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- Herausgeber: Packt Publishing
- Kategorie: Fachliteratur
- Sprache: Englisch
This book starts by explaining how Python fits into an application's architecture. As you move along, you will get to grips with architecturally significant demands and how to determine them. Later, you’ll gain a complete understanding of the different architectural quality requirements for building a product that satisfies business needs, such as maintainability/reusability, testability, scalability, performance, usability, and security.
You will also use various techniques such as incorporating DevOps, continuous integration, and more to make your application robust. You will discover when and when not to use object orientation in your applications, and design scalable applications.
The focus is on building the business logic based on the business process documentation, and understanding which frameworks to use and when to use them. The book also covers some important patterns that should be taken into account while solving design problems, as well as those in relatively new domains such as the Cloud.
By the end of this book, you will have understood the ins and outs of Python so that you can make critical design decisions that not just live up to but also surpassyour clients’ expectations.
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Seitenzahl: 591
Veröffentlichungsjahr: 2017
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Table of Contents
Software Architecture with Python
Software Architecture with Python
Copyright © 2017 Packt Publishing
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First published: April 2017
Production reference: 2060619
Published by Packt Publishing Ltd.
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ISBN 978-1-78646-852-9
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Credits
Author
Anand Balachandran Pillai
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Mike Driscoll
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About the Author
Anand Balachandran Pillai is an Engineering and Technology professional with over 18 years of experience in the software industry in Product Engineering, Software Design and Architecture and Research. He has a Bachelor's degree in Mechanical Engineering from the Indian Institute of Technology, Madras.
He has worked at companies such as Yahoo!, McAfee, and Infosys in the roles of Lead Engineer and Architect in product development teams, to build new products.
His interests lie in Software Performace Engineering, High Scalability Architectures, Security and open source communities. He often works with startups in lead technical or consulting role.
He is the founder of the Bangalore Python Users Group and a Fellow of the Python Software Foundation (PSF).
Anand is currently working as Senior Architect of Yegii Inc.
Dedicated to friends & family
About the Reviewer
Mike Driscoll has been programming in Python since 2006. He enjoys writing about Python in his blog, http://www.blog.pythonlibrary.org/. He has coauthored the Core Python refcard for DZone. He has also worked as a technical reviewer for Python 3 Object Oriented Programming, Python 2.6 Graphics Cookbook, Tkinter GUI Application Development Hotshot, and several other book. He recently wrote the book Python 101 and is working on his next book.
I would like to thank my beautiful wife, Evangeline, for always supporting me and my friends and family for all that they do to help me. And I would like to thank Jesus Christ for saving me.
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Preface
Software architecture, or creating a blueprint design for a particular software application, is not a walk in the park. The two biggest challenges in software architecture are keeping the architecture in sync, first with the requirements as they are uncovered or evolve, and next with the implementation as it gets built and evolves.
Filled with examples and use cases, this guide takes a direct approach to helping you with everything it takes to become a successful software architect. This book will help you understand the ins and outs of Python so that you can architect and design highly scalable, robust, clean, and performant applications in Python.
What this book covers
Chapter 1, Principles of Software Architecture, introduces the topic of software architecture, giving you a brief on architectural quality attributes and the general principles behind them. This will enable you to have strong fundamentals in software architectural principles and foundational attributes.
Chapter 2, Writing Modifiable and Readable Code, covers developmental architectural quality attributes, namely, modifiability and readability. It will help you gain an understanding of the architectural quality attribute of maintainability and tactics of writing code in Python to test your applications.
Chapter 3, Testability – Writing Testable Code, helps you understand the architectural quality attribute of testability and how to architect Python applications for testability. You will also learn about various aspects of testability and software testing and the different libraries and modules available in Python to write testable applications.
Chapter 4, Good Performance is Rewarding!, covers the performance aspects of writing Python code. You will be equipped with the knowledge of performance as a quality attribute in architecture and when to optimize for performance. You will learn when to optimize for performance in the SDLC.
Chapter 5, Writing Applications that Scale, talks about the importance of writing scalable applications. It discusses different ways to achieve of application scalability and discusses scalability techniques using Python. You will also learn about theoretical aspects of scalability and the best practices in the industry.
Chapter 6, Security – Writing Secure Code, discusses the security aspect of architecture and teaches you best practices and techniques of writing applications that are secure. You will understand the different security issues to watch out for and to and to architecture applications in Python that are secure from the ground up.
Chapter 7, Design Patterns in Python, gives you an overview of design patterns in Python from a pragmatic programmer's perspective, with brief theoretical background of each pattern. You will gain knowledge of design patterns in Python that are actually useful to pragmatic programmer.
Chapter 8, Python Architectural Patterns, introduces you to the modern architectural patterns in Python from a high-level perspective while giving examples of Python libraries and frameworks to realize the approaches of these patterns to solve high-level architecture problems.
Chapter 9, Deploying Python Applications, covers the aspect of easily deploying your code on remote environments or on the cloud using Python the right way.
Chapter 10, Techniques for Debugging, covers some of the debugging techniques for Python code—from the simplest, strategically placed print statement to logging and system call tracing which will be very handy to the programmer and also help the system architect to guide his team.
What you need for this book
To run most of the code samples shown in this book, you need to have Python 3 installed on your system. The other prerequisites are mentioned at the respective instances.
Who this book is for
This book is for experienced Python developers who are aspiring to become the architects of enterprise-grade applications or software architects who would like to leverage Python to create effective blueprints of applications.
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Chapter 1. Principles of Software Architecture
This is a book on Python. At the same time, it is a book about software architecture and its various attributes, which are involved in a software development life cycle.
In order for you to understand and combine both aspects, which is essential to get maximum value from this book, it is important to grasp the fundamentals of software architecture, the themes and concepts related to it, and the various quality attributes of software architecture.
A number of software engineers, taking on senior roles in their organizations, often get very different interpretations of the definitions of software design and architecture, and the roles they play in building testable, maintainable, scalable, secure, and functional software.
Though there is a lot of literature in the field, which is available both in conventional book form and on the internet; very often, the practitioners among us get a confusing picture of these very important concepts. This is often due to the pressures involved in learning the technology rather than learning the fundamental design and architectural principles underlying the use of technology in building systems. This is a common practice in software development organizations, where the pressures of delivering working code often overpowers and eclipses everything else.
A book such as this one, strives to transcend the middle path in bridging the rather esoteric aspects of software development related to its architectural quality attributes to the mundane details of building software using programming languages, libraries, and frameworks—in this case, using Python and its developer ecosystem.
The role of this introductory chapter is to demystify these concepts, and explain them in very clear terms to the reader to prepare his/her for the path towards understanding the rest of this book. Hopefully, by the end of this book, the concepts and their practical details will represent a coherent body of knowledge to the reader.
We will now get started on this path without any further ado, roughly fitting this chapter into the following sections:
Defining software architecture
There are various definitions of software architecture in the literature concerning the topic. A simple definition is given as follows:
Software architecture is a description of the subsystems or components of a software system, and the relationships between them.
The following is a more formal definition, from the Recommended Practice for Architectural Description of Software-Intensive Systems (IEEE) technology:
"Architecture is the fundamental organization of a system embodied in its components, their relationships to each other, and to the environment, and the principles guiding its design and evolution."
It is possible to get umpteen such definitions of software architecture if one spends some time searching on the web. The wordings might differ, but all the definitions refer to some core, fundamental aspects underlying software architecture.
Software architecture versus design
In the experience of the author, this question of the software architecture of a system versus its design seems to pop up quite often, in both online as well as offline forums. Hence, let us take a moment to understand this aspect.
Though both terms are often used interchangeably, the rough distinction of architecture versus design can be summarized as follows:
Software architecture is about the design of the entire system, whereas, software design is mostly about the details, typically at the implementation level of the various subsystems and components that make up those subsystems.
In other words, the word design comes up in both contexts, however, with the distinction that the former is at a much higher abstraction and at a larger scope than the latter.
There is a rich body of knowledge available for both software architecture and design, namely, architectural patterns and design patterns respectively. We will discuss both these topics in later chapters of this book.
Aspects of software architecture
In both the formal IEEE definition and the rather informal definition given earlier, we find some common, recurring themes. It is important to understand them in order to take our discussion on software architecture further:
Now that you have understood some of the core aspects of software architecture, let us briefly list some of its characteristics.
Characteristics of software architecture
All software architectures exhibit a common set of characteristics. Let us look at some of the most important ones here.
An architecture defines a structure
An architecture of a system is best represented as structural details of the system. It is a common practice for practitioners to draw the system architecture as a structural component or class diagram in order to represent the relationships between the subsystems.
For example, the following architecture diagram describes the backend of an application that reads from a tiered database system, which is loaded using an ETL process:
Example architecture diagram showing system structure
Structures provide insight into architectures, and provide a unique perspective to analyze the architecture with respect to its quality attributes.
Some examples are as follows:
An architecture picks a core set of elements
A well-defined architecture clearly captures only the core set of structural elements required to build the core functionality of the system, and which have a lasting effect on the system. It does not set out to document everything about every component of the system.
For example, an architect describing the architecture of a user interacting with a web server for browsing web pages—a typical client/server architecture—would focus mainly on two components: the user's browser (client) and the remote web server (server), which form the core elements of the system.
The system may have other components such as multiple caching proxies in the path from the server to the client, or a remote cache on the server which speeds up web page delivery. However, this is not the focus of the architecture description.
An architecture captures early design decisions
This is a corollary to the characteristics described previously. The decisions that help an architect to focus on some core elements of the system (and their interactions) are a result of the early design decisions about a system. Thus, these decisions play a major role in further development of the system due to their initial weight.
For example, an architect may make the following early design decisions after careful analysis of the requirements for a system:
Note
The first decision freezes the deployment choices of the system to a large extent to a specific OS and system architecture. The next two decisions have a lot of weight in implementing the backend APIs. The last decision freezes the programming language choices for the system.
Early design decisions need to be arrived at after careful analysis of the requirements and matching them with the constraints—such as organizational, technical, people, and time constraints.
An architecture manages stakeholder requirements
A system is designed and built, ultimately, at the behest of its stakeholders. However, it is not possible to address each stakeholder requirement to its fullest due to an often contradictory nature of such requirements. Following are some examples:
An architecture influences the organizational structure
The system structures an architecture describes, quite often have a direct mapping to the structure of the teams that build those systems.
For example, an architecture may have a data access layer which describes a set of services that read and write large sets of data—it is natural that such a system gets functionally assigned to the database team, which already has the required skill sets.
Since the architecture of a system is its best description of the top-down structures, it is also often used as the basis for the task-breakdown structures. Thus, software architecture often has a direct bearing on the organizational structures that build it:
System architecture for a search web application
The following diagram shows the mapping to the team structure which would be building this application:
An architecture is influenced by its environment
An environment imposes outside constraints or limits within which an architecture must function. In the literature, these are often called architecture in context [Ref: Bass, Kazman]. Some examples are as follows:
Architecture choices also arise from one's own education and professional training, and also from the influence of one's professional peers.
An architecture documents the system
Every system has an architecture, whether it is officially documented or not. However, properly documented architectures can function as an effective documentation for the system. Since an architecture captures the system's initial requirements, constraints, and stakeholder trade-offs, it is a good practice to document it properly. The documentation can be used as a basis for training later on. It also helps in continued stakeholder communication, and for subsequent iterations of the architecture based on changing requirements.
The simplest way to document an architecture is to create diagrams for the different aspects of the system and organizational architecture such as Component Architecture, Deployment Architecture, Communication Architecture, and the Team or Enterprise Architecture.
Other data that can be captured early include the system requirements, constraints, early design decisions, and rationale for those decisions.
An architecture often conforms to a pattern
Most architectures conform to certain sets of styles which have had a lot of success in practice. These are referred to as architectural patterns. Examples of such patterns are client-server, pipes and filters, data-based architectures, and others. When an architect chooses an existing pattern, he/she gets to refer to and reuse a lot of existing use cases and examples related to such patterns. In modern day architectures, the job of the architect comes down to mixing and matching existing sets of such readily available patterns to solve the problem at hand.
For example, the following diagram shows an example of a client-server architecture:
Example of client-server architecture
The following diagram describes another common architecture pattern, namely, the pipes and filters architecture for processing streams of data:
Example of pipe and filters architecture
We will see examples of architectural patterns later in this book.
Importance of software architecture
So far, we have discussed the fundamental principles of software architecture, and also seen some of its characteristics. These sections, of course, assumed that software architecture is important, and is a critical step of the software development process.
It is time to play devil's advocate, and look back at software architecture and ask some existential questions about it as follows:
Let us take a look at the critical insights that software architecture provides, which would otherwise be missing from an informal software development process. We are only focusing on the technical or developmental aspects of the system in the following table:
Aspect
Insight/Impact
Examples
Architecture selects quality attributes to be optimized for a system.
Aspects such as scalability, availability, modifiability, security, and so on of a system depend on early decisions and trade-offs while selecting an architecture. You often trade one attribute in favor of another.
A system that is optimized for scalability must be developed using a decentralized architecture where elements are not tightly coupled. For example: microservices, brokers.
Architecture facilitates early prototyping.
Defining an architecture allows the development organization to try and build early prototypes, which gives valuable insights into how the system would behave without having to build the complete system top down.
Many organizations build out quick prototypes of services—typically, by building only the external APIs of these services and mocking the rest of the behavior. This allows for early integration tests and figuring out interaction issues in the architecture early on.
Architecture allows a system to be built component-wise.
Having a well-defined architecture allows the reuse and assembly of existing, readily available components to achieve the functionality without having to implement everything from scratch.
Libraries or frameworks which provide ready-to-use building blocks for services.
For example: web application frameworks such as Django/RoR, and task distribution frameworks such as Celery.
Architecture helps to manage changes to the system.
An architecture allows the architect to scope out changes to the system in terms of components that are affected and those which are not. This helps to keep system changes to a minimum when implementing new features, performance fixes, and so on.
A performance fix for database reads to a system would need changes only to the DB and Data Access Layer (DAL) if the architecture is implemented correctly. It need not touch the application code at all. For example, this is how most modern web frameworks are built.
There are a number of other aspects which are related to the business context of a system, into which architecture provides valuable insights. However, since this is a book mostly on the technical aspects of software architecture, we have limited our discussion to the ones given in the preceding table.
Now, let us take on the second question:
Why not build a system without a formal software architecture?
If you've been following the arguments so far thoroughly, it is not very difficult to see the answer for it. It can, however, be summarized in the following few statements:
System versus enterprise architecture
You may have heard the term architect used in a few contexts. The following job roles or titles are pretty common in the software industry for architects:
You also may have heard the term System architect, perhaps the term Enterprise architect, and maybe, Solution architect also. The interesting question is: What do these people do?
Let us try and find the answer to this question.
An Enterprise architect looks at the overall business and organizational strategies for an organization, and applies architecture principles and practices to guide the organization through the business, information, process, and technology changes necessary to execute their strategies. The Enterprise architect usually has a higher strategy focus and a lower technology focus. The other architect roles take care of their own subsystems and processes. For example:
These specific architectural roles are all concerned with their own systems and subsystems. So, each of these roles is a System architect role.
These architects help the Enterprise architect to understand the smaller picture of each of the business domain they are responsible for, which helps the Enterprise architect to get information that will aid him in formulating business and organizational strategies.
The System architect: A System architect usually has a higher technology focus and a lower strategy focus. It is a practice in some service-oriented software organizations to have a Solution architect, who combines the different systems to create a solution for a specific client. In such cases, the different architect roles are often combined into one, depending on the size of the organization, and the specific time and cost requirements of the project.The Solution architect: A Solution architect typically straddles the middle position when it comes to strategy versus technology focus and organizational versus project scope.The following schematic diagram depicts the different layers in an organization–Technology, Application, Data, People, Process, and Business, and makes the focus area of the architect roles very clear:
Enterprise versus System architects
Let's discuss the preceding diagram a bit to understand the picture it lays out.
The System architect is pictured on the bottom-left side of the diagram, looking at the system components of the enterprise. His/her focus is on the applications that power the enterprise, their data, and the hardware and software stack powering the applications.
The Enterprise architect, on the other hand, is pictured on the top, having a top-down view of the enterprise including the business goals and the people, and not just the underlying systems that power the organization. The vertical stack of business processes connect the technical components that power the organization with its people and business components. These processes are defined by the Enterprise architect in discussion with the other stakeholders.
Now that you have understood the picture behind Enterprise and System architecture, let us take a look at some formal definitions:
"Enterprise Architecture is a conceptual blueprint that defines the structure and behavior of an organization. It determines how the organization's structure, processes, personnel and flow of information is aligned to its core goals to efficiently achieve its current and future objectives."
"A system architecture is the fundamental organization of a system, represented by its structural and behavioral views. The structure is determined by the components of the system and the behavior by the relationships between them and their interaction with external systems."
An Enterprise architect is concerned with how the different elements in an organization and their interplay is tuned towards achieving the goals of the organization in an efficient manner. In this work, he/she needs the support of not just the technical architects in the organization, but also people managing the organization, such as project managers and human resource professionals.
A Systems architect, on the other hand, is worried about how the core system architecture maps to the software and hardware architecture, and the various details of human interactions with the components in the system. His/her concern never arises above the boundaries defined by the system and its interactions.
The following diagram depicts the different focus areas and scopes of the different architect roles that we've discussed so far:
Scope and focus of various architect roles in a software organization
