Mocked up gitlab config for running selenium in a linked container

.gitlab-ci.yml

# Custom docker image which exposes 8080
image: lafayette/hoth:5.5

services:
  - selenium/standalone-chrome:latest

before_script:
  # Use 0.0.0.0 instead of localhost to allow external connections
  - php -S 0.0.0.0:8080 -t ../ &> /dev/null &

job1:
  script:
    # Detect the IP and tell behat about it
    - export BEHAT_IP=`ip addr show eth0 | grep -Po 'inet \K[\d.]+'`
    - sed -i -e "s/localhost/$BEHAT_IP/" behat.yml
    - vendor/bin/behat --format progress

behat.yml

default:
    autoload:
        - %paths.base%/features/bootstrap
    suites:
        default:
            contexts:
                - YourContextHere
    extensions:
        Behat\MinkExtension:
            base_url: 'http://localhost:8080'
            browser_name: 'chrome'
            sessions:
                default:
                    selenium2:
                        wd_host: 'http://selenium__standalone-chrome:4444/wd/hub'

Another thank you! This was VERY tricky to figure out! GitLab's magic networking is definitely making things more difficult here. Two additional things I needed to get this working:

• Instead of ip addr show eth0 | grep -Po 'inet \K[\d.]+' I used hostname -I | awk '{print $1}' because iproute2 is not installed on default PHP images.
• I also had proxy servers in my environment. I had to add the IP address to the NO_PROXY variable.

Resulting in the following additions to the script section:

    - export LOCAL_IP_ADDRESS=`hostname -I | awk '{print $1}'`
    - export NO_PROXY=localhost,$LOCAL_IP_ADDRESS
    - sed -i -e "s/localhost/$LOCAL_IP_ADDRESS/" behat.yml