NiFi is comprised of a number of web applications (web UI, web API, documentation, custom UIs, data viewers, etc)
Is it possible to install only specific app ?
There are no easy way to do it, everythings is in the same JVM.
However nifi is open source, feel free to modify it for your requirement : https://github.com/apache/nifi
do you take a look at minifi project : https://nifi.apache.org/minifi/index.html ?