Prowlarr is part of the Servarr suite: it allows to manage a complex list of indexers for your other tools in a centralized and easy to add/edit/remove way,

You will need Prowlarr to add all your torrent trackers and Usenet indexers in one centralized place for all the others supported tools to use. Also, you can add download clients to Prowlarr and perform direct searches and grabs from within, which is neat too.

Prowlarr is easily installed and managed within Gentoo linux since there is an ebuild for it. All you need to do is unmask it (at the time of writing this it's are masked for AMD64 at least):

echo www-apps/prowlarr ~amd64 >> /etc/portage/package.accept_keywords/prowlarr

then install it:

emerge -v prowlarr

This step will create a dedicated prowlarr user but you will want to add it to the group media, that you have created before, so that the it will be able to access and manage your media collection:

usermod -a -G media prowlarr

Also, you want to move Prowlarr home folder under /data/daemons/prowlarr for consistency and to be protected on the RAID array, so:

usermod -m -d /data/daemons/prowlarr prowlarr

Before you proceed, you should make Prowlarr accessible via the reverse-proxy, so that access, configuration and usage will be simplified from the beginning. Add this file to /etc/nginx/folders:

prowlarr.conf

# Prowlarr - indexars
location /prowlarr {
        proxy_pass http://127.0.0.1:9696;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_redirect off;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $http_connection;
}
# Allow the API/Indexer External Access via NGINX
location ~ /prowlarr(/[0-9]+)?/api {
        auth_basic off;
        proxy_pass http://127.0.0.1:9696;
}

Refer to The Reverse Proxy concept on how to enable this configuration and restart the reverse proxy.

There are some configuration that must be perform before actually starting the service. You need to briefly start and stop it to let it create the main configuration file, this is required because you need o generate a new API key:

/etc/init.d/prowlarr start
/etc/init.d/prowlarr stop

Now edit the newly created xml config file /data/daemons/prowlarr/.config/Prowlarr and edit the UrlBase to match the reverse-proxy setup. Only change the following lines in the file, do not edit anything else (unless you know what you are doing):

  <UrlBase>prowlarr</UrlBase>
    <BindAddress>127.0.0.1</BindAddress>
  <AuthenticationMethod>Forms</AuthenticationMethod>
  <AuthenticationRequired>DisabledForLocalAddresses</AuthenticationRequired>

Add Prowlarr to default runlevel, for autostart on reboot, and start it manually now:

rc-update add prowlarr default
/etc/init.d/prowlarr start

Prowlarr will now be accessible as http://192.168.0.1/prowlarr.

All set! Prowlarr is running.

Head to the indexers page on the Web GUI and add your trackers / indexers. After you will have added the other services, you will need to go to the settings –> apps and add them one by one. To sync the indexers to the apps, use the sync all indexers button in the indexers page of Prowlarr.