SA_2014_08(Design-1)

is found repeatedly in practice is a package of design decisions has known properties that permit reuse describes a class of architectures
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Architectural Patterns

These are broadly-scoped solutions to previously encountered problems. An architectural pattern
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Availability Tactics

Availability（可用性）

和系统故障及其后果有关的质量属性

可以理解为计算机在任一时刻正常工作的概率
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Architectural Patterns

These are widely known and include many familiar design approaches:

Layered Pipe-and-filter Client-server

Thin client Thick client Asynchronous Synchronous N-tier client-server

Buschmann, F., R. Meunier, H. Rohnert, P. Sommerlad, and M. Stal. 1996. Pattern-Oriented Software Architecture, Volume 1: A System of Patterns. Wiley.


Styles, patterns, and tactics（战术、策略） represent conceptual tools in the architect’s “tool bag/box” Professional architects always keep their tool bag up to date.
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Patterns and Styles
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Styles to Patterns



Then, the design patterns community arrived. Architectural styles were clearly just patterns, whose scope of design was the whole system – that is, whose scope was the architecture. Now, architectural patterns is the term in use. There are books of architectural patterns, e.g.,



Victorian (multi-story, lots of frilly wood decorations, tall windows, basically square footprint…) Colonial (brick front, pillars or columns, usually symmetrical front…) Ranch (single-story, sprawling, not very decorated…)
Availability Tactics

keep faults from becoming failures or at least bound the effects of the fault and make repair possible. 可用性战术阻止错误发展成为故障或者把错误的影响限制 在一定范围内，从而使修复成为可能。
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Tactics（战术）

An architectural tactic is a fine-grained design approach used to achieve a quality attribute response. Tactics are the “building blocks” of design from which architectural patterns are created.


Peer-to-peer Agent-based systems Service-oriented architectures
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Architectural Patterns

These are widely known and include many familiar design approaches:
5. Designing Architecture
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何时开始设计架构
软件概念
初步的需 求分析 交付最终 ຫໍສະໝຸດ 本架构和系 统核心的 设计
开发一 个版本 交付该 版本 获取客户 反馈
汇总客 户反馈
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A tactic is a design decision（设计决策） that influences the control of a quality attribute response. We call a collection of tactics an architectural strategy.
（检查点回滚）

fault recovery（错误恢复）



fault prevention（错误阻止）

Removal from service, Transactions, Process monitor
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Fault Detection
Creating the Architecture

How does the architect create an architecture? (Multiple choice):
a. By re-using approaches from other architectures b. By inventing new approaches out of thin air c. By magic

Layered Pipe-and-filter Client-server

Thin client Thick client Asynchronous Synchronous N-tier client-server


Peer-to-peer Agent-based systems Service-oriented architectures

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Availability Tactics

fault detection（错误检测）

Ping/echo（命令/响应）, Heartbeat（心跳）, Exceptions Fault recovery consists of preparing for recovery and making the system repair. Voting（表决）, Active redundancy（主动冗余）, Passive redundancy（被动冗余）, Spare（备件）, Shadow operation, State resynchronization（状态再同步）, Checkpoint/rollback
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Tactics


What is it that imparts portability（可移植性） to one design, high performance to another, and integrability（集 成性） to a third? The achievement of these qualities relies on fundamental design decisions.

Ping/echo




One component issues a ping and expects to receive back an echo, within a predefined time, from the component under scrutiny. used within a group of components mutually（互相地） responsible for one task. used by clients to ensure that a server object and the communication path to the server are operating within the expected performance bounds. “Ping/echo” fault detectors can be organized in a hierarchy（层 次）, 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. This uses less communications bandwidth than a remote fault detector that pings all processes.