Selenium Grid

Abstract

Based on the selenium standalone server

Allows you to scale by distributing tests on several machines ( parallel execution )

First of all you have to launch the hub using the role hub

> docker run -d -p 4444:4444 --name selenium-hub selenium/hub:3.141.59-hafnium
--
> java -jar selenium-server-standalone-3.9.jar -role hub

After that you can launch the nodes that communicate with the hub and perform the requested actions by the hub using the role node

> docker run -d --link selenium-hub:hub -v /dev/shm:/dev/shm selenium/node-chrome:3.141.59-hafnium

> docker run -d --link selenium-hub:hub -v /dev/shm:/dev/shm selenium/node-firefox:3.141.59-hafnium

---
> java -jar selenium-server-standalone-3.9.jar -role node -hub http://localhost:4444/grid/register

Jenkins

Jenkins allows you to handle Selenium Grid in the right way using the Selenium Plugin

This plugin sets up Selenium Grid in the following way

On master, Selenium Grid Hub is started on port 4444, unless configured otherwise in Jenkins global configurations. This is where all your tests should connect to.
For each slave, necessary binaries are copied and Selenium RCs are started.
RCs and the Selenium Grid Hub are hooked up together automatically.

Grid can also accept additional nodes launched outside Jenkins.

Local environment

Setting up a master slave installation in local to test selenium grid. All the installation is based on a list of docker container, one for jenkins and the other for the selenium nodes.

In order to let all the container talk to each other we have to insert a new entry in the hosts file with the IP address of the docker Jenkins just launched using a name you want

172.18.0.2 jenkins

Create a docker network to group all the docker containers

> docker network create grid

and then launch a Jenkins server using docker

> docker run \
    -u root \
    --rm \
    --net grid \
    -p 8080:8080 \
    -p 50000:50000 \
    -p 4444:4444 \
    -v jenkins-data:/var/jenkins_home \
    -v /var/run/docker.sock:/var/run/docker.sock \
    --name jenkins \
    jenkinsci/blueocean

Once the Jenkins master is uop and running we have to in install the Selenium plugin for Jenkins. In this way we are exposing the jenkins server, the agents and the Selenium grid.

You have to change the URL of the jenkins server from http://localhost:8080 to http://jenkins:8080

Afer the start-uo of Jenkins master we can start the docker image of a slave node in this way (for chrome)

> docker run \
  --net grid \
  -e HUB_HOST=jenkins \
  -v /dev/shm:/dev/shm selenium/node-chrome:3.141.59-iron

and for firefox

> docker run \
  --net grid \
  -e HUB_HOST=jenkins \
  -v /dev/shm:/dev/shm selenium/node-firefox:3.141.59-iron

So now we ca start some selenium slave in order to attach to the hub and the hub is inside Jenkins because we have installed the selenium plugin

Example

Created a little example test based on nightwatch and nightwatch cucumber (http://nightwatchjs.org/)

The most important thing is to configure in the right way nightwatch in order to let the test run in the node test of the grid. So take a look to the file nightwatch.conf.js

    selenium: {
        start_process: false,
        server_path: seleniumServer.path,
        host: 'jenkins',
        port: 4444
    },

Setting the flag start_process as false we are going to indicate the test must use the remote jenkins hub.

You can also run the project in you dev environment:

install all the npm packages using

npm install

run the test using

node nightwatch -e chrome

Pipeline

The pipeline build a docker image containing all the files needed to launch the test, run the container and after taht run the nightwatch test inside the container.

The container will be run using --network=host in order to let the container able to find the host name of the selenium hub.

FrancoMelandri / selenium-grid-tests