# docker-selenium

**Repository Path**: better319/docker-selenium

## Basic Information

- **Project Name**: docker-selenium
- **Description**: Docker images for the Selenium Grid Server
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: trunk
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 3
- **Created**: 2021-01-04
- **Last Updated**: 2022-04-19

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# 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](LICENSE.md).

![Build & test](https://github.com/SeleniumHQ/docker-selenium/workflows/Build%20&%20test/badge.svg?branch=trunk)
![Deployments](https://github.com/SeleniumHQ/docker-selenium/workflows/Deploys/badge.svg)

# :point_right: Status: Grid 4 is under development and on a [Alpha stage](https://en.wikipedia.org/wiki/Software_release_life_cycle#Alpha)
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 7, and Docker images on prerelease Beta 1).

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](https://github.com/SeleniumHQ/docker-selenium/releases/tag/4.0.0-beta-1-prerelease-20201208)

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](https://github.com/SeleniumHQ/docker-selenium/tree/selenium-3). 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

``` bash
$ docker run -d -p 4444:4444 --shm-size 2g selenium/standalone-firefox:4.0.0-beta-1-prerelease-20201208
# OR
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-firefox:4.0.0-beta-1-prerelease-20201208
```

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

3. That's it! 

To inspect visually the browser activity, see the [Debugging](#debugging) section for details.

:point_up: When executing `docker run` for an image that contains a browser please either mount 
  `-v /dev/shm:/dev/shm` or use the flag `--shm-size=2g` to use the host's shared memory.
  
> 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](https://code.google.com/p/chromium/issues/detail?id=519952) and [Firefox](https://bugzilla.mozilla.org/show_bug.cgi?id=1338771#c10).
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 Docker image with a full tag to pin a specific browser and Grid version.
See [Tagging Conventions](https://github.com/SeleniumHQ/docker-selenium/wiki/Tagging-Convention) for details.

___

## Standalone

![Firefox](https://raw.githubusercontent.com/alrra/browser-logos/main/src/firefox/firefox_24x24.png) Firefox 
``` bash
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-firefox:4.0.0-beta-1-prerelease-20201208
```

![Chrome](https://raw.githubusercontent.com/alrra/browser-logos/main/src/chrome/chrome_24x24.png) Chrome 
``` bash
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-chrome:4.0.0-beta-1-prerelease-20201208
```

![Opera](https://raw.githubusercontent.com/alrra/browser-logos/main/src/opera/opera_24x24.png) Opera 
``` bash
$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm selenium/standalone-opera:4.0.0-beta-1-prerelease-20201208
```

_Note: Only one Standalone container can run on port_ `4444` _at the same time._

___

## 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](https://docs.docker.com/engine/reference/commandline/network_create/) needs to be created as a first step.

``` bash
$ docker network create grid
$ docker run -d -p 4442-4444:4442-4444 --net grid --name selenium-hub selenium/hub:4.0.0-beta-1-prerelease-20201208
$ 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-beta-1-prerelease-20201208
$ 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-beta-1-prerelease-20201208
$ 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-beta-1-prerelease-20201208
```

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

``` bash
# Removes the grid network
$ docker network rm grid
```

### Using different machines/VMs
The Hub and Nodes will be created on different machines/VMs, they need to know each other's IPs to
communicate properly.

Hub - Machine/VM 1
``` bash
$ docker run -d -p 4442-4444:4442-4444 --name selenium-hub selenium/hub:4.0.0-beta-1-prerelease-20201208
```

Node Chrome - Machine/VM 2
``` bash
$ docker run -d -p 5555:5555 
    -e SE_EVENT_BUS_HOST=<ip-from-machine-1> \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
    -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -e SE_NODE_HOST=<ip-from-machine-2> \
    -v /dev/shm:/dev/shm \
    selenium/node-chrome:4.0.0-beta-1-prerelease-20201208
```

Node Firefox - Machine/VM 3
``` bash
$ docker run -d -p 5555:5555 
    -e SE_EVENT_BUS_HOST=<ip-from-machine-1> \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
    -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -e SE_NODE_HOST=<ip-from-machine-3> \
    -v /dev/shm:/dev/shm \
    selenium/node-firefox:4.0.0-beta-1-prerelease-20201208
```

Node Opera - Machine/VM 4
``` bash
$ docker run -d -p 5555:5555 
    -e SE_EVENT_BUS_HOST=<ip-from-machine-1> \
    -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
    -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
    -e SE_NODE_HOST=<ip-from-machine-4> \
    -v /dev/shm:/dev/shm \
    selenium/node-opera:4.0.0-beta-1-prerelease-20201208
```

### Docker Compose
[Docker Compose](https://docs.docker.com/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`](docker-compose-v2.yml)

#### Version 3
[`docker-compose-v3.yml`](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`](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`](docker-compose-v3-full-grid.yml)

___

## Video recording ![BETA](https://img.shields.io/badge/beta!-blue?style=for-the-badge)

It is possible to record your tests running in containers by using the `selenium/video:ffmpeg-4.3.1-20201208`
Docker image. One container is needed per each container where a browser is running. This means if you are
running 5 Nodes/Standalone containers, you will need 5 video containers, the mapping is 1-1.

Currently, the only way to do this mapping is manually (either starting the containers manually, or through
`docker-compose`). We are iterating on this process and probably this setup will be more simple in the future.

The video Docker image we provide is based on the ffmpeg Ubuntu image provided by the 
[jrottenberg/ffmpeg](https://github.com/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](https://www.selenium.dev/support/). 
- Please report any bugs through GitHub [issues](https://github.com/SeleniumHQ/docker-selenium/issues/new/choose), 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` directory inside the video container. Map a local directory to get the videos.
- If you are running more than one video container, be sure to overwrite the video file name through the `FILE_NAME`
environment variable to avoid unexpected results.

This example shows how to start the containers manually:

``` bash
$ 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-beta-1-prerelease-20201208
$ docker run -d --net grid --name video -v /tmp/videos:/videos selenium/video:ffmpeg-4.3.1-20201208
# 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` directory.

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

[`docker-compose-v3-video.yml`](docker-compose-v3-video.yml)

___

## Dynamic Grid ![BETA](https://img.shields.io/badge/beta!-blue?style=for-the-badge)

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`.
```toml
[docker]
# 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-beta-1-prerelease-20201208", "{\"browserName\": \"firefox\"}",
    "selenium/standalone-chrome:4.0.0-beta-1-prerelease-20201208", "{\"browserName\": \"chrome\"}",
    "selenium/standalone-opera:4.0.0-beta-1-prerelease-20201208", "{\"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"
# Docker imagee used for video recording
video-image = "selenium/video:ffmpeg-4.3.1-20201208"

# Uncomment the following section if you are running the node on a separate VM
# Fill out the placeholders with appropriate values
#[server]
#hostname = <ip-from-node-machine>
#port = <port-from-node-machine>
```

### 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. 

``` bash
$ docker network create grid
$ docker run -d -p 4442-4444:4442-4444 --net grid --name selenium-hub selenium/hub:4.0.0-beta-1-prerelease-20201208
$ 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 \
    -v /path/on/your/host/machine:/opt/selenium/assets \
    selenium/node-docker:4.0.0-beta-1-prerelease-20201208
```

To have the assets saved on your host, please mount your host path to `/opt/selenium/assets`.

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

``` bash
# Removes the grid network
$ docker network rm grid
```

### Execution with Standalone roles

```bash
docker run --rm -ti --name selenium-docker -p 4444:4444 \
    -v ${PWD}/config.toml:/opt/bin/config.toml \
    -v /path/on/your/host/machine:/opt/selenium/assets \
    selenium/standalone-docker:4.0.0-beta-1-prerelease-20201208
```

To have the assets saved on your host, please mount your host path to `/opt/selenium/assets`.

### Video recording, screen resolution, and time zones in a Dynamic Grid
To record your WebDriver session, you need to add a `se:options` section to
your capabilities and inside it, configure the desired settings, for example:

```json
{
  "browserName": "firefox",
  "platformName": "linux",
  "se:options": {
    "recordVideo": "true",
    "timeZone": "US/Pacific",
    "screenResolution": "1920x1080"
  }
}
```

After running a test, check the path you mounted to the Docker container, 
(`/path/on/your/host/machine`), and you should see videos and session information. 
___

## 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](https://github.com/kubernetes/examples/tree/master/staging/selenium)
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` variable with additional commandline parameters for starting a hub or a node.

``` bash
$ docker run -d -p 4444:4444 -e SE_OPTS="-debug" --name selenium-hub selenium/hub:4.0.0-beta-1-prerelease-20201208
```

### JAVA_OPTS Java Environment Options

You can pass `JAVA_OPTS` environment variable to java process.

``` bash
$ docker run -d -p 4444:4444 -e JAVA_OPTS=-Xmx512m --name selenium-hub selenium/hub:4.0.0-beta-1-prerelease-20201208
```

### 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` and `SE_EVENT_BUS_SUBSCRIBE_PORT` environment
variables.

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

```bash
$ docker run -d --e SE_EVENT_BUS_HOST=<event_bus_ip|event_bus_name> -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-beta-1-prerelease-20201208
```

### 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`, and/or `SCREEN_DPI` 
environmental variables when starting the container.

``` bash
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](https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Headless_mode), 
[Chrome](https://developers.google.com/web/updates/2017/04/headless-chrome) and 
[Opera](https://forums.opera.com/topic/20375/opera-cli-switches-and-headless) support running tests in the headless mode.
When using headless mode, there's no need for the [Xvfb](https://en.wikipedia.org/wiki/Xvfb) server to be started.

To avoid starting the server you can set the `START_XVFB` environment variable to `false` 
(or any other value than `true`), for example:

``` bash
$ 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](https://github.com/SeleniumHQ/docker-selenium/issues/567).
___

## Building the images

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

``` bash
$ 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` that contains the additional variables to pass to the 
docker context (this will only work with docker >= 1.9)

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

_Note: Omitting_ `VERSION=local` _will build the images with the released version but replacing the date for the 
current one._

## Using the images

### Example: Spawn a container for testing in Firefox ![Firefox](https://raw.githubusercontent.com/alrra/browser-logos/main/src/firefox/firefox_24x24.png)

``` bash
$ docker network create grid
$ docker run -d -p 4442-4444:4442-4444 --net grid --name selenium-hub selenium/hub:4.0.0-beta-1-prerelease-20201208
$ 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-beta-1-prerelease-20201208
```

_Note:_ `-v /e2e/uploads:/e2e/uploads` _is optional in case you are testing browser uploads on your 
web app you will probably need to share a directory for this._

This command line for Opera or Chrome is almost the same, only remember to replace the image name for 
`node-opera` or `node-chrome`. Remember that the Selenium running container is able to launch either 
Chrome, Opera or Firefox, the idea around having 3 separate containers, one for each browser is for convenience plus 
avoiding certain `:focus` issues your web app may encounter during end-to-end test automation.

_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` _command. You need to think of your 
Docker containers as single processes, not as running virtual machines._

___

## 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` endpoint.

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

```json
{
  "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` value indicates that the Grid is ready to receive requests. This status can be polled through a
script before running any test, or it can be added as a [HEALTHCHECK](https://docs.docker.com/engine/reference/run/#healthcheck)
when the docker container is started.

### Adding a [HEALTHCHECK](https://docs.docker.com/engine/reference/run/#healthcheck) to the Grid

The script [check-grid.sh](Base/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` and `--port` parameters for the ones used in your environment.

``` bash
$ 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-beta-1-prerelease-20201208
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm selenium/node-chrome:4.0.0-beta-1-prerelease-20201208
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm selenium/node-firefox:4.0.0-beta-1-prerelease-20201208
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm selenium/node-opera:4.0.0-beta-1-prerelease-20201208
```
**Note:** The `\` line delimiter won't work on Windows based terminals, try either `^` or a backtick.

The container health status can be checked by doing `docker ps` and verifying the `(healthy)|(unhealthy)` status or by
inspecting it in the following way:

```bash
$ 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](https://docs.docker.com/compose/startup-order/).

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.

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

set -e

cmd="$@"

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` and `4444` for the correct values in your environment. Also, this script is polling indefinitely, you might want
to tweak it and establish a timeout.

Let's say that the normal command to execute your tests is `mvn clean test`. Here is a way to use the above script and execute your tests:

```bash
$ ./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-beta-1-prerelease-20201208
$ docker run -d -p 4445:4444 -p 5901:5900 -v /dev/shm:/dev/shm selenium/standalone-firefox:4.0.0-beta-1-prerelease-20201208
$ docker run -d -p 4446:4444 -p 5902:5900 -v /dev/shm:/dev/shm selenium/standalone-opera:4.0.0-beta-1-prerelease-20201208
```

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](https://www.realvnc.com/) binary `vnc` in your path, you can always take a look, select view 
only to avoid messing around your tests with an unintended mouse click or keyboard interrupt:
``` bash
$ ./bin/vncview 127.0.0.1:5900
```

When you are prompted for the password it is `secret`. If you wish to change this then you should either change 
it in the `/NodeBase/Dockerfile` and build the images yourself, or you can define a Docker image that derives from 
the posted ones which reconfigures it:
``` dockerfile
#FROM selenium/node-chrome:4.0.0-beta-1-prerelease-20201208
#FROM selenium/node-firefox:4.0.0-beta-1-prerelease-20201208
#FROM selenium/node-opera:4.0.0-beta-1-prerelease-20201208
#Choose the FROM statement that works for you.

RUN x11vnc -storepasswd <your-password-here> /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 <container-id|container-name>
```

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` environment variable to "false", but forgot to 
actually run Firefox, Chrome or Opera in the headless mode.