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Using WebPagetest
Rick Viscomi, Andy Davies, and Marcel Duran
Boston
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Using WebPagetest
by Rick Viscomi, Andy Davies, and Marcel Duran
Copyright © 2010 Rick Viscomi, Andy Davies and Marcel Duran. All rights reserved.
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Table of Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Part I. Basic Use Cases
1. “How fast is my page?”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Measure What Matters 3
Synthetic vs RUM 4
2. “What is slowing down my page?”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Running a Simple Test 7
Reading a Waterfall 12
Waterfall Slope 18
Connection View 21
Common Antipatterns 22
WebPagetest Grades 27
First Byte Time 28
Keep-Alive Enabled 29
Compress Transfer 30
Compress Images 30
Progressive JPEGs 30
Cache Static Content 31
Effective Use of CDN 31
3. Cache Optimization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Enabling Repeat View 34
Analyzing Cachability 36
Heuristic Caching 37
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4. Comparing Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Perceived Performance 41
Capture Video 42
Filmstrip and Video 43
Speed Index 48
Summary 52
Part II. Intermediate Use Cases
5. Simulating Real Users. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Identifying Demographics 58
Popular Pages 61
Device and Browser 62
Geographic Location 66
Connection Speed 69
6. Mobile Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Desktop Emulation 75
Traffic Shaping 79
Native Devices 80
7. Scripting Preconditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Flow View 84
logData and navigate 85
Authentication 86
HTTP Basic Authentication 87
DOM Manipulation 88
Setting Cookies 89
8. SPOF Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Blackhole Rerouting 93
setDns 94
SPOF Tab 96
Blocking Requests 98
Part III. Advanced Use Cases
9. API. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Getting started 103
Requesting a key 103
Running tests 105
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Simple example test 105
Advanced example test 107
Reading results 108
Polling test results 110
Pingback test results 111
Reading beyond results 112
10. Continuous Integration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Node.js wrapper 113
Installing WebPagetest Node.js wrapper 114
Choosing your WebPagetest server 114
Specifying the API Key 115
Running tests and reading results 115
WebPagetest Node.js wrapper extra feature: RESTful Proxy (Listener) 119
Running proxy from Node.js module 120
Asserting metrics from test results 120
JSON test specs 120
Defining assertion comparison 121
Setting default operations and labels 122
Available output text template tags 123
Avaliable assertion operations 123
Overriding labels 123
Specifying test reporter 123
Test Specs examples 124
Jenkins integration 125
Configuring Jenkins 125
Travis-CI integration 126
Configuring Travis-CI 126
11. Tracking Performance over Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Public vs Private Instance 129
Grunt-WPT 130
ShowSlow 131
Long term trending 131
Logging Results to a File 132
Splunk 132
HTTP Archive 133
12. Private Instances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
How does WebPagetest work? 136
Using the Pre-Configured AWS AMI 137
Create an AWS User with Relevant Permissions 137
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Configure and Launch AWS Instance 138
Creating your own local installation 140
Desktop Test Agents 142
Mobile Test Agents 146
Install NodeJS Agent 147
Add test devices 147
Bandwidth shaping 151
Remote Test Agents 152
Private Instance Only Features 153
Bulktest 153
Custom Metrics 155
Day-to-Day Management 155
Monitoring Queues and Test Agents 155
Archiving Old Tests 157
Updating an Instance 158
Troubleshooting 158
Contributing 160
A. Reference guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
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Preface
Who Should Read This Book
• independent site owners
• web developers
• performance engineers
Goals of This Book
This book will teach beginner users of WebPagetest how to run and analyze tests. It will
show intermediate users how to use scripting to create more sophisticated test scenarios,
how to integrate it into their everyday processes and finally how to install their own
instance of WebPagetest for a controlled testing environment
A Word on Web Performance Today
We all know bad web performance when we see it. When something takes too long to
load or become interactive we start to get bored, impatient, or even angry. The speed of
a web page has the ability to evoke negative feelings and actions from us. When we lose
interest, wait too long, or get mad, we may not behave as expected: to consume more
content, see more advertisements, or purchase more products.
The web as a whole is getting measurably slower. Rich media like photos and videos are
cheaper to download thanks to faster Internet connections, but they are more prevalent
than ever. Expectations of performance are high and the bar is being raised ever higher.
By reading this book, chances are you’re not only a user but most importantly someone
who can do something about this problem. There are many tools at your disposal that
specialize in web performance optimizations. However, none are more venerable than
WebPagetest.org. WebPagetest is a free, open source web application that audits the
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speed of web pages. In this book, we will walk you through using this tool to test the
performance of web pages so that you can diagnose the signs of slowness and get your
users back on track.
Navigating This Book
This book is organized into three primary sections: basic, intermediate, and advanced
use cases, each of which corresponds to a different level of familiarity with WebPagetest:
1. Basic use cases provide a foundation of testing experience by explaining how to run
and interpret simple tests.
2. Intermediate use cases have a deeper focus on more sophisticated test scenarios,
some of which may require scripted commands to configure how the tests are ex‐
ecuted.
3. Advanced use cases describe lower-level capabilities typically required by special
test environments including the API and private instances.
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 deter‐
mined by context.
This icon signifies a tip, suggestion, or general note.
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This icon indicates a warning or caution.
Using Code Examples
Supplemental material (code examples, exercises, etc.) is available for download at
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