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'

Thank you! Tired to wait when they will create normal docker network for CI containers and services...

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