TBH I haven’t played with passing caddy’s podman network to other containers, mine is a simple reverse proxy to other standalone containers but not directly connected via podman run --network (or quadlet network). In my scenario I can at least confirm that net.ipv4.ip_unprivileged_port_start doesn’t need to be modified, the only annoyance is that I cannot use a systemd user service, even though the end process doesn’t run as root.

EDIT: Actually looking at the examples a bit more closely I think the primary difference with my setup is that the systemd socket is started with systemd --user which thus requires the sysctl change, whereas I’m not using a systemd user service, relying instead on User=some-non-root-user to use rootless podman, but requiring root privileges to manage the systemd service.

You can use rootless caddy via systemd socket activation, here’s a basic setup:

1. rootless-caddy.service

[Unit]
Description=rootless-caddy

Requires=rootless-caddy.socket
After=rootless-caddy.socket

[Service]
# a non root user here
User=El_Quentinator
ExecStart=podman run --name caddy --rm -v [...] docker.io/caddy:alpine

[Install]
WantedBy=default.target

2. rootless-caddy.socket

[Socket]
BindIPv6Only=both

### sockets for the HTTP reverse proxy
# fd/3
ListenStream=[::]:443

# fdgram/4
ListenDatagram=[::]:443

[Install]
WantedBy=sockets.target

3. Caddyfile

{$SITE_ADDRESS} {
        # tcp/443
        bind fd/3 {
                protocols h1 h2
        }
        # udp/443
        bind fdgram/4 {
                protocols h3
        }
        [...]
}

And that’s it really.

You can find a few more examples over here: https://github.com/eriksjolund/podman-caddy-socket-activation

Systemd socket activation has a few more interesting advantages on top of unlocking binding priviliged ports:

• allowing to not bind any port on the container, which itself allows to use --network none while still being able to connect to it via systemd socket, pretty neat to expose some web app while completely cutting its own external access.
• getting rootful networking performance
• starting up your service only when connecting to it (and potentially shutting it back down after some time)

Drawbacks is that the file descriptor binding is a bit awkward and not always supported (caddy/nginx/haproxy do support it though). And that podman pods / kube do not support it (or at least not yet).