Docker images for the Selenium Grid Server

The project is made possible by volunteer contributors who have put in thousands of hours of their own time, and made the source code freely available under the Apache License 2.0.

:point_right: Status: Grid 4 is under development and on a Alpha stage

We are doing prereleases on a regular basis to get early feedback. This means that all other Selenium components can be currently at a different alpha version (e.g. bindings on Alpha 6, and these Docker images on prerelease Alpha 7).

Docker images for Grid 4 come with a handful of tags to simplify its usage, have a look at them in one of our prereleases

To get notifications of new prereleases, add yourself as a watcher of "Releases only".

Doubts or questions? Please get in touch through the different communication channels available in the Community section.

Looking for Grid 3? Head to the Selenium 3 branch. This branch will be having new browser releases until Grid 4 has its major release.

Community

Do you need help to use these Docker images? All the contact points for the different Selenium projects can be seen at: https://www.selenium.dev/support/

Quick start

1. Start a Docker container with Firefox

$ docker run -d -p 4444:4444 --shm-size 2g selenium/standalone-firefox:4.0.0-alpha-7-prerelease-20201009
# OR
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-firefox:4.0.0-alpha-7-prerelease-20201009

1. Point your WebDriver tests to http://localhost:4444/wd/hub

2. That's it!

To inspect visually the browser activity, see the Debugging section for details.

:point_up: When executing

docker run

-v /dev/shm:/dev/shm

--shm-size=2g

Why is

-v /dev/shm:/dev/shm

or

--shm-size 2g

necessary? This is a known workaround to avoid the browser crashing inside a docker container, here are the documented issues for Chrome and Firefox. The shm size of 2gb is arbitrary but known to work well, your specific use case might need a different value, it is recommended to tune this value according to your needs. Along the examples

-v /dev/shm:/dev/shm

will be used, but both are known to work.

:point_up: Always use a tag with an element suffix to pin a specific browser version. See Tagging Conventions for details.

Standalone

Firefox

bash
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-firefox:4.0.0-alpha-7-prerelease-20201009

Chrome

bash
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-chrome:4.0.0-alpha-7-prerelease-20201009

Opera

bash
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-opera:4.0.0-alpha-7-prerelease-20201009

Note: Only one Standalone container can run on port

4444

Selenium Grid Hub and Nodes

There are different ways to run the images and create a Grid with a Hub and Nodes, check the following options.

Docker networking

The Hub and Nodes will be created in the same network and they will recognize each other by their container name. A Docker network needs to be created as a first step.

$ docker network create grid
$ docker run -d -p 4442-4444:4442-4444 --net grid --name selenium-hub selenium/hub:4.0.0-alpha-7-prerelease-20201009
$ docker run -d --net grid -e SE_EVENT_BUS_HOST=selenium-hub \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
    -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -v /dev/shm:/dev/shm \
    selenium/node-chrome:4.0.0-alpha-7-prerelease-20201009
$ docker run -d --net grid -e SE_EVENT_BUS_HOST=selenium-hub \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
    -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -v /dev/shm:/dev/shm selenium/node-firefox:4.0.0-alpha-7-prerelease-20201009
$ docker run -d --net grid -e SE_EVENT_BUS_HOST=selenium-hub \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
    -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -v /dev/shm:/dev/shm selenium/node-opera:4.0.0-alpha-7-prerelease-20201009

When you are done using the Grid, and the containers have exited, the network can be removed with the following command:

# Removes the grid network
$ docker network rm grid

Docker Compose

Docker Compose is the simplest way to start a Grid. Use the linked resources below, save them locally, and check the execution instructions on top of each file.

Version 2

docker-compose-v2.yml

Version 3

docker-compose-v3.yml

To stop the Grid and cleanup the created containers, run

docker-compose down

Version 3 with Swarm support

docker-compose-v3-swarm.yml

Selenium Grid - Router, Distributor, EventBus, SessionMap and Nodes

It is possible to start a Selenium Grid with its five components apart. For simplicity, only an example with docker-compose will be provided. Save the file locally, and check the execution instructions on top of it.

docker-compose-v3-full-grid.yml

Dynamic Grid

Grid 4 has the ability to start Docker containers on demand, this means that it starts a Docker container in the background for each new session request, the test gets executed there, and when the test completes, the container gets thrown away.

This execution mode can be used either in the Standalone or Node roles. The "dynamic" execution mode needs to be told what Docker images to use when the containers get started. Additionally, the Grid needs to know the URI of the Docker daemon.

Configuration example

You can save this file locally and name it, for example,

config.toml

Configs have a mapping between the Docker image to use and the capabilities that need to be matched to

start a container with the given image.

configs = [ "selenium/standalone-firefox:4.0.0-alpha-7-prerelease-20201009", "{\"browserName\": \"firefox\"}", "selenium/standalone-chrome:4.0.0-alpha-7-prerelease-20201009", "{\"browserName\": \"chrome\"}", "selenium/standalone-opera:4.0.0-alpha-7-prerelease-20201009", "{\"browserName\": \"operablink\"}" ]

URL for connecting to the docker daemon

host.docker.internal works for macOS and Windows.

Linux could use --net=host in the

docker run

instruction or 172.17.0.1 in the URI below.

To have Docker listening through tcp on macOS, install socat and run the following command

socat -4 TCP-LISTEN:2375,fork UNIX-CONNECT:/var/run/docker.sock

host = "tcp://host.docker.internal:2375" ```

Execution with Hub & Node roles

This can be expanded to a full Grid deployment, all components deployed individually. The overall idea is to have the Hub in one virtual machine, and each of the Nodes in separate and more powerful virtual machines.

$ docker network create grid
$ docker run -d -p 4442-4444:4442-4444 --net grid --name selenium-hub selenium/hub:4.0.0-alpha-7-20201009
$ docker run -d --net grid -e SE_EVENT_BUS_HOST=selenium-hub \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
    -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -v ${PWD}/config.toml:/opt/bin/config.toml \
    selenium/node-docker:4.0.0-alpha-7-20201009

When you are done using the Grid, and the containers have exited, the network can be removed with the following command:

# Removes the grid network
$ docker network rm grid

Execution with Standalone roles

docker run --rm -ti --name selenium-docker -p 4444:4444 \
    -v ${PWD}/config.toml:/opt/bin/config.toml \
    selenium/standalone-docker:4.0.0-alpha-7-20201009

Video recording

It is possible to record your tests running in containers by using the

selenium/video:ffmpeg-4.3.1-20201009

Currently, the only way to do this mapping is manually (either starting the containers manually, or through

docker-compose

The video Docker image we provide is based on the ffmpeg Ubuntu image provided by the jrottenberg/ffmpeg project, thank you for providing this image and simplifying our work :tada:

Notes: - If you have questions or feedback, please use the community contact points shown here. - Please report any bugs through GitHub issues, and provide all the information requested on the template. - Video recording for headless browsers is not supported. - Video recording tends to use considerable amounts of CPU. Normally you should estimate 1CPU per video container, and 1 CPU per browser container. - Videos are stored in the

/videos

FILE_NAME

This example shows how to start the containers manually:

$ docker network create grid
$ docker run -d -p 4444:4444 -p 6900:5900 --net grid --name selenium -v /dev/shm:/dev/shm selenium/standalone-chrome:4.0.0-alpha-7-20201009
$ docker run -d --net grid --name video -v /tmp/videos:/videos selenium/video:ffmpeg-4.3.1-20201009
# Run your tests
$ docker stop video && docker rm video
$ docker stop selenium && docker rm selenium

After the containers are stopped and removed, you should see a video file on your machine's

/tmp/videos

Here is an example using a Hub and 3 Nodes (Chrome, Firefox, and Opera):

docker-compose-v3-video.yml

Deploying to Kubernetes

Here are the steps to deploy the Grid 4 to a Kubernetes cluster. ``` bash

Deploying all the grid components to kubernetes

$ kubectl apply -f k8s-deployment-full-grid.yaml

Exposing the router

$ kubectl expose deployment selenium-router-deployment --type=NodePort --port=4444

Get the router URL to access the grid from outside K8s cluster

$ minikube service selenium-router-deployment --url

To list all the Grid componenets

$ kubectl get all -l component=selenium-grid-4 ```

Check out the Kubernetes examples on how to deploy selenium hub and nodes on a Kubernetes cluster.

Configuring the containers

SE_OPTS Selenium Configuration Options

You can pass

SE_OPTS

$ docker run -d -p 4444:4444 -e SE_OPTS="-debug" --name selenium-hub selenium/hub:4.0.0-alpha-7-prerelease-20201009

JAVA_OPTS Java Environment Options

You can pass

JAVA_OPTS

$ docker run -d -p 4444:4444 -e JAVA_OPTS=-Xmx512m --name selenium-hub selenium/hub:4.0.0-alpha-7-prerelease-20201009

Node configuration options

The Nodes register themselves through the Event Bus. When the Grid is started in its typical Hub/Node setup, the Hub will be the one acting as the Event Bus, and when the Grid is started with all its five elements apart, the Event Bus will be running on its own.

In both cases, it is necessary to tell the Node where the Event Bus is, so it can register itself. That is the purpose of the

SE_EVENT_BUS_HOST

SE_EVENT_BUS_PUBLISH_PORT

SE_EVENT_BUS_SUBSCRIBE_PORT

Here is an example with the default values of these environment variables:

$ docker run -d --e SE_EVENT_BUS_HOST= -e SE_EVENT_BUS_PUBLISH_PORT=4442 -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 -v /dev/shm:/dev/shm selenium/node-chrome:4.0.0-alpha-7-prerelease-20201009

Setting Screen Resolution

By default, nodes start with a screen resolution of 1360 x 1020 with a color depth of 24 bits and a dpi of 96. These settings can be adjusted by specifying

SCREEN_WIDTH

SCREEN_HEIGHT

SCREEN_DEPTH

SCREEN_DPI

docker run -d -e SCREEN_WIDTH=1366 -e SCREEN_HEIGHT=768 -e SCREEN_DEPTH=24 -e SCREEN_DPI=74 selenium/standalone-firefox

Running in Headless mode

Firefox, Chrome and Opera support running tests in the headless mode. When using headless mode, there's no need for the Xvfb server to be started.

To avoid starting the server you can set the

START_XVFB

false

true

$ docker run -d --net grid -e SE_EVENT_BUS_HOST=selenium-hub -e SE_EVENT_BUS_PUBLISH_PORT=4442 -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 -e START_XVFB=false -v /dev/shm:/dev/shm selenium/node-chrome

For more information, see this GitHub issue.

Building the images

Clone the repo and from the project directory root you can build everything by running:

$ VERSION=local make build

If you need to configure environment variable in order to build the image (http proxy for instance), simply set an environment variable

BUILD_ARGS

$ BUILD_ARGS="--build-arg http_proxy=http://acme:3128 --build-arg https_proxy=http://acme:3128" make build

Note: Omitting

VERSION=local

Using the images

Example: Spawn a container for testing in Firefox

$ docker network create grid
$ docker run -d -p 4442-4444:4442-4444 --net grid --name selenium-hub selenium/hub:4.0.0-alpha-7-prerelease-20201009
$ docker run -d --net grid -e SE_EVENT_BUS_HOST=selenium-hub \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -v /dev/shm:/dev/shm \
    -v /e2e/uploads:/e2e/uploads selenium/node-firefox:4.0.0-alpha-7-prerelease-20201009

Note:

-v /e2e/uploads:/e2e/uploads

This command line for Opera or Chrome is almost the same, only remember to replace the image name for

node-opera

node-chrome

:focus

Note: Since a Docker container should not preserve state and spawning a new one takes less than 3 seconds you will likely want to remove containers after each end-to-end test with

--rm

Waiting for the Grid to be ready

It is a good practice to check first if the Grid is up and ready to receive requests, this can be done by checking the

/wd/hub/status

A Grid that is ready, composed by a hub and two nodes, could look like this:

{
  "value": {
    "ready": true,
    "message": "Selenium Grid ready.",
    "nodes": [
      {
        "id": "6c0a2c59-7e99-469d-bbfc-313dc638797c",
        "uri": "http:\u002f\u002f172.19.0.3:5555",
        "maxSessions": 4,
        "stereotypes": [
          {
            "capabilities": {
              "browserName": "firefox"
            },
            "count": 4
          }
        ],
        "sessions": [
        ]
      },
      {
        "id": "26af3363-a0d8-4bd6-a854-2c7497ed64a4",
        "uri": "http:\u002f\u002f172.19.0.4:5555",
        "maxSessions": 4,
        "stereotypes": [
          {
            "capabilities": {
              "browserName": "chrome"
            },
            "count": 4
          }
        ],
        "sessions": [
        ]
      }
    ]
  }
}

The

"ready": true

Adding a HEALTHCHECK to the Grid

The script check-grid.sh, which is included in the images, can be used to poll the Grid status.

This example checks the status of the Grid every 15 seconds, it has a timeout of 30 seconds when the check is done, and it retries up to 5 times until the container is marked as unhealthy. Please use adjusted values to fit your needs, (if needed) replace the

--host

--port

$ docker network create grid
$ docker run -d -p 4444:4444 --net grid --name selenium-hub \
    --health-cmd='/opt/bin/check-grid.sh --host 0.0.0.0 --port 4444' \
    --health-interval=15s --health-timeout=30s --health-retries=5 \
    selenium/hub:4.0.0-alpha-7-prerelease-20201009
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm selenium/node-chrome:4.0.0-alpha-7-prerelease-20201009
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm selenium/node-firefox:4.0.0-alpha-7-prerelease-20201009
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm selenium/node-opera:4.0.0-alpha-7-prerelease-20201009

Note: The

\

^

The container health status can be checked by doing

docker ps

(healthy)|(unhealthy)

$ docker inspect --format='{{json .State.Health.Status}}' selenium-hub
"healthy"

Using a bash script to wait for the Grid

A common problem known in docker is that a running container does not always mean that the application inside it is ready. A simple way to tackle this is by using a "wait-for-it" script, more information can be seen here.

The following script is an example of how this can be done using bash, but the same principle applies if you want to do this with the programming language used to write the tests.

#!/bin/bash
# wait-for-grid.sh

set -e
cmd="[email protected]"
while ! curl -sSL "http://localhost:4444/wd/hub/status" 2>&1 
        | jq -r '.value.ready' 2>&1 | grep "true" >/dev/null; do
    echo 'Waiting for the Grid'
    sleep 1
done
>&2 echo "Selenium Grid is up - executing tests"
exec $cmd

Will require

jq

installed via

apt-get

, else the script will keep printing

Waiting

without completing the execution.

Note: If needed, replace

localhost

4444

Let's say that the normal command to execute your tests is

mvn clean test

$ ./wait-for-grid.sh mvn clean test

Like this, the script will poll until the Grid is ready, and then your tests will start.

Debugging

In the event you wish to see what the browser is doing, you can check what is going inside by connecting to the VNC server running on port 5900 inside the browser container.

You are free to map that port to any free external port that you wish. Keep in mind that you will only be able to run one node per port. If you wish to include a second node (or more), you will have to use different ports.

The internal 5900 port will need to remain the same because that is the configured port for the VNC server running inside the container.

Here is an example with the standalone images, the same concept applies to the node images.

bash
$ docker run -d -p 4444:4444 -p 5900:5900 -v /dev/shm:/dev/shm selenium/standalone-chrome:4.0.0-alpha-7-prerelease-20201009
$ docker run -d -p 4445:4444 -p 5901:5900 -v /dev/shm:/dev/shm selenium/standalone-firefox:4.0.0-alpha-7-prerelease-20201009
$ docker run -d -p 4446:4444 -p 5902:5900 -v /dev/shm:/dev/shm selenium/standalone-opera:4.0.0-alpha-7-prerelease-20201009

Then, you would use in your VNC client: - Port 5900 to connect to the Chrome container - Port 5901 to connect to the Firefox container - Port 5902 to connect to the Opera container

In case you have RealVNC binary

vnc

bash
$ ./bin/vncview 127.0.0.1:5900

When you are prompted for the password it is

secret

/NodeBase/Dockerfile

FROM selenium/node-chrome:4.0.0-alpha-7-prerelease-20201009

FROM selenium/node-firefox:4.0.0-alpha-7-prerelease-20201009

FROM selenium/node-opera:4.0.0-alpha-7-prerelease-20201009

Choose the FROM statement that works for you.

RUN x11vnc -storepasswd /home/seluser/.vnc/passwd ```

If you want to run VNC without password authentication you can set the environment variable

VNC_NO_PASSWORD=1

Troubleshooting

All output gets sent to stdout, so it can be inspected by running:

bash
$ docker logs -f 

You can turn on debugging by passing environment variable to the hub and the nodes containers:

GRID_DEBUG=true

Headless

If you see the following selenium exceptions:

Message: invalid argument: can't kill an exited process

or

Message: unknown error: Chrome failed to start: exited abnormally

The reason might be that you've set the

START_XVFB