gluetun:
    image: qmcgaw/gluetun
    container_name: gluetun-wireguard
    restart: unless-stopped
    cap_add:
      - NET_ADMIN
    devices:
      - /dev/net/tun:/dev/net/tun
    volumes:
      - ./gluetun:/gluetun
    environment:
      - VPN_SERVICE_PROVIDER=#
      - VPN_TYPE=wireguard
      - WIREGUARD_PRIVATE_KEY=#
      - WIREGUARD_ADDRESSES=#
      - SERVER_CITIES=#setup#setup
      # Timezone for accurate log times
      - TZ=#
      # Server list updater
      # See https://github.com/qdm12/gluetun-wiki/blob/main/setup/servers.md#update-the-vpn-servers-list
      - UPDATER_PERIOD=24h
    ports:
      - 51820:51820/udp
  wireguard-server:
    image: linuxserver/wireguard
    containe

Hello there,

Just want to preface that this is for selfhosted purposes, I may be routing my network in other way later.

I wanted to be able to setup a wireguard docker container with gluetun such that I can connect multiple devices to it at home, in order to minimize my "five device limit" with mullvad. I have the following docker compose:

  gluetun:
    image: qmcgaw/gluetun
    container_name: gluetun-wireguard
    restart: unless-stopped
    cap_add:
      - NET_ADMIN
    devices:
      - /dev/net/tun:/dev/net/tun
    volumes:
      - ./gluetun:/gluetun
    environment:
      - VPN_SERVICE_PROVIDER=#
      - VPN_TYPE=wireguard
      - WIREGUARD_PRIVATE_KEY=#
      - WIREGUARD_ADDRESSES=#
      - SERVER_CITIES=#setup#setup
      # Timezone for accurate log times
      - TZ=#
      # Server list updater
      # See https://github.com/qdm12/gluetun-wiki/blob/main/setup/servers.md#update-the-vpn-servers-list
      - UPDATER_PERIOD=24h
    ports:
      - 51820:51820/udp
  wireguard-server:
    image: linuxserver/wireguard
    container_name: wireguard-server
    network_mode: service:gluetun # << important
    cap_add:
      - NET_ADMIN
      - SYS_MODULE
    environment:
      - PUID=1000
      - PGID=1000
      - SERVERPORT=51820
      - PEERS=iphone
      - PEERDNS=auto
    volumes:
      - ./config:/config
      - /lib/modules:/lib/modules
    restart: unless-stopped

Whenever I try connecting to it by iphone, which is my first attempt for the peer, it doesn't quite work out.
The packets are received by the container, and querying cloudflare as such works:

$ sudo docker exec -it wireguard-server ping -c 3 1.1.1.1

Is there any obvious error I've made?

If I'm making the XY Problem, please let me know. If there is a more apt community, please let me know.