Starting Activity through notification: Avoiding duplicate activities

Question

So I am currently showing a notification. When the user clicks this noticiation, the application is started. The notification persists, to indicate that the service is runni

Answer 1

That's the way it's supposed to be by default. You probably need to specify android:launchMode="singleTop" if you want to have a single instance only.
There are 4 launch modes, more info here: https://developer.android.com/guide/topics/manifest/activity-element.html