Routing wg-easy container traffic through Gluetun container

docker-compose.yml

# https://gist.github.com/skylerwlewis/f009741cd20d8ab86ce65d67accccc3f
#
# This is a Gluetun + wg-easy docker compose setup based on instructions I found here:
# https://lemmy.max-p.me/post/midwest.social/14630711
#
# In addition to the logic in the link above, I added:
#   - wg-easy to simplify client setup and PostUp & PostDown modifications
#   - Auto-restart capability for wg-easy container if Gluetun goes down
#
# If you are using 172.22.0.0/24 already, simply change "172.22" to a different subnet.
#
# If you use a different local network (other than 192.168.1.0/24),
# replace "192.168.1.0/24" in the config below with your local network
#
# If you need to run on different ports, or want to run multiple copies of the setup below:
#   Use a different gluetun healthcheck port (default 9999):
#     - Under gluetun's ports, change "9999:9999/tcp" to "<updated port>:9999/tcp"
#     - Replace all other instances of 9999 in this file with the updated port
#   Use a different wireguard port (default 51820):
#     - Replace all instances of 51820 in this file with the updated port
#   Use a different wg-easy UI port (default 51821):
#     - Replace all instances of 51821 in this file with the updated port
#
# A version of this setup using Wireguard-UI can be found here:
#   https://gist.github.com/skylerwlewis/50dd3dd628a5198ea29cfbcbf21783ac

networks:
  default:
    ipam:
      config:
        - subnet: 172.22.0.0/24

services:
  gluetun:
    image: qmcgaw/gluetun
    cap_add:
      - NET_ADMIN
    devices:
      - /dev/net/tun:/dev/net/tun
    environment:
      PUID: 1000
      PGID: 1000
      TZ: "America/Chicago"
      # See https://github.com/qdm12/gluetun-wiki/tree/main/setup/providers
      # for information on how to setup gluetun for different VPN providers.
      # An example of a Mullvad Wireguard setup is below
      VPN_SERVICE_PROVIDER: mullvad
      VPN_TYPE: wireguard
      WIREGUARD_PRIVATE_KEY: <PrivateKey_value_from_cilent_.conf_file>
      OWNED_ONLY: yes  # if uncommented, gluetun will use only Mullvad-owned servers
      WIREGUARD_ADDRESSES: <Addresses_value_from_cilent_.conf_file>
      SERVER_CITIES: "Amsterdam"
      UPDATER_PERIOD: 24h
    volumes:
      - ./data/gluetun/conf:/gluetun
    sysctls:
      # Disables ipv6
      - net.ipv6.conf.all.disable_ipv6=1
    restart: unless-stopped
    networks:
      default:
        ipv4_address: 172.22.0.100
    ports:
      # port of the gluetun healthcheck server
      - 9999:9999/tcp
    configs:
      # allows wireguard to send traffic through gluetun
      # https://github.com/qdm12/gluetun-wiki/blob/main/setup/options/firewall.md#custom-iptables-rules
      - source: post-rules.txt
        target: /iptables/post-rules.txt

  wg-easy:
    environment:
      # Change Language:
      # (Supports: en, ua, ru, tr, no, pl, fr, de, ca, es, ko, vi, nl, is, pt, chs, cht, it, th, hi, ja, si)
      - LANG=en
      # ⚠️ Required:
      # Change this to your host's public address
      - WG_HOST=wireguard.example.com
      # Optional:
      # - PASSWORD_HASH=$$2y$$10$$hBCoykrB95WSzuV4fafBzOHWKu9sbyVa34GJr8VV5R/pIelfEMYyG # (needs double $$, hash of 'foobar123'; see "How_to_generate_an_bcrypt_hash.md" for generate the hash)
      - PORT=51821
      - WG_PORT=51820
      # - WG_CONFIG_PORT=92820
      # - WG_DEFAULT_ADDRESS=10.8.0.x
      - WG_DEFAULT_DNS=172.22.0.100
      # - WG_MTU=1420
      # - WG_ALLOWED_IPS=192.168.15.0/24, 10.0.1.0/24
      # - WG_PERSISTENT_KEEPALIVE=25
      # - WG_PRE_UP=echo "Pre Up" > /etc/wireguard/pre-up.txt
      - WG_POST_UP=iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o eth+ -j MASQUERADE; wg set wg0 fwmark 51820; ip -4 rule add not fwmark 51820 table 51820; ip -4 rule add table main suppress_prefixlength 0; ip -4 route add 0.0.0.0/0 via 172.22.0.100 table 51820; ip -4 route add 192.168.1.0/24 via 172.22.0.1
      # - WG_PRE_DOWN=echo "Pre Down" > /etc/wireguard/pre-down.txt
      - WG_POST_DOWN=iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o eth+ -j MASQUERADE
      # - UI_TRAFFIC_STATS=true
      # - UI_CHART_TYPE=0 # (0 Charts disabled, 1 # Line chart, 2 # Area chart, 3 # Bar chart)
      # - WG_ENABLE_ONE_TIME_LINKS=true
      # - UI_ENABLE_SORT_CLIENTS=true
      # - WG_ENABLE_EXPIRES_TIME=true
      # - ENABLE_PROMETHEUS_METRICS=false
      # - PROMETHEUS_METRICS_PASSWORD=$$2a$$12$$vkvKpeEAHD78gasyawIod.1leBMKg8sBwKW.pQyNsq78bXV3INf2G # (needs double $$, hash of 'prometheus_password'; see "How_to_generate_an_bcrypt_hash.md" for generate the hash)
    image: ghcr.io/wg-easy/wg-easy
    container_name: wg-easy
    volumes:
      - ./data/wireguard:/etc/wireguard
    ports:
      - "51820:51820/udp"
      - "51821:51821/tcp"
    healthcheck:
      # check health of gluetun container, and auto-restart if gluetun is unhealthy
      test: "nc -z 172.22.0.1 9999 || kill 1"
      interval: 1m
      timeout: 1m
    restart: unless-stopped
    networks:
      default:
        ipv4_address: 172.22.0.2
    cap_add:
      - NET_ADMIN
      - SYS_MODULE
      # - NET_RAW # ⚠️ Uncomment if using Podman
    sysctls:
      - net.ipv4.ip_forward=1
      - net.ipv4.conf.all.src_valid_mark=1

configs:
  post-rules.txt:
    content: |
      iptables -t nat -A POSTROUTING -o tun+ -j MASQUERADE
      iptables -t filter -A FORWARD -d 172.22.0.2 -j ACCEPT
      iptables -t filter -A FORWARD -s 172.22.0.2 -j ACCEPT

Going to share this here too. I've been trying to do use WG and Gluetun to make a single wireguard connection that'll route outgoing traffic through Mullvad, while also allowing me to access my LAN. This compose was working for the former, but not the latter. I found someone else's example which gave me the same results.

After bashing my head against the wall for a bit and learning more than I expected to about iptables, I have a version that does exactly what I want:

qdm12/gluetun#1192 (reply in thread)