The most obvious solution is to get a workflow post-function to do it. And since post-functions that come available out of the box are very limited in their functionality, I would recommend using an addon, to expand available options. Either Scriptrunner or JMWE.
JIRA does not have a native functionality to close a sub task once the parent issue is closed.
In your case you will need an add-on to do that (like the JIRA ScriptRunner).
If your JIRA has the ScriptRunner plugin then you can have a look on how to achieve it at auto close all subtasks.
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
We're bringing product updates and pro tips on teamwork to ten cities around the world.Save your spot