Hmmm

https://www.samandfuzzy.com

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

Gluetun likely doesn’t have the proper firewall rules in place to enable this sort of traffic routing, simply because it’s made for another use case (using the container’s network stack directly with network_mode: "service:gluetun").

Try to first get this setup working with two vanilla Wireguard containers (instead of Wireguard + gluetun). If it does, you’ll know that your Wireguard “server” container is properly set up. Then replace the second container that’s acting as a VPN client with gluetun and run tcpdump again. You likely need to add a postrouting masquerade rule on the NAT table.

Here’s my own working setup for reference.

Wireguard “server” container:

[Interface]
Address = <address>
ListenPort = 51820
PrivateKey = <privateKey>
PostUp = iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
PostUp = wg set wg0 fwmark 51820
PostUp = ip -4 route add 0.0.0.0/0 via 172.22.0.101 table 51820
PostUp = ip -4 rule add not fwmark 51820 table 51820
PostUp = ip -4 rule add table main suppress_prefixlength 0
PostUp = ip route add 192.168.16.0/24 via 172.22.0.1
PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE; ip route del 192.168.16.0/24 via 172.22.0.1

#peer configurations (clients) go here

and the Wireguard VPN client that I route traffic through:

# Based on my VPN provider's configuration + additional firewall rules to route traffic correctly
[Interface]
PrivateKey = <key>
Address = <address>
DNS = 192.168.16.81 # local Adguard
PostUp = iptables -t nat -A POSTROUTING -o wg+ -j MASQUERADE #Route traffic coming in from outside the container (host/other container)
PreDown = iptables -t nat -D POSTROUTING -o wg+ -j MASQUERADE

[Peer]
PublicKey = <key>
AllowedIPs = 0.0.0.0/0
Endpoint = <endpoint_IP>:51820

Note the NAT MASQUERADE rule.