Patrick Lightbody Presentation Tae Slides

Design Tips for
Dynamic UIs Under
Heavy Load

Patrick Lightbody
Founder, BrowserMob
patrick@browsermob.com

http://browsermob.com

Patrick & the ‘Mob
Open source contributor
- Apache Struts 2.0 (previously WebWork)

- Founder of OpenQA.org and SeleniumHQ.org

- Creator of Selenium Remote Control

Founder of BrowserMob
- On-demand load testing and monitoring services

- Uses real web browsers in various cloud
environments (EC2, GoGrid, Rackspace, etc)


The Problem
AJAX => Faster (Perceived) Experience
- More logic on front-end with asynchronous calls
to server logic on back-end

But when the back-end is slow or error
prone, the experience tends to be worse
- Non AJAX => Full page load => spinning “e” for IE

Most complex UIs built in isolation
- Tested on localhost (no load, infinite bandwidth)


Recent Example
Load test for a UK-based car insurance
provider
Frequent errors in which the the browser
was showing a registration form claiming
that field X was not filled out
A real head-scratcher... we were 110%
positive that field was being filled out by
the test
Finally figured it out: reproduced by hand


UI Design
First Name Patrick First Name Patrick

Last Name Lightbody Last Name Lightbody

Company BrowserMob Company BrowserMob

Email Email Email is required

Home Phone 4158305488 Home Phone (415) 830-5488

Cell Phone Cell Phone

onchange
inject form data back in

Form Form
Representation Representation
(JSON) (JSON)

Web Server


Typical Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob

Email

Home Phone

Cell Phone


Typical Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob

Email patrick@browsermob

Home Phone

Cell Phone


Typical Sequence
AJAX Request #1
First Name Patrick

Form
Last Name Lightbody Representation
(JSON)
Company BrowserMob


Home Phone
Web Server

Cell Phone


Typical Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob


Home Phone 4158305488

Cell Phone


Typical Sequence
AJAX Request #2
First Name Patrick

Form
Last Name Lightbody Representation
(JSON)
Company BrowserMob


Web Server

Cell Phone


Typical Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob


Home Phone (415) 830-5488

Cell Phone


Problem Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob

Email

Home Phone

Cell Phone


Problem Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob


Home Phone

Cell Phone


Problem Sequence
First Name Patrick
AJAX Request #1
Last Name Lightbody Form
Representation
(JSON)
Company BrowserMob


Home Phone
Web Server

Cell Phone


Problem Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob



Cell Phone


Problem Sequence
First Name Patrick
AJAX Request #2
Representation
(JSON)
Company BrowserMob


Web Server

Cell Phone


Problem Sequence
First Name Patrick

Last Name Lightbody

Company BrowserMob


Home Phone (415) 830-5488

Cell Phone


Problem Sequence
First Name Patrick
AJAX Request #1
Representation
(JSON)
Company BrowserMob


Home Phone (415) 830-5488
Web Server

Cell Phone


Problem Sequence
First Name Patrick

Last Name Lightbody
Whoops!
Company BrowserMob

Email patrick@browsermob No more Home Phone!
Home Phone (415) 830-5488

Cell Phone


Reproducing
Re-create the slowdown/error in your code
- Can be turned on/off with a “test” flag in your app

Run load tests simultaneously with
browser tests
- Run a Selenium test on loop while using JMeter

Run your browser through a network
simulator
- Simulate bandwidth, latency, response codes, etc


Mocking out Failure
Add simple if statement in the server code
that sleep for X seconds or throw an error
Attach a debugger, break on a line, and just
sit there before you resume execution
If you’re feeling especially adventurous,
make a generic “filter” for your app
- In Java this would be a “Servlet Filter”

- Could be made very advanced


public void doFilter(HttpServletRequest req,
HttpServletResponse res,
FilterChain chain)
throws IOException, ServletException {

String uri = req.getRequestURI();

Random r = new Random();
if (r.nextInt(100) > 80) {
res.sendError(500, "20% chance of failure!");
return;
}

// sleep between 0 and 5 seconds
Thread.sleep(r.nextInt(1000) * 5);

chain.doFilter(req, res);

}


Selenium During Load
Hard to predict all ways in which things can
go wrong
- Easier to simulate the ways things should go right

Run a standard load test against the REST
interfaces
- Ideally, this should “realistically” slow them down

Simultaneously, play back Selenium scripts
- Check for functionality over performance


Selenium as Load
Similar approach as before, but on steroids
Run hundreds or thousands of Selenium
scripts in parallel
- This means you need hundreds or thousands of
browsers!

- Checking performance and functionality
concurrently

Produces hyper-realistic load scenarios
and almost always uncovers unexpected
problems

How It Works


How It Works

Automatically provision
browsers from the cloud


How It Works
4000 CPU Cores
3.5TB of RAM

Automatically provision
browsers from the cloud


Network Simulators
Another approach is to run your browser
through a network simulator
Usually done via an HTTP proxy that can be
tuned to:
- Return fake error codes

- Simulate bandwidth & latency

- Drop packets

- Record network performance


Charles Proxy
Charles Proxy
- “Web Debugging Proxy Application”

- Windows, OS X, and Linux

- Cost: $50 per user w/ bulk discounts

- http://www.charlesproxy.com


BrowserMob Proxy
Announcing today: free, open source utility
Supports HTTP and HTTPS
Produces Firebug-like results for any
browser
Simulates different bandwidth, latency, and
error conditions
Available for download today!
- http://proxy.browsermob.com


Demo


Design Tips


Design for Failure
Never forget: AJAX is still a network call
- Networks fail for a lot of different reasons

- Networks can be unpredictable (ie: request #1 can
take longer than request #2)

Add hooks to AJAX requests for the
unexpected
- Write your code to store request params & retry

Test for failure too!


Be Careful w/ DOM
Only change the DOM state if it’s absolutely
necessary
- Avoid aggressive “synchronization” common in
some AJAX toolkits (ex: our form sync example)

Merge data together rather than replace
- Partial page loads (div.innerHTML = ...) is also bad

- Involves more work, but results in a much better
experience when things don’t work well


Lock the UI
Don’t give the user a chance to change
things that might also get changed by you
- In our form example: disable the form elements!

- If necessary, use a modal dialog box to lock the
entire UI

But remember: have a recovery plan!
- Test for failure and ensure that the UI unlocks
when unexpected behavior occurs


Inform the User
Always keep the user informed about what
is happening
Ideally give them an “escape hatch” if
things go terrible wrong
- Set thresholds for when to present the escape
hatch

- GMail is a good example of this

At minimum, simple “loading” indicator


Questions?
Patrick Lightbody
Founder, BrowserMob
patrick@browsermob.com

BrowserMob Proxy (Open Source)
http://proxy.browsermob.com

BrowserMob Services


Patrick Lightbody Presentation Tae Slides

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