Selenium: difference between "role hub" and "role webdriver"? - selenium

Question

I'm using Selenium for automated testing. What's the difference between
java -jar selenium-server-standalone-2.24.1.jar -role hub
and
java -jar selenium-server-standalone-2.24.1.jar -role webdriver
?
It seems to be the same. Or is there any difference?

Answer 1

Quoting from the official wiki page:
The Hub is the central point that will receive all the test request and distribute them the the right nodes.
Regardless on whether you want to run a grid with new WebDriver functionality, or a grid with Selenium 1 RC functionality, or both at the same time, you use the same selenium-server-standalone jar file to start the nodes.
My personal thought: The node is used for Selenium 1 (RC) and webdriver for selenium 2 (webdriver). In my personal setup i use role webdriver
If the wiki is not enough, I would suggest you to join Selenium users group

Answer 2

Everything depends on the capabilities of node, below json file shows the seleniumProtocol values and based on that it reflects the RCs and Webdrivers on grid.
"capabilities":
[
{
"browserName": "*firefox",
"maxInstances": 2,
"seleniumProtocol": "Selenium"
},
{
"browserName": "*googlechrome",
"maxInstances": 2,
"seleniumProtocol": "Selenium"
},
{
"browserName": "*iexplore",
"maxInstances": 1,
"seleniumProtocol": "Selenium"
},
{
"browserName": "firefox",
"maxInstances": 5,
"seleniumProtocol": "WebDriver"
},
{
"browserName": "chrome",
"maxInstances": 5,
"seleniumProtocol": "WebDriver"
},
{
"browserName": "internet explorer",
"maxInstances": 1,
"seleniumProtocol": "WebDriver"
}
Always shows both RC and webdriver instances on grid whether we given node or webdriver on command line