AutoNat qBittorrent

autonat.service

[Unit]
Description=AutoNat
After=multi-user.target

[Service]
Type=simple
ExecStart=/root/autonat.sh
Restart=always
RestartSec=5s
StartLimitIntervalSec=500
StartLimitBurst=5
[Install]
WantedBy=multi-user.target

autonat.sh

#!/usr/bin/env bash

QBITTORRENT="${GSP_QBT_ADDR:-http://localhost:${WEBUI_PORT:-8080}}"
QBT_COOKIES="--cookie-jar /tmp/cookies.txt --cookie /tmp/cookies.txt"
# Check and install qbittorrent
QBT_PORT=""

qbt_refresh_port() {
    QBT_PORT=$(curl --silent --fail --show-error ${CURL_OPT} ${QBT_COOKIES} "${QBITTORRENT}/api/v2/app/preferences" | jq ".listen_port" 2>/dev/null)
    echo "qBittorrent Listen Port is: ${QBT_PORT}"
}
qbt_refresh_port
while true ; do
    date
    gateway="10.2.0.1"
    mapping_info=$(natpmpc -a 1 0 tcp 60 -g $gateway)

    if [[ $mapping_info =~ Mapped\ public\ port\ ([0-9]+) ]]; then
        mapped_port="${BASH_REMATCH[1]}"
        echo "Mapped public port: $mapped_port"
        # Check if the mapped port has changed
        if [[ "$mapped_port" != "$QBT_PORT" ]]; then
            echo "Changing qBittorrent port to $mapped_port"

                # Change qBittorrent port
                curl \
                  --silent \
                  ${CURL_OPT} \
                  --request POST \
                  ${QBT_COOKIES} \
                  --url "${QBITTORRENT}/api/v2/app/setPreferences" \
                  --data "json={\"listen_port\": $mapped_port}"

                qbt_refresh_port
        else
            echo "Mapped port has not changed. Skipping qBittorrent port update."
        fi
    else
        echo "ERROR: Failed to extract Mapped public port from natpmpc output"
    fi

    sleep 45
done

instrs.txt

you need to change qbittorrent setting to bypass authentication on localhost 
- WebUI -> Authentication -> tick Bypass authentiction for clients on localhost

Works both docker and standalone as long as bittorrent is listening on localhost interface. when using docker i suggest changing the docker compose to either forward all ports or use **hosts** network mode

The autonat.service file goes inside the `/etc/systemd/system/` folder