SSLH transparent with podman pod

[Oleg Stepura]

This is rather a success report, not an issue. Please let me know if you would like me to submit a pull request to update docs.

In my case I made it work with podman utilizing pods
I'm using ansible to deploy containers, but syntax is pretty similar to docker compose.

# ansible podman task
- name: "Create sslh-co pod"
  containers.podman.podman_pod:
    name: sslh-co # read as "sslh and company"
    state: started
    ports:
      - "80:80"
      - "443:444"
      # ... (more ports if needed)
    network:
      - '{{ containers.config.network }}' # other services from this network can access containers in this network for example prometheus can read caddy metrics at sslh-co:2020, also caddy itself can connect to other services to act as a reverse proxy

- name: "Create the sslh container"
  containers.podman.podman_container:
    name: sslh
    image: "yrutschle/sslh:latest"
    pod: sslh-co
    capabilities:
      - NET_RAW
      - NET_BIND_SERVICE
      - NET_ADMIN
    sysctl:
      net.ipv4.conf.default.route_localnet: 1
      net.ipv4.conf.all.route_localnet: 1
    expose:
      - 444
    volume:
      # ... (make sure to mount config as you like)
    command: --transparent -F/etc/sslh/sslh.cfg # parameter --transparent here is needed to trigger configure_iptables in init script
   state: started

- name: "Create the caddy container"
  containers.podman.podman_container:
    name: caddy
    image: "lucaslorentz/caddy-docker-proxy:alpine" # regular caddy or nginx image will also work
    pod: sslh-co
    expose:
      - 80
      - 443
      - 2020 # metrics, since caddy-docker-proxy uses :2019 internally
    volume:
      # ... (mount your configs and other stuff here)
      - "/var/run/podman/podman.sock:/var/run/docker.sock"
    state: started
  notify: podman restart sslh

- name: "Create the SSH proxy to host container"
  containers.podman.podman_container:
    name: ssh-proxy
    image: "alpine/socat:latest"
    pod: sslh-co
    expose:
      - 222
    command: TCP-LISTEN:222,fork TCP:host.containers.internal:22
    state: started

# sslh config
foreground: true;
inetd: false;
numeric: true;
transparent: true;
timeout: 5;

listen:
(
    { host: "0.0.0.0"; port: "444"; keepalive: true; },
);

protocols:
(
  {
    name: "ssh";
    service: "ssh";
    host: "localhost";
    port: "222";
    fork: true;
  },
  {
    name: "http";
    host: "localhost";
    port: "80";
  },
  {
    name: "tls";
    host: "localhost";
    port: "443";
  },
);

I omitted caddy configs here as it's not important. Some unrelated container configs were also dropped.
In the example above sslh, caddy and ssh-proxy are 3 containers in the same pod, all listening on localhost. SSLH has to listen on 444 because caddy already listens on 443 and it's more complex to reconfigure caddy port because of let's encrypt (caddy itself "thinks" it is bound to your host interface).

Scheme of port mapping is (all containers share same localhost):

host 443 → pod 444 (sslh) → pod 443 (caddy)

• podman connects host 443 port to pod's 444 port
• sslh listens 444 on localhost, reroutes tls to caddy on localhost:443
• caddy listens 443 on localhost (reverse-proxies to other apps on private network)
  Reverse-proxied services get correct IP in X-Forwarded-For header.

Takeaways:

• net.ipv4.conf.default.route_localnet is setup only in container, not on host, which is nice.
• same with iptables and route rules applied by init script in sslh container
• sslh proxy to other services in the private network will not work (because transparent mode is enabled) even if that other service does not need real IP
  • with transparent mode all services that sslh will connect to should be attached to this pod making it listen on localhost of the pod
  • ports of containers should not clash
  • ports should be published on pod level, not on containers
  • containers should not be configured to connect to custom networks
• because of the above proxying ssh to host will also not work out of the box, sslh should connect to localhost and not to a random IP. While adding another proxy as a container to the same pod sounds like an overkill I don't see any other solution, so socat is used as an additional proxy.
• reverse_proxy by caddy to other containers in the same custom network (as pod is attached to) works (e.g. caddy can connect to other IPs from custom network). socat can also connect to host and/or other containers in custom network.

[Yves Rutschle]

yes, this would be perfect as a PR in a new doc/podman.md file. thanks in advance!