XVFB issues when running two CI instances in parallel

Is this a Feature or Bug?

Bug

Current behavior:

When running two test instances within the GitLab CI in parallel (one dev and one prod) with the same cypress config (expect of the port) one of both jobs throws the following error:

Your system is missing the dependency: XVFB
Install XVFB and run Cypress again.
Read our documentation on dependencies for more information:
https://on.cypress.io/required-dependencies
If you are using Docker, we provide containers with all required dependencies installed.
----------

Caught error trying to run XVFB: "Your system is missing the dependency: XVFB
Install XVFB and run Cypress again.
Read our documentation on dependencies for more information:
https://on.cypress.io/required-dependencies
If you are using Docker, we provide containers with all required dependencies installed.
----------

Error: Could not start Xvfb.
----------

The jobs run headless and all requirements for the core system running in CI are installed. When I restart the job after the successful one was finished, everything works fine. I googled a bit and found this one: https://stackoverflow.com/questions/30332137/xvfb-run-unreliable-when-multiple-instances-invoked-in-parallel. Maybe this could be a hint what goes wrong?

How to reproduce:

Start two CI jobs using cypress run in parallel

• Operating System: ArchLinux with Kernel 4.15.7-1
• Cypress Version: 2.1.0

Thanks Sebastian

[cameronc56]

I’ve been experiencing similar failures when cypess is trying to detect a free port, i had --net=host on my docker image, and my jenkins host would intermittently also use port 6099 for some process, causing sporadic failures.

[brian-mann]

You likely want to split up running Cypress across two different instances - not the same instance. It is possible to do as you’re doing - but you will be maxing out the CPU and likely the RAM with just a single instance running… with two they will most definitely affect one another.

I looked at the link - and although we don’t use xvfb-run, the same scenario is likely happening. We do use lockfiles but its possible there is a race condition if you’re spawning them at the same time.