Software Architecture - Principles Patterns and Practices - OSI Days Workshop - 2016

transcript

Ganesh Samarthyam ganesh@codeops.tech

www.codeops.tech

Software Architecture: Principles, Patterns, and Practices

Why do you want to become an architect?

What skills are required for an

architect?

Who is an architect?

What essential knowledge is required

for an architect?

What is software architecture?

How to evolve an architecture?

What is the software architecture

development process?

What factors influences software architecture?

Generalist

Specialist

Source: Software Architecture for Developers, Simon Brown, LeanPub, 2014

What is software architecture?

“The software architecture of a program or computing system is the structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the

relationships among them”

Source:So)wareArchitectureinPrac2ce(2ndedi2on),Bass,Clements,Kazman;Addison-Wesley2003:

“Architecture is a set of principal design decisions about a software system”

Source: R. N. Taylor, N. Medvidovic, and E. M. Dashofy. 2009. Software Architecture: Foundations, Theory, and Practice. Wiley Publishing.

“The architecture of a deployed software is

determined by those aspects that are hardest to change”

Source: R. N. Taylor, N. Medvidovic, and E. M. Dashofy. 2009. Software Architecture: Foundations, Theory, and Practice. Wiley Publishing.

Architecture represents the significant design decisions that shape a

system, where significant is measured by cost of change.

- Grady Booch (2006)

Constraints

TechnologyCross-cutting concerns

Others (e.g.: overall

structure)

Dimensions of ADs

Cross-cutting concerns

Error/Exception handling

ConcurrencyPersistence

Event handling

Interaction and presentation

Source: SWEBOK v3

Architecture?**

Network*architecture*

Solu2on*architecture*

Applica2on*architecture*

Pla6orm*architecture*

Data*architecture*

Hardware*architecture*

Web*architecture**

Source: Software Architecture for Developers, Simon Brown, LeanPub, 2014

Architecture/design determines qualities

Understandability Changeability Extensibility

Reusability Testability Reliability

Arch/Design

impactsimpacts

impacts

Architecture principles and styles

Architectural principles: Axis, symmetry, rhythm, datum, hierarchy, transformation

Dravidian styleRenaissance style

Mughal style

Post-modern style

What architectural style is this?

Image source: http://ashokbasnet.com.np/wp-content/uploads/2011/03/wx_thumb-5B1-5D.jpg

Example: Abstracting for portability using layering

•  Helps'abstract'pla-orm0specific'details'abstrac4ng'hardware'specific'aspects''

Hardware'Abstrac4on'Layer'(HAL)'

•  Abstracts'OS'specific'func4onality'and'provides'a'generic'interface'to'underlying'OS'

Opera4ng'System'

Abstrac4on'Layer'(OSAL)'

•  Hides'database'specific'aspects'by'providing'a'generic'interface''

Database'Abstrac4on'Layer'(DAL)'

Layering style: Benefits

+ Reuse of layers

+ Support for standardization

+ Dependencies are kept local

+ Exchangeability

Frank Buschmann, Regine Meunier, Hans Rohnert, Peter Sommerlad, and Michael Stal. 1996. Pattern-Oriented Software Architecture: A System of Patterns. John Wiley & Sons, Inc., NY, USA.

Layering style: Liabilities

- Cascades of changing behavior

- Lower efficiency

- Unnecessary work

- Difficulty in establishing the correct granularity of layers

What architectural style is this?

$ cat limerick.txt There was a young lady of Niger Who smiled as she rode on a tiger. They returned from the ride With the lady inside And a smile on the face of the tiger.

$ cat limerick.txt | tr -cs "[:alpha:]" "\n" | awk '{print length(), $0}' | sort | uniq1 a 2 as 2 of 2 on 3 And 3 Who 3 she 3 the 3 was 4 They 4 With 4 face 4 from 4 lady 4 ride 4 rode 5 Niger 5 There 5 smile 5 tiger 5 young 6 inside 6 smiled 8 returned

List<String> lines = Files.readAllLines(Paths.get("./limerick.txt"), Charset.defaultCharset());

Map<Integer, List<String>> wordGroups = lines.stream() .map(line -> line.replaceAll("\\W", "\n").split("\n")) .flatMap(Arrays::stream) .sorted() .distinct() .collect(Collectors.groupingBy(String::length));

wordGroups.forEach( (count, words) -> { words.forEach(word -> System.out.printf("%d %s %n", count, word)); });

1 a 2 as 2 of 2 on 3 And 3 Who 3 she 3 the 3 was 4 They 4 With 4 face 4 from 4 lady 4 ride 4 rode 5 Niger 5 There 5 smile 5 tiger 5 young 6 inside 6 smiled 8 returned

Real-world pipes-and-filters

sediment pre-carbon ultra-filter post-

carbonFiltered water

Pipe-and-filter: Benefits

+ Flexibility by filter exchange

+ Flexibility by recombination

+ Reuse of filter components

+ Rapid prototyping of pipelines

Pipe-and-filter: Liabilities

- Sharing state information is expensive or inflexible

- Efficiency gain by parallel processing is often an illusion

- Data transformation overhead

- Difficult to handle errors

POSA - before and after

Layered

Pipe-and-Filter

Broker

Client-Server

Peer-to-Peer

Blackboard

What is the architecture

style followed by World Wide Web (WWW)?

SOA (Service Oriented Architecture)

Lambda Style

Microservices

REST (Representational State Transfer)

Map-Reduce

CQRS (Command-Query Responsibility Segregation )

Software Containers

Event Sourcing

Command Query Responsibility Segregation (CQRS) pattern

source: https://msdn.microsoft.com/en-us/library/jj591573.da82141c6f9950d64c1263fa4da825ec(l=en-us).png

Event Sourcing pattern

source: https://msdn.microsoft.com/en-us/library/dn589792.aspx

Map-Reduce patternInput

Sara Booch Thayer Merlin Sara Ralph Merlin Tim Sara

Christian Ralph

Cormen …

Computer Cluster

Sara, 1 Ralph, 1 Merlin, 1 Tim, 1

Sara, 1 Booch, 1 Thayer, 1 Merlin, 1

Sara, 1 Christian, 1

Ralph, 1 Cormen, 1

reduce

Sara, 3 Booch, 1 Thayer,1 Merlin, 2 Ralph, 2 Tim, 1

Christian, 1 Cormen, 1

Output Sara, 1 Sara, 1 Sara, 1

Booch, 1 Thayer, 1

Merlin, 1 Merlin, 1 Ralph, 1 Ralph, 1 Tim, 1

Christian, 1 Cormen, 1

What style is this?

Batch layer

Serving layerSpeed layer

Lambda style

source: https://spark-summit.org/2014/wp-content/uploads/2014/07/Lambda-Architecture-Jim-Scott..pdf

Microservices is an architectural style

Complex application = composed of tiny services

Communicate over REST API

HTTP GET

HTTP PUT

HTTP POST

HTTP DELETE

Underlying philosophy

“do one thing and do it well”

Monolithic

Microservices

Conway’s law“Any organization that designs a system… will inevitably produce

a design whose structure is a copy of the organization's communication structure”

Conway’s lawTeam 1

Team 2Team 3

Team 4

Conway’s law

Team 1 Team 2

Team 3

Team 4

Monolithic to microservices

Service = manageable by “two pizza” team

Amazon’s rules for teams• All teams will henceforth expose their data and functionality

through service interfaces. • Teams must communicate with each other through these

interfaces. • There will be no other form of inter-service/team communication

allowed: no direct linking, no direct reads of another team’s datastore, no shared memory model, no backdoors whatsoever. • The only communication allowed is via service interface calls

over the network. • It doesn’t matter what technology they [other services] use. • All service interfaces, without exception, must be designed from

the ground up to be externalizable. • That is to say, the team must plan and design to be able to

expose the interface to developers in the outside world.

Service = a team can DURS (Deploy, Update, Replace, Scale)

Microservices = Damn U R Sexy

Amazon case study

2-tier architecture SOA Microservices

Triggering microservices

Source: DevOps: A Software Architect's Perspective, Len Bass, Ingo Weber, Liming Zhu, Addison-Wesley Professional, 2015

Separate data stores

A process for architecting using scenarios

Source: http://msdn.microsoft.com/en-us/library/ee658084.aspx

Strategies and tacticsA tactic is a design decision that influences the control of a quality

attribute response

A collection of tactics is known as “strategies”

Source: Len Bass, Paul Clements, and Rick Kazman. 2003. Software Architecture in Practice (2 ed.). Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA.

Example: Security tactics

Security

Resisting Attacks

Detecting Attacks

Recovering From attack

!  Authenticate users !  Authorize users !  Maintain data

confidentiality !  Maintain integrity !  Limit exposure !  Limit access

Restoration Identification

Stimulus:

Attack Response:

System detects, resists, or recovers from attacks

See “Availability“ Audit Trail

Intrusion Detection

Exercise: Tactics for achieving qualities

Availability The property of software that it there and ready to carry out its task when you need it to be

Testability The ease with which software can be made to demonstrate its faults through (typically execution-based) testing

SecurityMeasure of the system’s ability to protect data and

information from unauthorised access while still providing access to people and systems that are authorized

Performance The software’s ability to meet timing requirements

Modifiability The ease with which the software can be modified (with minimal risk and cost)

Tactics for availabilityUse$fault$detec,on$tac,cs$such$as$

ping/echo,$heartbeat,$,me$stamping,$sanity$checking,$

condi,on$monitoring,$and$self:test$

Use$fault$recovery$tac,cs$such$as$rollback$(to$a$previous$known$

good$state),$providing$“spares”$for$redundancy,$retry$the$opera,on,$ignoring$faulty$behavior,$and$

degrade$(gracefully$reduce$system$func,onality)$

Use$fault$preven,on$tac,cs$such$as$removal$from$service$

(temporarily$remove$the$faulty$component),$use$transac,onal$seman,cs$(ACID$proper,es),$

prevent$system$excep,ons$from$occurring.$

Tactics for modifiabilityReduce&size&of&the&module,&for&example&by&spli7ng&module&(to&reduce&the&average&cost&of&future&

changes)&

Increase&seman>c&cohesion&of&the&module&(by&ensuring&that&the&a&responsibili>es&serving&the&same&purpose&are&placed&in&the&same&

module)&

Reduce&coupling&through&encapsula>on&(by&providing&explicit&interfaces&and&hiding&internal&details),&

introducing&intermediate&dependencies&(e.g.,&introduce&

dynamic&lookup&of&services&with&SOA&using&directory&as&an&intermediary)&&&

Tactics for performanceControl'resource'demand'through'requiring'smaller'demand'on'resources'to'service'the'events;'for'instance,'reducing'the'sampling'

frequency'(for'capturing'environmental'data),'limi;ng'event'response'(by'queuing'the'events),'

priori;zing'events'(by'ranking'the'events'according'to'their'importance'and'processing'

them),'reducing'overheads'(by'consuming'lesser'resources),'bound'execu;on';mes,'and'increase'

resource'efficiency.'

Manage'the'resources'more'effec;vely'by'increasing'resources,'introducing'concurrency,'maintaining'mul;ple'copies'of'computa;on,'

bounding'queue'sizes,'and'scheduling'resources.''

Tactics for securityDetect%a'acks%by%looking%for%known%pa'erns%of%intrusion,%detec8ng%service%denial,%

verifying%message%integrity%before%using%them,%detec8ng%message%delay%(to%detect%man=

in=the=middle%a'acks).%

Resist%a'acks%by%iden8fying,%authen8ca8ng,%and%authorizing%actors%(note:%actors%are%sources%of%external%input%to%the%system),%limi8ng%access%to%resources,%and%limi8ng%exposure%of%the%system.%

React%to%a'acks%when%an%a'ack%is%underway%by%revoking%access,%

lock%computer,%or%inform%relevant%actors.%%

Tactics for testabilityControl'and'observe'system'state'by'

providing'specializing'interfaces,'record/playback'faults,'localize'state'storage'(instead'of'distribu;ng'the'state),'

abstract'input'data'sources,'sandbox'(by'isola;ng'the'system'from'the'real'world),'and'introduce'executable'asser;ons'(to'check'if'the'program'is'in'a'faulty'state)'

Limit'complexity'(by'reducing'cyclic'dependencies,'limi;ng'dependencies'to'

external'components,'etc;'in'OO'systems,'limit'depth'of'inheritance'tree,'reduce'dynamic'calls;'and'having'high'

cohesion,'low'coupling'and'separa;on'of'concerns);'also'limit'nonCdeterminism.'

InFusion/InCode

PMD CPD

ArchiMate

Source: http://www.archimatetool.com/img/archi_out.png

Sonarqube

Sonarqubehttp://www.sonarqube.org

ArgoUML

Source: http://a.fsdn.com/con/app/proj/argouml/screenshots/52103.jpg

Nitric

“Cities grow, cities evolve, cities have parts that simply die while other

parts flourish; each city has to be renewed in order to meet the needs of its populace… Software-intensive systems

are like that. They grow, they evolve, sometimes they wither away, and

sometimes they flourish…”

Grady Booch in the foreword for “Refactoring for Software Design Smells: Managing Technical Debt”, Girish Suryanarayana, Ganesh Samarthyam, Tushar Sharma, Morgan Kaufmann/Elsevier, 2014.

CodeCity tool

Code Query Language (NDepend, Architect, …)

Look at the world differently for creative design solutions

Who coined the term

“code smell”?

Hint: He also originated the

terms TDD and XP

Kent Beck

Who coined the acronym “SOLID”?

(as in SOLID principles)

Hint: He is the author of the book

“Working effectively with legacy code”

Michael Feathers

S Single Responsibility Principle

Every object should have a single responsibility and that should be encapsulated by the class

O Open Closed Principle Software should be open for extension, but closed for modification

L Liskov’s Substitution Principle

Any subclass should always be usable instead of its parent class

I Interface Segregation Principle

Many client specific interfaces are better than one general purpose interface

D Dependency Inversion Principle

Abstractions should not depend upon details. Details should depend upon abstractions

Who coined the term “technical

debt”?

Hint: He is the creator of “wiki”

Ward Cunningham

When,duetoconstraints,Idesignquicklyanddirty,myprojectisloadedwithtechnicaldebt

NumberofAccessedVariables

CyclomaticComplexity

NewlyAddedService

PercentageofNewlyAddedService

Infusionwww.intooitus.com/products/infusion

Violates Single Responsibility Principle (SRP)

PublishedinJournalofObjectTechnology(Vol.12,No.2,2013)   SGGanesh,TusharSharma,GirishSuryanarayana.TowardsaPrinciple-basedClassifica4onofStructuralDesignSmells.InJournalofObjectTechnology,vol.12,no.2,2013,pages1:1–29.doi:10.5381/jot.2013.12.2.a1  URL:hLp://www.jot.fm/issues/issue_2013_06/arPcle1.pdf(openaccess)

"This is a good book about ‘Design Smells’ – actually a great book – nicely organized - clearly written with

plenty of examples and a fair sprinkling of anecdotes."

- Will Tracz (Principal Research Scientist & Fellow, Lockheed Martin)

(review in ACM SIGSOFT Software Engineering Notes)

Believe in your ideas: how small or “insignificant” it may

appear to be!

"The critical design tool for software development is a mind well educated in design principles"

- Craig Larman

Interface Segregation Principle (ISP)

Clients should not be forced to depend upon interfaces they do not use

Example of ISP violation

// using java.util.Date Date today = new Date(); System.out.println(today);

$ java DateUse Wed Dec 02 17:17:08 IST 2015

Why should we get the time and timezone details if

I only want a date (e.g., date of birth)? Can I get rid

of these parts? No!

JSR 310: Java Date and Time API

Stephen Colebourne

Example of a fix (java.time)

// using java.time.LocalDate LocalDate today = LocalDate.now();System.out.println(today);

$ java DateUse 2015-12-02

I can use (and hence depend upon) only date related functionality (not

time, zone, etc)

Example of a fix (java.time)You can use only date, time, or even timezone, and combine them as needed (in java.time)!

LocalDate today = LocalDate.now(); System.out.println(today); LocalTime now = LocalTime.now(); System.out.println(now);

LocalDateTime todayAndNow = LocalDateTime.now(); System.out.println(todayAndNow);

ZonedDateTime todayAndNowInTokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo")); System.out.println(todayAndNowInTokyo);

2015-12-02 17:37:22.647 2015-12-02T17:37:22.648 2015-12-02T21:07:22.649+09:00[Asia/Tokyo]

More types from java.time

Principles*

Abstrac/on*

Encapsula/on*

Modulariza/on*

Hierarchy*

Know and apply design principles

How to separate:a) code generation logic

from node types?b) how to support different

target types?

class Plus extends Expr { private Expr left, right; public Plus(Expr arg1, Expr arg2) { left = arg1; right = arg2; } public void genCode() { left.genCode(); right.genCode(); if(t == Target.JVM) { System.out.println("iadd"); } else { // DOTNET System.out.println("add"); } }}

class Plus extends Expr { private Expr left, right; public Plus(Expr arg1, Expr arg2) { left = arg1; right = arg2; } public Expr getLeft() { return left; } public Expr getRight() { return right; } public void accept(Visitor v) { v.visit(this); }}

class DOTNETVisitor extends Visitor { public void visit(Constant arg) { System.out.println("ldarg " + arg.getVal()); } public void visit(Plus plus) { genCode(plus.getLeft()); genCode(plus.getRight()); System.out.println("add"); } public void visit(Sub sub) { genCode(sub.getLeft()); genCode(sub.getRight()); System.out.println("sub"); } public void genCode(Expr expr) { expr.accept(this); }}

Source: “Design Patterns: Elements of Reusable Object-Oriented Software”, Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides, Addison-Wesley,1994

❖ Many distinct and unrelated operations need to be performed on objects in an object structure, and you want to avoid “polluting” their classes with these operations

Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the

elements on which it operations

❖ Create two class hierarchies: ❖ One for the elements

being operated on❖ One for the visitors that

define operations on the elements

{ mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "printOne", "()V", null, null); mv.visitCode();

mv.visitFieldInsn(GETSTATIC, "java/lang/System", "err", "Ljava/io/PrintStream;"); mv.visitLdcInsn("CALL println"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;"); mv.visitLdcInsn("Hello World"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

mv.visitFieldInsn(GETSTATIC, "java/lang/System", "err", "Ljava/io/PrintStream;"); mv.visitLdcInsn("RETURN println"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

mv.visitInsn(RETURN); mv.visitMaxs(2, 0); mv.visitEnd(); }

Use of visitor pattern in ASM tool (coding example of usage)

source: http://web.cs.ucla.edu/~msb/cs239-tutorial/

Apply relevant design patterns for creating high-quality designs

Extract Superclass

Modularize JDK & JRE

Hide platform internal details such as sun.misc

Provide a module system for Java developers

Reference: http://paulbakker.io/java/java-9-modularity/

Perform periodic refactoring (floss or root canal)

When,&due&to&constraints,&I&design&quickly&and&dirty,&my&project&is&loaded&with&technical&debt&

Sonarqubehttp://www.sonarqube.org

Use technical debt approach to get buy-in for refactoring

Desirable relationship between architect and manager: partnership

Steve Jobs is viewed as an excellent speaker, business person, and leader. But

not much as an architect. He is an excellent architect.

In the movie Steve Jobs, he gives an example of a music composer. The composer directs the

people and focuses on the orchestra.

That is the case with a software architect as well.

So, what’s next?

Examples from Open Source architectures

• Architecture descriptions from well-known open source software from key contributors

• You can get insights on the architecture from practical illustrations

http://www.aosabook.org/en/index.html

Practical book on SA

• Useful to get an overview of software architecture

• Especially useful if you are a programmer

• Complete presentation available here.

Good first book on SA

• Shares practical experiences in architecting enterprise IT systems

• If you want to learn about enterprise architecture, read this

SEI’s book on SA

• Good coverage of Attribute Driven Design, Architecture Trade-off Analysis Method, Quality Attributes, etc

• If you want an in-depth understanding, read this

In-depth treatment on SA• Covers a wide range of

topics in detail (stypes, modelling, visualisation, analysis, etc)

• Perhaps the most comprehensive/in-depth discussion on important SA topics

• Slides available online here

THE book on design patterns

• One of the earliest and best books on design patterns

• Presents a catalog of 23 design patterns • Classified as creational,

structural, and behavioral patterns

THE book on architectural patterns

• One of the earliest and best books on architectural patterns

• Presents a catalog of architectural patterns with detailed discussion • Referred to as POSA

book • First book in the series

of books on patterns/styles

Anti-patterns in development,

architecture, …• A practical book that

covers anti-patterns in software architectures as well as projects

• Important to know anti-patterns so that we can avoid them

Architectural refactoring is

tough!• The focus is on refactoring

techniques, tools, and processes in the large-scale (i.e., architectural level)

• Covers architectural smells as well

Getting a systems

perspective • Emphasises on working with

stakeholders, and using viewpoints and perspectives

• Read this if you are looking for gaining an in-depth understanding of working with stakeholders and using viewpoints and perspectives

An early take on SA

• Provides a good overview of architectural patterns

• If you are interested in architectural styles, tools, languages and notations, etc, read this

Tips/techniques

perspective on SA

• Provides a collection of advices from working architects

• If you are already an architect and want to know best practices, read this

And don’t forget ours!Forewords by

Grady Booch and Dr. Stephane Ducasse

Upcoming bootcamps

Mod. Sw. Arch (5 Nov) SOLID Principles (19 Nov)IoT (26 Nov)S/w Arch (10 Oct)

What were your key takeaways?

Image Credits• http://it-ebooks.info/images/ebooks/3/restful_web_services_cookbook.jpg • http://southfloridaclassicalreview.com/wp-content/uploads/

2012/11/03THECLEVELANDORCHESTRA-CPJ.jpg • http://www.ndepend.com/NS/images/CodeQuery.jpg • https://www.toadworld.com/cfs-file/__key/communityserver-blogs-components-

weblogfiles/00-00-00-00-57/DN_2D00_4a.jpg • http://d152tffy3gbaeg.cloudfront.net/2015/02/AIBA-World-Boxing-

Championships.jpg • http://www.lucidica.com/wp-content/uploads/2014/03/www.jpg • http://restfulwebapis.org/images/rws-cover.jpg • http://akamaicovers.oreilly.com/images/0636920021575/cat.gif • http://it-ebooks.info/images/ebooks/6/pro_rest_api_development_with_node.js.jpg • https://www.packtpub.com/sites/default/files/9781783285754.jpg • https://www.packtpub.com/sites/default/files/

B04843_RESTful%20Web%20Services%20with%20Scala_.jpg • http://i.ndtvimg.com/i/2015-02/sholay-still_640x480_61423213425.jpg

ganesh@codeops.tech @GSamarthyam

www.codeops.tech slideshare.net/sgganesh

+91 98801 64463 bit.ly/sgganesh