Building Modular Cloud Apps with OSGi

283 Pages·2013·2.62 MB·English

by  Paul Bakker

Building Modular Cloud Apps
with OSGi
Paul Bakker
Bert Ertman
Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo
DEDICATION
To Qiushi, my love, for supporting all my crazy ideas and always being there for me.
— Paul Bakker
To Jorien, my incredible wife, and to Amber, my beautiful and joyful daughter. Thank you girls for
supporting me throughout my career and for putting up with me. I love you!
— Bert Ertman
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Preface
The increasing complexity of software systems, together with the agile way in
which we develop and evolve them today, demand an approach that makes the
architecture of such systems deal with change. The solution to this challenge is
called modularity. Modularity is a core design principle that makes code easier
to understand and maintain by splitting it into small, isolated modules. This is
not a new concept, but becomes more relevant each day. A modular code base
lets us change, refactor, or simply replace code of modules without breaking
other parts of the system. This makes modularity the ultimate agile tool.
Bringing modularity from the design to the runtime is not always easy and
straightforward and cannot be done with plain Java alone. The only mature
modularity solution for Java is OSGi. Over the years, OSGi has had the
reputation of being too complex and difficult to use. Recently a lot has changed
in the area of tooling and frameworks, however, bringing it on par with the
development experience of traditional development stacks. With this we can
focus on writing code while keeping an architectural focus on modularity.
This book describes how to apply those tools and techniques available today, and
gives pragmatic insights into getting up and running with the required
technology in no time. Using easy to understand, concise, but real-world code
samples, we explore the application of modularity toward a new breed of web
applications; software as a service over the Internet, more affectionately known
as cloud applications. Along the way, we address typical cloud-age topics such
as RESTful Web Services, NoSQL, Provisioning, Elasticity, Auto-Scaling, Hot
Updates, and Automated Failover.
Who Should Read This Book
Primarily, this book is targeted to experienced enterprise Java developers who
have a keen interest in modularity and who are looking for solutions to
overcome some of today’s most advanced software development problems: how
to deal with change and how to manage complexity in a code base. The authors
of this book use the tools and techniques described throughout the book in
everyday development and have put some sophisticated cloud applications in
production using them. A significant part of what you will learn here is based
upon OSGi. We will focus on practical advice, rather than the more theoretical
approach commonly found in other books and resources.
The book will also be useful to developers who have tried using OSGi in the
past, but for some reason got stuck. Because OSGi is not a product owned by a
single vendor, it is sometimes hard to find hands-on, to-the-point information on
how to get things working. To those readers, this book can be an approachable
and practical guide to become unstuck and get things going again. By no means
is this book a complete OSGi reference, but it does contain everything that you
need to know in order to build sophisticated applications in the cloud age.
How This Book Is Organized
This book is organized into three parts. Part I introduces the concepts of
modularity from a high-level perspective and translates these to actual
implementation details. Part II focuses on developing cloud applications and the
tools and technologies required. Part III deals with deploying these applications
to production and setting up advanced cloud infrastructure capabilities such as
auto-scaling and failover.
Additionally, Appendix A describes an example application that puts everything
from this book together in a showcase. The code of this application is hosted
online, and the appendix contains instructions on how to get it.
Conventions Used in This Book
The following typographical conventions are used in this book:
Italic
Indicates new terms, URLs, email addresses, filenames, and file extensions.
Constant width
Used for program listings, as well as within paragraphs to refer to program
elements such as variable or function names, databases, data types,
environment variables, statements, and keywords.
Constant width bold
Shows commands or other text that should be typed literally by the user.
Constant width italic
Shows text that should be replaced with user-supplied values or by values
determined by context.
TIP
This icon signifies a tip, suggestion, or general note.
WARNING
This icon indicates a warning or caution.
Using Code Examples
This book is here to help you get your job done. In general, if example code is
offered with this book, you may use it in your programs and documentation. You
do not need to contact us for permission unless you’re reproducing a significant
portion of the code. For example, writing a program that uses several chunks of
code from this book does not require permission. Selling or distributing a CD-
ROM of examples from O’Reilly books does require permission. Answering a
question by citing this book and quoting example code does not require
permission. Incorporating a significant amount of example code from this book
into your product’s documentation does require permission.
We appreciate, but do not require, attribution. An attribution usually includes the
title, author, publisher, and ISBN. For example: “Building Modular Cloud Apps
with OSGi by Paul Bakker and Bert Ertman (O’Reilly). Copyright 2013 Paul
Bakker and Bert Ertman, 978-1-449-34515-0.”
You can download the full source code from GitHub. For more detailed
instructions on downloading the code, please see the section Finding and
Running the Source Code.
If you feel your use of code examples falls outside fair use or the permission
given above, feel free to contact us at [email protected].
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Acknowledgments
A number of individuals share the credit for this book’s development and
delivery. First and foremost, many thanks to O’Reilly for trusting in us and
providing us the opportunity to write this book. The team provided excellent
support throughout the editing, reviewing, proofreading, and publishing process.
The authors would like to express their gratitude to the many people who helped
or provided support in this journey. In particular, we would like to thank Meghan
Blanchette, our editor, who provided us with excellent editorial help throughout
all the stages of writing, helping with interim reviews, providing feedback on
content and styling, and connecting us to the rest of team at O’Reilly.
The detailed proofreading by Marcel Offermans and Arun Gupta ensured that the
material was technically accurate and true to the topics of the book. Their vast
experience and knowledge showed in the depth of their comments.
Finally, we would like to thank Luminis, our employer, for its encouragement
and for providing us with trust and resources to combine writing this book with
our daily jobs.