-line development. These and all books in the series address critical problems in software engineering for which practical solutions are available. In a highly available distributed system, the redundancy may be in the communication paths. If it is manual, the system must be designed to support it. A catalog of architectural tactics has now been in use for several years in academia and industry. Architecture serves as a blueprint for a system. Figure 5.13. Some database systems force a switch with storage of every new data item. Variations on this approach include the Simplex approach, which uses the results of a "preferred" component unless they deviate from those of a "trusted" component, to which it defers. The Software Engineering Institute is a federally ... quirements to the domain of architecture has historically been an art more than a science. When a fault occurs, the downtime of systems using this tactic is usually milliseconds since the backup is current and the only time to recover is the switching time. One component (the primary) responds to events and informs the other components (the standbys) of state updates they must make. The current availability architectural tactics catalog [4] provides . Availability tactics are designed to enable a system to endure system faults so that a service being delivered by the system remains compliant with its specification. Architecture in the life cycle. Replication is used on server and database for higher performance and availability. A standby spare computing platform is configured to replace many different failed components. Forcing switchovers periodically-for example, once a day or once a week-increases the availability of the system. The software architecture patterns developed to implement this tactic are: Model-View-Controller Presentation-Abstraction-Control Seeheim Arch/Slinky 29. The downtime for this tactic is usually minutes. What Is Software Architecture? Nevertheless, most architectural strategies have not been developed to … Such tactics are shadow operation, state resynchronization, and rollback. All approaches to maintaining availability involve some type of redundancy, some type of health monitoring to detect a failure, and some type of recovery when a failure is detected. This approach is also used in control systems, often when the inputs come over communication channels or from sensors and have to be switched from the primary to the backup on failure. Then, we'll learn how to combine tactics and patterns. Availability . Still others, from the SEI’s CERT Program, describe technologies and practices needed to manage software and network security risk. An ... CARNEGIE-MELLON UNIV PITTSBURGH PA SOFTWARE ENGINEERING INST, *FAULTS, *SOFTWARE ENGINEERING, FAULT DETECTION, AVAILABILITY, ARCHITECTURE, Collection ... categorization has re-mained stable. In this case, the system should be restored using a previous checkpoint of a consistent state and a log of the transactions that occurred since the snapshot was taken. In the air traffic control system, the secondary decides when to take over from the primary, but in other systems this decision can be done in other components. rework the architecture Tactics: optimize repeated processing reduce contention via replication prioritize processing consolidate related workload distribute processing over time minimize the use of shared resources reuse resources and results partition and parallelize scale up or scale out degrade gracefully use asynchronous processing Synchronization is the responsibility of the primary component, which may use atomic broadcasts to the secondaries to guarantee synchronization. First, we'll look at different types of patterns. PATTERNS AND TACTICS 2.3 Software Architecture The notion of software architecture evolved in the early 90s [11], but the origins date back to the late 60s and early 70s, when the software crisis led to the discipline of software engineering. Availability tactics (2) 6 8.11.2011 . 2010. This report describes how tactics are based on … Not My Problem. Some preparation and repair tactics follow. 2010. Process . Harrison and P. Avgeriou, Incorporating fault tolerance tactics in software architecture patterns, in Proc. Hence, availability tactics have been modeled in the RBML-PI add-in component by Kim [19]. Software Engineering Institute, Carnegie-Mellon University. swe320 Software Architecture. One method for recognizing faults is to encounter an exception, which is raised when one of the fault classes we discussed in Chapter 4 is recognized. Making a checkpoint of the system state to a persistent device periodically and logging all state changes to a persistent device allows for the spare to be set to the appropriate state. Three widely used tactics for recognizing faults are ping/echo, heartbeat, and exceptions. Figure 5.13 shows a summary of the runtime tactics to achieve usability. Some material in these slides is adapted from Software Architecture in Practice, 3rd edition by Bass, Clements and Kazman. The resending of unreceived messages (possibly over different communication paths) continues until the sender marks the recipient as out of service. Shadow State resynchronization Rollback Removal . All redundant components respond to events in parallel. J. Scott Hawker/R. Decision Model for Software Architectural Tactics Selection Based on Quality Attributes Requirements ... by which stakeholders judge their qua Examples of quality attributes by which stakeholders may judge the quality of software systems m ay inc availability, usability, interoperability, configurability, performance, security, modifiability, reliability, portab etc. A previously failed component may be run in "shadow mode" for a short time to make sure that it mimics the behavior of the working components before restoring it to service. Availability experts insist that for any system to be highly available, its parts should be well designed and rigorously tested. Patterns and Tactics Architecture in Agile Projects Designing an Architecture Documenting Software Architectures Architecture and Business Architecture and Software Product Lines The Brave New World 2 . 2013. This message not only acts as a heartbeat but also carries data to be processed. UNIT IV: CREATING AN ARCHITECTURE-II Documenting Software Architectures: Use of Architectural Documentation, Views, Choosing the Relevant Views, Documenting a view, Documentation across … He said: Having worked on large-scale systems for more than a decade, if I could… Further, it involves a set of significant decisions about the organization relat… produce the availability schedule estimate platform availability estimate functional availability assess against the requirements rework the architecture Tactics: select fault-tolerant hardware use high-availability clustering and load balancing log transactions apply software availability solutions select or create fault-tolerant software One example is rebooting a component to prevent memory leaks from causing a failure. More specifically, RBML describes tactics as components and connectors with a specific functionality. When a fault occurs, the system must first ensure that the backup state is sufficiently fresh before resuming services. However, the treatment of architecture to date has largely concentrated on its design and, to a lesser extent, its validation. We first consider fault detection. A failure occurs when the system no longer delivers a service that is consistent with its specification; this failure is observable by the system's users. Heartbeat (dead man timer). Learn vocabulary, terms, and more with flashcards, games, and other study tools. 3. For example, it may be desirable to use a LAN with a number of parallel paths and place each redundant component in a separate path. Software architecture has become a widely accepted conceptual basis for the development of nontrivial software in all application areas and by organizations of all sizes. 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