Install and Run Selenium in Docker

1. Overview

In today’s fast-paced world, automation testing has become a crucial part of the software development process. Selenium is a popular tool used for automated testing of Web applications. Docker, on the other hand, is a platform that enables developers to easily pack, ship, and run applications in containers. Thus, installing and running Selenium in Docker enables us to harness the capabilities of two powerful technologies to perform efficient testing. However, the process of doing so may prove to be a bit tricky.

In this tutorial, we’ll have a detailed discussion on the step-by-step process of installing and running Selenium in Docker.

Notably, all the commands in this tutorial have been tested on Ubuntu 22.04.

2. Setting Up Docker

As usual, the first step in the process is to ensure Docker is available on the system.

2.1. Installing Required Dependencies

To start with, let’s use the apt command to update the package list on the machine:

$ sudo apt update

Now, we install the packages that Docker requires:

$ sudo apt install apt-transport-https ca-certificates curl software-properties-common

Doing so ensures that Docker functions smoothly on our device.

2.2. Adding the Docker Repository to the System

The next thing to do is to add the Docker repository to the system.

For this, we just use the curl command to add the GPG key that corresponds to the official Docker repository to the system:

$ curl -fsL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

Here, we used three options:

• -f (–fail): fail silently, i.e., not provide an output on server errors
• -s (–silent): perform a silent or quiet installation
• -L (–location): if the requested webpage is moved to a new location, this option makes curl resend the request to the new location

After that, let’s use the add-apt-repository command to add the Docker repository to the system:

$ sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

Let’s now proceed to the final step.

2.3. Installing Docker

The final step is to install Docker on the system:

$ sudo apt install docker-ce

Once the installation is complete, let’s use the systemctl command to start Docker on the machine:

$ sudo systemctl start docker

Finally, we verify that Docker is running on the system:

$ sudo systemctl status docker
 * Docker is running

As we can see above, Docker is indeed running on the machine.

In the next section, let’s learn how to set up Selenium in Docker.

3. Setting Up Selenium in Docker

When it comes to the Selenium deployment, there are a couple of steps we go through.

3.1. Pulling a Docker Image

We have to use a docker image to set up Selenium in Docker. There are several Docker images available on the Internet. For this tutorial, we use the selenium/standalone-chrome docker image. This image enables us to launch Selenium in the Chrome browser, helping us run Selenium tests remotely.

With that said, we should also make sure that Chrome exists on the machine.

Next, let’s use the docker pull command to pull the selenium/standalone-chrome Docker image:

$ sudo docker pull selenium/standalone-chrome

After that, we verify the successful operation via the docker images command:

$ sudo docker images
REPOSITORY                   TAG       IMAGE ID       CREATED       SIZE
selenium/standalone-chrome   latest    66d3196083ca   2 weeks ago   1.44GB

Evidently, we’ve successfully pulled the image to the machine.

3.2. Starting a Docker Container

The next thing to do is to start a Docker container from the pulled image. Let’s do so using the docker run command:

$ sudo docker run -d -p 4444:4444 selenium/standalone-chrome
6785a23708bf8274115505d5401995624e0385a35d3cc4bd7367f66d50193712

Above, we use a couple of options:

• -d, short for –detach, runs the container in detached or background mode
• -p, short for –publish, links the host port 4444 to the container port 4444

Thus, we can launch and access Selenium at https://localhost:4444.

Moreover, the container ID from the terminal indicates that the container started successfully.

So, let’s now navigate to https://localhost:4444 in Chrome to access Selenium:

The above image indicates that we’ve successfully finished setting up Selenium in Docker.

Next, we’ll run a Selenium test in Docker to verify that everything is working correctly.

4. Running a Selenium Test in Docker

There are several languages that we can use to write Selenium tests, such as Java, Python, and more. For this tutorial, we go with Python.

The first step in this process is to create a Python script for writing the test. So, let’s create a file named test.py:

$ touch test.py

Then, we write a simple test in the newly created file:

$ cat test.py
# Import Selenium WebDriver
from selenium import webdriver

# Initialize a new Chrome instance
browser = webdriver.Remote("http://localhost:4444", options=webdriver.ChromeOptions())

# Visit the Baeldung website
browser.get("https://baeldung.com")

# Print the title of the homepage
print(browser.title)

browser.quit()

After inserting the above test, let’s save and close the file.

Next, let’s run the test:

$ python test.py
Baeldung

As we can see above, the title of the Baeldung homepage is printed on the terminal.

Furthermore, we can navigate to the Sessions tab at https://localhost:4444/ during the test:

Thus, we see the currently active test session.

5. Conclusion

In this article, we learned how to install Docker, how to set up Selenium in Docker, and how to run a simple Selenium test in Docker.

By following this step-by-step guide, we should have Selenium running in Docker on the system in no time ready to use for automated web testing.