A presentation I gave for Boston Selenium User Meetup Group on Selenium Grid. Jan. 25, 2011

1. Selenium Grid
Kevin Menard
Maintainer, Selenium Grid
Founder, Mogotest

2. What is Selenium Grid?
• Maintain a cluster of Selenium RC servers
• Configure tests for different environments
• Parallelize your tests

3. How Does it Work?
Selenium Grid Hub Selenium Grid Node Selenium RC Server
Selenium Grid Node Selenium RC Server
host_a
Client
Client Selenium Grid Node Selenium RC Server
Client
Client
host_b

4. How Does it Work?
Selenium Grid Hub Selenium Grid Node Selenium RC Server
Selenium Grid Node Selenium RC Server
host_a
Client
Client Selenium Grid Node Selenium RC Server
Client
Client
host_b

5. How Does it Work?
Selenium Grid Hub Selenium Grid Node Selenium RC Server
Selenium Grid Node Selenium RC Server
host_a
Client
Client Selenium Grid Node Selenium RC Server
Client
Client
host_b

6. Environments
• Map descriptive names to browser strings
• Configured in Selenium Grid Hub
hub:
environments:
- name: "linux_firefox_3_6"
browser: "*firefox /opt/firefox-3.6/firefox-bin"
- name: "windows_firefox_3_5"
browser: "*firefox"
- name: "windows_firefox_3_6"
browser: "*firefox"

7. Starting the Hub
• Edit grid_configuration.yml
Rake:
$ rake hub:start
$ BACKGROUND=true nohup rake hub:start &>/dev/null
ant:
$ ant launch-hub
$ nohup ant launch-hub >> log_file 2>&1

8. Selenium Grid Console
• Open http://localhost:4444/console

9. Starting Up a Node
Rake:
$ rake rc:start
$ DISPLAY=:99.0 BACKGROUND=true HOST=host_b PORT=5000
ENVIRONMENT=linux_firefox_3_6 HUB_URL='http://hub_host:4444'
SELENIUM_ARGS='-ensureCleanSession -noBrowserSessionReuse'
nohup rake rc:start &>/dev/null
ant:
$ ant launch-remote-control
$ DISPLAY=:99.0 nohup ant -Dhost=host_b -Dport=5000
-Denvironment=linux_firefox_3_6 -DhubURL='http://hub_host:4444'
-DseleniumArgs='-ensureCleanSession -noBrowserSessionReuse'
launch-remote-control >> log_file 2>&1

10. Node Registration
1. Node connects to hub
Selenium Grid Node Selenium Grid Hub
environment windows_firefox_3_6
host host_b
port 5000

11. Node Registration
1. Node connects to hub
Selenium Grid Node Selenium Grid Hub
environment windows_firefox_3_6
host host_b
port 5000
2. Hub adds node to environment queue
windows_chrome windows_firefox_3_6
host_c:5000 host_a:5000
linux_firefox_3_6 host_a:5001
host_d:5000 host_b:5000

12. Available Node in
Console

13. Client Connection
• Client connects with environment name as
browser string
• Hub looks up by environment & reserves a
node
• Blocks until one is available
• Client communicates with hub at all times
• Hub forwards traffic to correct node

14. Client Connection Code
Old: New:
require 'rubygems' require 'rubygems'
require 'selenium/client' require 'selenium/client'
browser = browser =
Selenium::Client::Driver.new Selenium::Client::Driver.new
:host => 'localhost', :host => 'localhost',
:port => 4444, :port => 4444,
:browser => '*firefox', :browser => 'linux_firefox_3_6',
:url => 'http://mogotest.com/' :url => 'http://mogotest.com/'
browser.start_new_browser_session browser.start_new_browser_session
browser.open 'http://mogotest.com/' browser.open 'http://mogotest.com/'
browser.close_current_browser_session browser.close_current_browser_session

15. Makes Testing Simpler
• Client always connects to known
endpoint
• Hub takes care of browser allocation
• Nodes can be added dynamically
• Hub handles bad nodes

16. Grid Resiliency
• Hub can send heartbeat requests to node to
tell if it has gone down
• Hub can gracefully kill idle sessions
• Hub can kill sessions that take too long to
create

17. Parallel Testing
• Need a way to execute in parallel
• Java: TestNG or parallel-jUnit
• Ruby: DeepTest
• Python: nose
• Need a way to parameterize your tests for
each node’s environment
• Your tests must maintain their own state

18. Shortcomings
• Selenium 1 API compatible only
• Using an old version of Selenium RC at that
• 1 request per RC
• Doesn’t scale vertically very well
• Historically has had multi-threaded problems
• Fixed as of 1.0.8

19. Selenium Grid’s Future
• Combine Selenium Grid & RC
• De facto single-node grid
• Grid available out of the box
• Auto-discovery of other nodes on network

20. Selenium Grid 2.0
• Proposal on dev list for new grid 2.0
• Project rewrite by François Reynaud
• Supports Selenium 1 & 2 APIs
• Nicer Web interface
• Very extensible with callback points &
listeners

21. Selenium Grid 2.0
Listeners
• Possible uses
• Priority queue for test execution
• Stat tracking
• OS environment preparation

22. Conclusion
• Selenium Grid is alive and well
• 4 releases in the last 9 months
• Pushing towards a Selenium 2
compatible grid
• If you have time, please review the
proposed new grid code

23. Resources

24. Resources
• Project:
• Source: http://github.com/nirvdrum/selenium-grid
• Issues: http://selenium.googlecode.com/
• Blog: http://seleniumhq.wordpress.com/
• Personal:
• Twitter: @nirvdrum
• Email: kevin@mogotest.com