Q:

Make liferay portlet non instanceable

How can I make my portlet non instanceable accross the liferay instance. I have read about it in the forum but there was no mention of how to do it.

A:

You can specify a portlet as non instanceable by putting
<liferay-portlet-app>
    ...
    <portlet>
        ...
        <instanceable>false</instanceable>
        ...
    </portlet>
    ...
</liferay-portlet-app>

in the file 
liferay-portlet.xml
Beware of the right order of tags, according to the dtd (linked the dtd version 5.2, shouldn't have changed much though)
Also have a look here
Liferay docu

