I'm not at all familiar with Splunk, but one of my teams wants to integrate it with OpsGenie. I can see that there's the option on the OpsGenie side to create a Splunk integration, but they are looking at this support doc
and insisting that they need to install both the OpsGenie side integration and an app in Splunk. Admittedly the document is not clear on it; my thought is that you only need to install the app in Splunk if you want to be able to manually create an OpsGenie alert from within the Splunk UI.
Can someone clarify?