Re-Engineering Legacy Software.pdf

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brief contents

contents

preface

acknowledgments

about this book

Roadmap

Source code

Author Online

About the author

About the cover

Part 1 Getting started

1 Understanding the challenges of legacy projects

1.1 Definition of a legacy project

1.1.1 Characteristics of legacy projects

1.1.2 Exceptions to the rule

1.2 Legacy code

1.2.1 Untested, untestable code

1.2.2 Inflexible code

1.2.3 Code encumbered by technical debt

1.3 Legacy infrastructure

1.3.1 Development environment

1.3.2 Outdated dependencies

1.3.3 Heterogeneous environments

1.4 Legacy culture

1.4.1 Fear of change

1.4.2 Knowledge silos

1.5 Summary

2 Finding your starting point

2.1 Overcoming feelings of fear and frustration

2.1.1 Fear

2.1.2 Frustration

2.2 Gathering useful data about your software

2.2.1 Bugs and coding standard violations

2.2.2 Performance

2.2.3 Error counts

2.2.4 Timing common tasks

2.2.5 Commonly used files

2.2.6 Measure everything you can

2.3 Inspecting your codebase using FindBugs, PMD, and Checkstyle

2.3.1 Running FindBugs in your IDE

2.3.2 Handling false positives

2.3.3 PMD and Checkstyle

2.4 Continuous inspection using Jenkins

2.4.1 Continuous integration and continuous inspection

2.4.2 Installing and setting up Jenkins

2.4.3 Using Jenkins to build and inspect code

2.4.4 What else can we use Jenkins for?

2.4.5 SonarQube

2.5 Summary

Part 2 Refactoring to improve the codebase

3 Preparing to refactor

3.1 Forming a team consensus

3.1.1 The Traditionalist

3.1.2 The Iconoclast

3.1.3 It’s all about communication

3.2 Gaining approval from the organization

3.2.1 Make it official

3.2.2 Plan B: The Secret 20% Project

3.3 Pick your fights

3.4 Decision time: refactor or rewrite?

3.4.1 The case against a rewrite

3.4.2 Benefits of rewriting from scratch

3.4.3 Necessary conditions for a rewrite

3.4.4 The Third Way: incremental rewrite

3.5 Summary

4 Refactoring

4.1 Disciplined refactoring

4.1.1 Avoiding the Macbeth Syndrome

4.1.2 Separate refactoring from other work

4.1.3 Lean on the IDE

4.1.4 Lean on the VCS

4.1.5 The Mikado Method

4.2 Common legacy code traits and refactorings

4.2.1 Stale code

4.2.2 Toxic tests

4.2.3 A glut of nulls

4.2.4 Needlessly mutable state

4.2.5 Byzantine business logic

4.2.6 Complexity in the view layer

4.3 Testing legacy code

4.3.1 Testing untestable code

4.3.2 Regression testing without unit tests

4.3.3 Make the users work for you

4.4 Summary

5 Re-architecting

5.1 What is re-architecting?

5.2 Breaking up a monolithic application into modules

5.2.1 Case study—a log management application

5.2.2 Defining modules and interfaces

5.2.3 Build scripts and dependency management

5.2.4 Spinning out the modules

5.2.5 Giving it some Guice

5.2.6 Along comes Gradle

5.2.7 Conclusions

5.3 Distributing a web application into services

5.3.1 Another look at Orinoco.com

5.3.2 Choosing an architecture

5.3.3 Sticking with a monolithic architecture

5.3.4 Separating front end and back end

5.3.5 Service-oriented architecture

5.3.6 Microservices

5.3.7 What should Orinoco.com do?

5.4 Summary

6 The Big Rewrite

6.1 Deciding the project scope

6.1.1 What is the project goal?

6.1.2 Documenting the project scope

6.2 Learning from the past

6.3 What to do with the DB

6.3.1 Sharing the existing DB

6.3.2 Creating a new DB

6.3.3 Inter-app communication

6.4 Summary

Part 3 Beyond refactoring— improving project workflow and infrastructure

7 Automating the development environment

7.1 First day on the job

7.1.1 Setting up the UAD development environment

7.1.2 What went wrong?

7.2 The value of a good README

7.3 Automating the development environment with Vagrant and Ansible

7.3.1 Introducing Vagrant

7.3.2 Setting up Vagrant for the UAD project

7.3.3 Automatic provisioning using Ansible

7.3.4 Adding more roles

7.3.5 Removing the dependency on an external database

7.3.6 First day on the job—take two

7.4 Summary

8 Extending automation to test, staging, and production environments

8.1 Benefits of automated infrastructure

8.1.1 Ensures parity across environments

8.1.2 Easy to update software

8.1.3 Easy to spin up new environments

8.1.4 Enables tracking of configuration changes

8.2 Extending automation to other environments

8.2.1 Refactor Ansible scripts to handle multiple environments

8.2.2 Build a library of Ansible roles and playbooks

8.2.3 Put Jenkins in charge

8.2.4 Frequently asked questions

8.3 To the cloud!

8.3.1 Immutable infrastructure

8.3.2 DevOps

8.4 Summary

9 Modernizing the development, building, and deployment of legacy software

9.1 Difficulties in developing, building, and deploying legacy software

9.1.1 Lack of automation

9.1.2 Outdated tools

9.2 Updating the toolchain

9.3 Continuous integration and automation with Jenkins

9.4 Automated release and deployment

9.5 Summary

10 Stop writing legacy code!

10.1 The source code is not the whole story

10.2 Information doesn’t want to be free

10.2.1 Documentation

10.2.2 Foster communication

10.3 Our work is never done

10.3.1 Periodic code reviews

10.3.2 Fix one window

10.4 Automate everything

10.4.1 Write automated tests

10.5 Small is beautiful

10.5.1 Example: the Guardian Content API

10.6 Summary

index

Symbols

Numerics

Chris Birchall M A N N I N G

Re-Engineering Legacy Software

Re-Engineering Legacy Software CHRIS BIRCHALL M A N N I N G SHELTER ISLAND

For online information and ordering of this and other Manning books, please visit www.manning.com. The publisher offers discounts on this book when ordered in quantity. For more information, please contact Special Sales Department Manning Publications Co. 20 Baldwin Road PO Box 761 Shelter Island, NY 11964 Email: orders@manning.com ©2016 by Manning Publications Co. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by means electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in the book, and Manning Publications was aware of a trademark claim, the designations have been printed in initial caps or all caps. Recognizing the importance of preserving what has been written, it is Manning’s policy to have the books we publish printed on acid-free paper, and we exert our best efforts to that end. Recognizing also our responsibility to conserve the resources of our planet, Manning books are printed on paper that is at least 15 percent recycled and processed without the use of elemental chlorine. Manning Publications Co. 20 Baldwin Road PO Box 761 Shelter Island, NY 11964 Development editor: Karen Miller Technical development editor: Robert Wenner Copyeditor: Andy Carroll Proofreader: Elizabeth Martin Technical proofreader: René van den Berg Typesetter: Dottie Marsico Cover designer: Marija Tudor ISBN 9781617292507 Printed in the United States of America 1 2 3 4 5 6 7 8 9 10 – EBM – 21 20 19 18 17 16

brief contents PART 1 GETTING STARTED ........................................................1 1 ■ Understanding the challenges of legacy projects 3 2 ■ Finding your starting point 16 PART 2 REFACTORING TO IMPROVE THE CODEBASE..................45 3 ■ Preparing to refactor 47 4 ■ Refactoring 67 5 ■ Re-architecting 103 6 ■ The Big Rewrite 128 PART 3 BEYOND REFACTORING—IMPROVING PROJECT WORKFLOW AND INFRASTRUCTURE...............................................147 7 ■ Automating the development environment 149 8 ■ Extending automation to test, staging, and production environments 165 Modernizing the development, building, and deployment of 9 ■ legacy software 180 10 ■ Stop writing legacy code! 197 v

contents xiii preface acknowledgments about this book xiv xvi PART 1 GETTING STARTED . .......................................... 1 1 Understanding the challenges of legacy projects 3 1.1 Definition of a legacy project 4 Characteristics of legacy projects 4 ■ Exceptions to the rule 5 1.2 Legacy code 6 Untested, untestable code 6 ■ Inflexible code 8 ■ Code encumbered by technical debt 9 1.3 Legacy infrastructure 10 Development environment 10 ■ Outdated dependencies 11 Heterogeneous environments 12 1.4 Legacy culture 13 Fear of change 13 ■ Knowledge silos 14 1.5 Summary 15 vii

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