added podman transparent setup (fix #448)

README.md

@@ -59,6 +59,7 @@ interfaces. The principle and basic setup is described
 [here](doc/simple_transparent_proxy.md), with further
 scenarios described [there](doc/scenarios-for-simple-transparent-proxy.md).
 
+There is also a guide to use [podman](doc/podman.md).
 
 Another method uses iptable packet marking features, and is
 highly dependent on your network environment and

doc/podman.md

@@ -0,0 +1,120 @@
+Here is an example of deployment of sslh in transparent mode
+using ansible and podman, [submitted by Github user
+olegstepura](https://github.com/yrutschle/sslh/issues/448)
+
+```yaml
+# 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
+```
+
+```ini
+# 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.
+