Note that 8.0 is the Python 3 release of Splunk. Whether you want to use Python 2 or 3, the order of operations and the appropriate versions of apps and add-ons are more rigid than usual. Full instructions for all upgrade scenarios with ITSI are covered here: Python 3 migration with ITSI.
Note the following:
- ITSI version 4.4.x is completely Python 2/3 compatible.
- Splunk Enterprise Security version 6.0 is compatible with Splunk Enterprise version 8.0, though it currently requires the Python 2 interpreter that ships with Splunk Enterprise 8.0.
Your upgrade path depends on whether or not you want to use Python 2 or Python 3. Regardless, because of the Python 3 migration changes, you MUST upgrade ITSI before you upgrade Splunk Enterprise, or else ITSI breaks.