Xvfb plugin to run multiple job instances concurre

Question

I have a job in Jenkins that runs UI tests written in Selenium. The job can run multiple instances of it concurrently. I am running into a problem while trying to use Xvfb (the Xvfb plugin or otherwise).

Using the Xvfb plugin

The configuration is as below. The plugin assigns the same display port to 2 concurrent job instances, and then one fails.

From the Xvfb log (note displayfd is 2 and screen is 0 in both cases):

Xvfb starting$ /usr/bin/Xvfb -displayfd 2 -screen 0 1024x758x16 -fbdir /srv/jenkins/xvfb-86-2156913754362856583.fbdir
Xvfb starting$ /usr/bin/Xvfb -displayfd 2 -screen 0 1024x758x16 -fbdir /srv/jenkins/xvfb-87-5845090375656014678.fbdir

One of the above 2 job instances fails. The failure message is this:

02:11:51 _XSERVTransSocketINETCreateListener: ...SocketCreateListener() failed
02:11:51 _XSERVTransMakeAllCOTSServerListeners: server already running

How can this error be fixed so that the concurrent instances run without any issue?

Further, I wonder how Xvfb plugin does the association of the display to the running browser instances (Firefox in this case). Does it do export DISPLAY=:xx internally, where xx = the display port as computed by the plugin?

Command line (not using Xvfb plugin)

The second way I tried is not to use the plugin and run Xvfb directly using the CLI. I used the Jenkins env variable BUILD_NUMBER to ensure unique display association to the job instance.

export DISPLAY=:${BUILD_NUMBER}
Xvfb :${BUILD_NUMBER} -screen 0 1024x768x24 &

Xvfb starts up fine in both job instances, but the tests fail with this.

Failed to connect to binary FirefoxBinary(/usr/local/bin/firefox) on port 7055; process output follows: 
Error: cannot open display: 0:0

It appears the tests are still trying to use display 0:0.

Any help to fix this problem is greatly appreciated.

Answer 1

Have you tried to use Display environment variable in Jenkins, the same Xvbf has started with? In my case it worked and I followed the instructions, described in this article headless execution selenium tests in Jenkins