Helper container to pass forwarded port to Deluge

Dockerfile

FROM alpine:latest
RUN echo "http://dl-cdn.alpinelinux.org/alpine/edge/testing/" >> /etc/apk/repositories && \
    echo "http://dl-cdn.alpinelinux.org/alpine/edge/community/" >> /etc/apk/repositories && \
    echo "http://dl-cdn.alpinelinux.org/alpine/edge/main/" >> /etc/apk/repositories && \
    apk add --no-cache bash deluge
ADD pia-port.sh /scripts/pia-port.sh
RUN chmod +x /scripts/*.sh
CMD ["/scripts/pia-port.sh"]

pia-port.sh

#!/bin/bash

trap 'exit 0' SIGTERM

OLDPORT=0
PORT=0

while true
do
  [ -r "/pia-shared/port.dat" ] && PORT=$(cat /pia-shared/port.dat)

  if [ $OLDPORT -ne $PORT ]; then
    echo "Setting Deluge port settings ($PORT)..."
    deluge-console --config=/deluge/conf "config --set listen_ports ($PORT,$PORT)"
    OLDPORT=$PORT
  fi
  sleep 30 &
  wait $!
done

I wrote a post-up.sh script which saves the wg0 interface's IP address to /pia-shared/ip.dat and modified this script to update deluge automatically when it changes after a restart.
post-up.sh

#!/usr/bin/env bash

ifconfig wg0 | grep 'inet addr:' | cut -d: -f2| cut -d' ' -f1 > /pia-shared/ip.dat

pia-port.sh

#!/bin/bash

trap 'exit 0' SIGTERM

OLDPORT=0
PORT=0
OLD_IP=""
IP=""

while true
do
  [ -r "/pia-shared/port.dat" ] && PORT=$(cat /pia-shared/port.dat)
  [ -r "/pia-shared/ip.dat" ] && IP=$(cat /pia-shared/ip.dat)

  if [ $OLDPORT -ne $PORT ]; then
    echo "Setting Deluge port settings ($PORT)..."
    deluge-console --config=/deluge/conf "config --set listen_ports ($PORT,$PORT)"
    OLDPORT=$PORT
  fi

  if [[ $OLD_IP != $IP ]]; then
    echo "Setting Deluge listen interface setting ($IP)..."
    deluge-console --config=/deluge/conf "config --set listen_interface $IP"
    OLD_IP=$IP
  fi
  sleep 30 &
  wait $!
done

Here's a version that works with an external Deluge instance and authenticates with a username and password.

In your docker-compose.yml

deluge-port-helper:
    restart: unless-stopped
    build: /path/to/deluge-port-helper
    volumes:
        - pia-shared:/pia-shared:ro
    network_mode: "service:vpn"
    depends_on:
        - vpn
    environment:
        - DELUGE_HOST=10.0.0.5
        - DELUGE_PORT=58846
        - DELUGE_USER=delugeuser
        - DELUGE_PASS=delugepass

pia-port.sh

#!/bin/bash

trap 'exit 0' SIGTERM

OLDPORT=0
PORT=0

while true
do
  [ -r "/pia-shared/port.dat" ] && PORT=$(cat /pia-shared/port.dat)

  if [ $OLDPORT -ne $PORT ]; then
    echo "Setting Deluge port settings ($PORT) on $DELUGE_HOST:$DELUGE_PORT"
    deluge-console "connect $DELUGE_HOST:$DELUGE_PORT $DELUGE_USER $DELUGE_PASS ; config --set listen_ports ($PORT,$PORT)"
    OLDPORT=$PORT
  fi
  sleep 30 &
  wait $!
done

If you need to add a user to deluge, add to ~/.config/deluge/auth and restart deluged
user:pass:10

Some recent change in Alpine started causing these errors coming from the deluge binary:

Error relocating /usr/lib/libpython3.12.so.1.0: pwritev2: symbol not found
Error relocating /usr/lib/libpython3.12.so.1.0: preadv2: symbol not found

The solution is to upgrade the musl package when building the container, so your Dockerfile would then look like:

FROM alpine:latest
RUN echo "http://dl-cdn.alpinelinux.org/alpine/edge/testing/" >> /etc/apk/repositories && \
    echo "http://dl-cdn.alpinelinux.org/alpine/edge/community/" >> /etc/apk/repositories && \
    echo "http://dl-cdn.alpinelinux.org/alpine/edge/main/" >> /etc/apk/repositories && \
    apk add --no-cache bash deluge && \
    apk upgrade musl
ADD pia-port.sh /scripts/pia-port.sh
RUN chmod +x /scripts/*.sh
CMD ["/scripts/pia-port.sh"]