Selenium Docker

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Docker images for Selenium Standalone Server Hub and Node configurations with Chromium

Travis CI

Images included:

selenium/base: Base image which includes Java runtime and Selenium Server JAR file
selenium/hub: Image for running a Grid Hub
selenium/node-base: Base image for Grid Nodes which includes a virtual desktop environment
selenium/node-chromium: Grid Node with Chromium installed, needs to be connected to a Grid Hub
selenium/node-chromium-debug: Grid Node with Chromium installed and runs a VNC server, needs to be connected to a Grid Hub
selenium/standalone-chromium: Selenium Standalone with Chrome installed
selenium/standalone-chromium-debug: Selenium Standalone with Chromium installed and runs a VNC server

Running the images

❗ When executing docker run for an image with Chrome or Firefox please either mount -v /dev/shm:/dev/shm or use the flag --shm-size=2g to use the host's shared memory.

Chromium

$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm rbonghi/selenium-standalone-chromium:3.141.59-iron
#OR
$ docker run -d -p 4444:4444 --shm-size=2g rbonghi/selenium-standalone-chromium:3.141.59-iron

This is a known workaround to avoid the browser crashing inside a docker container, here are the documented issues for Chromium. 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.

Standalone Chromium

$ docker run -d -p 4444:4444 -v /dev/shm:/dev/shm rbonghi/selenium-standalone-chromium:3.141.59-iron

Note: Only one standalone image can run on port 4444 at a time.

To inspect visually what the browser is doing use the standalone-chromium-debug image. See Debugging section for details.

Selenium Grid Hub and Nodes

There are different ways to run the images and create a grid, check the following options.

Using docker networking

With this option, 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 4444:4444 --net grid --name selenium-hub rbonghi/selenium-hub:3.141.59-iron
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm rbonghi/selenium-node-chromium:3.141.59-iron

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

# Remove all unused networks
$ docker network prune
# OR
# Removes the grid network
$ docker network rm grid

Via docker-compose

The most simple way to start a grid is with docker-compose, use the following snippet as your docker-compose.yaml, save it locally and in the same folder run docker-compose up.

Version 2

# To execute this docker-compose yml file use `docker-compose -f <file_name> up`
# Add the `-d` flag at the end for detached execution
version: '2'
services:
  chromium:
    image: rbonghi/selenium-node-chromium:3.141.59-iron
    volumes:
      - /dev/shm:/dev/shm
    depends_on:
      - hub
    environment:
      HUB_HOST: hub

  hub:
    image: rbonghi/selenium-hub:3.141.59-iron
    ports:
      - "4444:4444"

Version 3

# To execute this docker-compose yml file use `docker-compose -f <file_name> up`
# Add the `-d` flag at the end for detached execution
version: "3"
services:
  selenium-hub:
    image: rbonghi/selenium-hub:3.141.59-iron
    container_name: selenium-hub
    ports:
      - "4444:4444"
  chromium:
    image: rbonghi/selenium-node-chromium:3.141.59-iron
    volumes:
      - /dev/shm:/dev/shm
    depends_on:
      - selenium-hub
    environment:
      - HUB_HOST=selenium-hub
      - HUB_PORT=4444

To stop the grid and cleanup the created containers, run docker-compose down.

Version 3 with Swarm support

# To start Docker in Swarm mode, you need to run `docker swarm init`
# To deploy the Grid, `docker stack deploy -c docker-compose.yml grid`
# Stop with `docker stack rm grid`

version: '3.7'

services:
  hub:
   image: selenium/hub:3.141.59-iron
   ports:
     - "4444:4444"

  chromium:
    image: rbonghi/selenium-node-chromium:3.141.59-iron
    volumes:
      - /dev/shm:/dev/shm
    environment:
      HUB_HOST: hub
      HUB_PORT: 4444
    deploy:
        replicas: 1
    entrypoint: bash -c 'SE_OPTS="-host $$HOSTNAME" /opt/bin/entry_point.sh'

Using `--link`

This option can be used for a single host scenario (hub and nodes running in a single machine), but it is not recommended for longer term usage since this is a docker legacy feature. It could serve you as an option for a proof of concept, and for simplicity it is used in the examples shown from now on.

$ docker run -d -p 4444:4444 --name selenium-hub rbonghi/selenium-hub:3.141.59-iron
$ docker run -d --link selenium-hub:hub -v /dev/shm:/dev/shm rbonghi/selenium-node-chromium:3.141.59-iron

Deploying to Kubernetes

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

Configuring the containers

JAVA_OPTS Java Environment Options

You can pass JAVA_OPTS environment variable to java process.

$ docker run -d -p 4444:4444 -e JAVA_OPTS=-Xmx512m --name selenium-hub rbonghi/selenium-hub:3.141.59-iron

SE_OPTS Selenium Configuration Options

You can pass SE_OPTS variable with additional commandline parameters for starting a hub or a node.

$ docker run -d -p 4444:4444 -e SE_OPTS="-debug" --name selenium-hub rbonghi/selenium-hub:3.141.59-iron

Selenium Hub and Node Configuration options

For special network configurations or when the hub and the nodes are running on different machines HUB_HOST and HUB_PORT or REMOTE_HOST can be used.

You can pass the HUB_HOST and HUB_PORT options to provide the hub address to a node when needed.

# Assuming a hub was already started on the default port
$ docker run -d -e HUB_HOST=<hub_ip|hub_name> -e HUB_PORT=4444 rbonghi/selenium-node-chromium:3.141.59-iron

Some network topologies might prevent the hub to reach the node through the url given at registration time, REMOTE_HOST can be used to supply the hub a url where the node is reachable under your specific network configuration

# Assuming a hub was already started on the default port
$ docker run -d -p <node_port>:5555 -e HUB_HOST=<hub_ip|hub_name> -e HUB_PORT=4444 -e REMOTE_HOST="http://<node_ip|node_name>:<node_port>" rbonghi/selenium-node-chromium:3.141.59-iron

Setting Screen Resolution

By default, nodes start with a screen resolution of 1360 x 1020 with a color depth of 24 bits. These settings can be adjusted by specifying SCREEN_WIDTH, SCREEN_HEIGHT and/or SCREEN_DEPTH environmental variables when starting the container.

docker run -d -e SCREEN_WIDTH=1366 -e SCREEN_HEIGHT=768 -e SCREEN_DEPTH=24 rbonghi/selenium-standalone-chromium

Increasing the number of browser instances/slots

By default, each image will only allow one slot per container, which is what we recommend as a best practice since all container resources and variables will be used for that browser, and this helps to have more stable tests.

Nevertheless, if you would like to have more slots per node, this can be configured via environment variables with the environment variable NODE_MAX_INSTANCES. For example, a Firefox node with 5 slots:

# Assuming a hub was already started
$ docker run -d -e HUB_HOST=<hub_ip|hub_name> -e NODE_MAX_INSTANCES=5 rbonghi/selenium-node-chromium:3.141.59-iron

Don't forget to combine this with the environment variable NODE_MAX_SESSION, which sets the maximum amount of tests that can run at the same time in a node. Following the previous example, if NODE_MAX_INSTANCES=5, then NODE_MAX_SESSION should also be at least 5. Full example:

# Assuming a hub was already started
$ docker run -d -e HUB_HOST=<hub_ip|hub_name> -e NODE_MAX_INSTANCES=5 -e NODE_MAX_SESSION=5 rbonghi/selenium-node-chromium:3.141.59-iron

Running in Headless mode

Both Firefox and Chrome support running tests in 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 environment variable to false (or any other value than true), for example:

$ docker run -d --net grid -e HUB_HOST=selenium-hub -e START_XVFB=false -v /dev/shm:/dev/shm rbonghi/selenium-node-chromium

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

$ 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 current version number thus overwriting the images downloaded from Docker Hub.

Using the images

Example: Spawn a container for testing in Chromium:

$ docker run -d --name selenium-hub -p 4444:4444 selenium/hub:3.141.59-iron
$ CH=$(docker run --rm --name=ch \
    --link selenium-hub:hub -v /e2e/uploads:/e2e/uploads \
    -v /dev/shm:/dev/shm \
    selenium/node-chromium:3.141.59-iron)

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.

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 a node, could look like this:

{
  "status": 0,
  "value": {
    "ready": true,
    "message": "Hub has capacity",
    "build": {
      "revision": "aacccce0",
      "time": "2018-08-02T20:13:22.693Z",
      "version": "3.14.0"
    },
    "os": {
      "arch": "amd64",
      "name": "Linux",
      "version": "4.9.93-linuxkit-aufs"
    },
    "java": {
      "version": "1.8.0_181"
    }
  }
}

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 when the docker container is started.

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 and --port parameters for the ones used in your environment.

$ 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 \
    rbonghi/selenium-hub:3.141.59-iron
$ docker run -d --net grid -e HUB_HOST=selenium-hub -v /dev/shm:/dev/shm rbonghi/selenium-node-chromium:3.141.59-iron

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:

$ 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="$@"

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

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:

$ ./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 visually see what the browser is doing you will want to run the debug variant of node or standalone images. A VNC server will run on port 5900. You are free to map that to any free external port that you wish. Keep in mind that you will only be able to run one node per port so if you wish to include a second node, or more, you will have to use different ports, the 5900 as the internal port will have to remain the same though as thats the VNC service on the node. The second example below shows how to run multiple nodes and with different VNC ports open:

$ docker run -d -P -p <port4VNC>:5900 --link selenium-hub:hub -v /dev/shm:/dev/shm rbonghi/selenium-node-chromium-debug:3.141.59-iron

e.g.:

$ docker run -d -P -p 5900:5900 --link selenium-hub:hub -v /dev/shm:/dev/shm rbonghi/selenium-node-chromium-debug:3.141.59-iron

to connect to the Chrome node on 5900 and the Firefox node on 5901 (assuming those node are free, and reachable).

And for standalone:

$ docker run -d -p 4444:4444 -p <port4VNC>:5900 -v /dev/shm:/dev/shm rbonghi/selenium-standalone-chromium-debug:3.141.59-iron

or

$ docker run -d -p 4444:4444 -p 5900:5900 -v /dev/shm:/dev/shm rbonghi/selenium-standalone-chromium-debug:3.141.59-iron

You can acquire the port that the VNC server is exposed to by running: (Assuming that we mapped the ports like this: 49338:5900)

$ docker port <container-name|container-id> 5900
#=> 0.0.0.0:49338

In case you have RealVNC binary vnc in your path, you can always take a look, view only to avoid messing around your tests with an unintended mouse click or keyboard interrupt:

$ ./bin/vncview 127.0.0.1:49160

If you are running Boot2Docker on OS X then you already have a VNC client built-in. You can connect by entering vnc://<boot2docker-ip>:49160 in Safari or Alfred.

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:

#FROM selenium/node-chromium-debug:3.141.59-iron
#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 is sent to stdout so it can be inspected by running:

$ 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 or Chrome (respectively) in headless mode.

License

rbonghi/docker-selenium

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