[🐛 Bug]: No way to set maxInstances in Selenium Grid 4

[vinodkpasi]

What happened?

A clear and concise description of what the bug is.

In the previous grid version, we could specify maxInstances and instances like this:
browser browserName="chrome",platform=WINDOWS,maxInstances=1 -maxSession 1

With Selenium Grid 4, up to now, I have not found a way to modify to set the maxInstances

How can we reproduce the issue?

java -jar selenium-server-4.28.1.jar standalone

Relevant log output

No

Operating System

Windows 10

Selenium version

C#

What are the browser(s) and version(s) where you see this issue?

Chrome 133

What are the browser driver(s) and version(s) where you see this issue?

133

Are you using Selenium Grid?

4

[github-actions]

@vinodkpasi, thank you for creating this issue. We will troubleshoot it as soon as we can.

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Thank you!

[ivpel]

Hello @vinodkpasi ,

In Selenium 4, the maxInstances flag from Selenium 3 doesn’t work in standalone mode. If you only need a single session overall, you can do:
java -jar selenium-server-4.xx.jar standalone --max-sessions 1

But that limits all browsers to one session. To control concurrency per browser (e.g., one Chrome, multiple Firefox), you must switch to distributed mode (one process as Hub, separate processes as Nodes). There, you can use a configuration file (TOML, JSON, or YAML) specifying maxInstances for each browser. For example:

role = "node"
max-sessions = 5

[node]
port = 5555

[[node.driver]]
browserName = "chrome"
maxInstances = 1

[[node.driver]]
browserName = "firefox"
maxInstances = 3

Then start:

java -jar selenium-server-4.28.1.jar node --config node-config.toml

Here are details for configuration: https://www.selenium.dev/documentation/grid/configuration/toml_options/

[diemol]

Thank you for helping, @ivpel!

@vinodkpasi please see the reply above.

[github-actions]

This issue has been automatically locked since there has not been any recent activity since it was closed. Please open a new issue for related bugs.