Selfhosted

I think you already have a kill-switch (of sorts) in place with the two Wireguard container setup, since your clients lose internet access (except to the local network, since there's a separate route for that on the Wireguard "server" container") if any of the following happens:

• "Client" container is spun down
• The Wireguard interface inside the "client" container is spun down (you can try this out by execing wg-quick down wg0 inside the container)
• or even if the interface is up but the VPN connection is down (try changing the endpoint IP to a random one instead of the correct one provided by your VPN service provider)

I can't be 100% sure, because I'm not a networking expert, but this seems like enough of a "kill-switch" to me. I'm not sure what you mean by leveraging the restart. One of the things that I found annoying about the Gluetun approach is that I would have to restart every container that depends on its network stack if Gluetun itself got restarted/updated.

But anyway, I went ahead and messed around on a VPS with the Wireguard+Gluetun approach and I got it working. I am using the latest versions of The Linuxserver.io Wireguard container and Gluetun at the time of writing. There are two things missing in the Gluetun firewall configuration you posted:

• A MASQUERADE rule on the tunnel, meaning the tun0 interface.
• Gluetun is configured to drop all FORWARD packets (filter table) by default. You'll have to change that chain rule to ACCEPT. Again, I'm not a networking expert, so I'm not sure whether or not this compromises the kill-switch in any way, at least in any way that's relevant to the desired setup/behavior. You could potentially set a more restrictive rule to only allow traffic coming in from <wireguard_container_IP>, but I'll leave that up to you. You'll also need to figure out the best way to persist the rules through container restarts.

First, here's the docker compose setup I used:

networks:
  wghomenet:
    name: wghomenet
    ipam:
      config:
        - subnet: 172.22.0.0/24
          gateway: 172.22.0.1

services:
  gluetun:
    image: qmcgaw/gluetun
    container_name: gluetun
    cap_add:
      - NET_ADMIN
    devices:
      - /dev/net/tun:/dev/net/tun
    ports:
      - 8888:8888/tcp # HTTP proxy
      - 8388:8388/tcp # Shadowsocks
      - 8388:8388/udp # Shadowsocks
    volumes:
      - ./config:/gluetun
    environment:
      - VPN_SERVICE_PROVIDER=<your stuff here>
      - VPN_TYPE=wireguard
      # - WIREGUARD_PRIVATE_KEY=<your stuff here>
      # - WIREGUARD_PRESHARED_KEY=<your stuff here>
      # - WIREGUARD_ADDRESSES=<your stuff here>
      # - SERVER_COUNTRIES=<your stuff here>
      # Timezone for accurate log times
      - TZ= <your stuff here>
      # Server list updater
      # See https://github.com/qdm12/gluetun-wiki/blob/main/setup/servers.md#update-the-vpn-servers-list
      - UPDATER_PERIOD=24h
    sysctls:
      - net.ipv4.conf.all.src_valid_mark=1
    networks:
      wghomenet:
        ipv4_address: 172.22.0.101

  wireguard-server:
    image: lscr.io/linuxserver/wireguard
    container_name: wireguard-server
    cap_add:
      - NET_ADMIN
    environment:
      - PUID=1000
      - PGID=1001
      - TZ=<your stuff here>
      - INTERNAL_SUBNET=10.13.13.0
      - PEERS=chromebook
    volumes:
      - ./config/wg-server:/config
      - /lib/modules:/lib/modules #optional
    restart: always
    ports:
      - 51820:51820/udp
    networks:
      wghomenet:
        ipv4_address: 172.22.0.5
    sysctls:
      - net.ipv4.conf.all.src_valid_mark=1

You already have your "server" container properly configured. Now for Gluetun: I exec into the container docker exec -it gluetun sh. Then I set the MASQUERADE rule on the tunnel: iptables -t nat -A POSTROUTING -o tun+ -j MASQUERADE. And finally, I change the FORWARD chain policy in the filter table to ACCEPT iptables -t filter -P FORWARD ACCEPT.

Note on the last command: In my case I did iptables-legacy because all the rules were defined there already (iptables gives you a warning if that's the case), but your container's version may vary. I saw different behavior on the testing container I spun up on the VPS compared to the one I have running on my homelab.

Good luck, and let me know if you run into any issues!

EDIT: The rules look like this afterwards:

Output of iptables-legacy -vL -t filter:

Chain INPUT (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
10710  788K ACCEPT     all  --  lo     any     anywhere             anywhere
16698   14M ACCEPT     all  --  any    any     anywhere             anywhere             ctstate RELATED,ESTABLISHED
    1    40 ACCEPT     all  --  eth0   any     anywhere             172.22.0.0/24

# note the ACCEPT policy here
Chain FORWARD (policy ACCEPT 3593 packets, 1681K bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain OUTPUT (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
10710  788K ACCEPT     all  --  any    lo      anywhere             anywhere
13394 1518K ACCEPT     all  --  any    any     anywhere             anywhere             ctstate RELATED,ESTABLISHED
    0     0 ACCEPT     all  --  any    eth0    dac4b9c06987         172.22.0.0/24
    1   176 ACCEPT     udp  --  any    eth0    anywhere             connected-by.global-layer.com  udp dpt:1637
  916 55072 ACCEPT     all  --  any    tun0    anywhere             anywhere

And the output of iptables -vL -t nat:

Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 DOCKER_OUTPUT  all  --  any    any     anywhere             127.0.0.11

# note the MASQUERADE rule here
Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 DOCKER_POSTROUTING  all  --  any    any     anywhere             127.0.0.11
  312 18936 MASQUERADE  all  --  any    tun+    anywhere             anywhere

Chain DOCKER_OUTPUT (1 references)
 pkts bytes target     prot opt in     out     source               destination
    0     0 DNAT       tcp  --  any    any     anywhere             127.0.0.11           tcp dpt:domain to:127.0.0.11:39905
    0     0 DNAT       udp  --  any    any     anywhere             127.0.0.11           udp dpt:domain to:127.0.0.11:56734

Chain DOCKER_POSTROUTING (1 references)
 pkts bytes target     prot opt in     out     source               destination
    0     0 SNAT       tcp  --  any    any     127.0.0.11           anywhere             tcp spt:39905 to::53
    0     0 SNAT       udp  --  any    any     127.0.0.11           anywhere             udp spt:56734 to::53