Tutorial 30 – Docker Compose to create multiple docker containers
So far we have learnt how to create standalone selenium containers. The standalone container had both -> selenium grid (hub) and node.
We will now learn how to spin up multiple docker containers using docker compose and use it to start a grid.
Scroll down the official docker-selenium page https://github.com/SeleniumHQ/docker-selenium
You would see the docker compose section
The yaml (yet another markup language) file that you see above is a docker compose file. Using this file, we can create one or multiple docker containers.
Let us open the docker-compose-v3.yml
Notice that this file has 4 sections. The first 3 sections will help us in creating chrome/edge/firefox nodes (notice the respective images), the last section would create the hub container.
Also notice above that the 3 browsers ‘depends_on’ selenium-hub, which is quite understandable.
Create a new text file at any location and open the file in notepad or any other editor
Copy the .yml file contents from https://github.com/SeleniumHQ/docker-selenium/blob/trunk/docker-compose-v3.yml
Paste it in text file
Make sure that the contents of .yml are properly pasted in the above file otherwise you would get error later.
File > Save As (make sure the file name has .yml extension as shown below)
Notice below the file formatting changes and you can differentiate the different sections very clearly
Let us now start docker engine on windows by simply double clicking the docker desktop icon
Wait for the docker engine to start, you would see the docker dashboard icon once docker engine is ready
Click this docker dashboard icon, right now as you can see, no containers are running
Next cd to location where your .yml file is kept
Execute docker-compose up command. You will get below error because the filename that we have given is not supported. The error is suggesting us few filenames
Close the .yml file and rename the file to docker-compose.yml
Re-execute docker-compose up command. This time there shouldn’t be any error.
Notice below that the respective images are pulled from docker hub and the multiple containers are created
Launch http://localhost:4444
Notice below that the selenium hub is up and running. Moreover, 3 docker containers have been created. One container has firefox browser running, another container has edge, another has chrome)
Before we bring down the containers, Ctrl+C
To bring down the containers, execute docker-compose down
Notice below that the containers are no more running
To run containers in background, execute docker-compose up -d 
Refresh the session after sometime
The below command shows the 4 containers running
So this is how we can use docker compose to spin up multiple docker container sessions.
Before we wrap up, let us bring down the containers
Thank you for reading!
