SYSTEMD-SOCKET-PROXYD(8)

NAME
systemd-socket-proxyd - Bidirectionally proxy local sockets to another (possibly remote) socket

SYNOPSIS

systemd-socket-proxyd [OPTIONS...] HOST:PORT

systemd-socket-proxyd [OPTIONS...] UNIX-DOMAIN-SOCKET-PATH

DESCRIPTION

systemd-socket-proxyd is a generic socket-activated network socket forwarder proxy daemon for IPv4, IPv6 and UNIX stream sockets. It may be used to bi-directionally forward traffic from a local listening socket to a local or remote destination socket.

One use of this tool is to provide socket activation support for services that do not natively support socket activation. On behalf of the service to activate, the proxy inherits the socket from systemd, accepts each client connection, opens a connection to a configured server for each client, and then bidirectionally forwards data between the two.

This utility's behavior is similar to socat(1). The main differences for systemd-socket-proxyd are support for socket activation with "Accept=no" and an event-driven design that scales better with the number of connections.

Note that systemd-socket-proxyd will not forward socket side channel information, i.e. will not forward SCM_RIGHTS, SCM_CREDENTIALS, SCM_SECURITY, SO_PEERCRED, SO_PEERPIDFD, SO_PEERSEC, SO_PEERGROUPS and similar.

OPTIONS

The following options are understood:

-h, --help
    Print a short help text and exit.

--version
    Print a short version string and exit.

--connections-max=, -c
    Sets the maximum number of simultaneous connections, defaults to 256. If the limit of concurrent connections is reached further connections will be refused.

--exit-idle-time=
    Sets the time before exiting when there are no connections, defaults to infinity. Takes a unit-less value in seconds, or a time span value such as "5min 20s".

EXIT STATUS

On success, 0 is returned, a non-zero failure code otherwise.

EXAMPLES

  Simple Example

Use two services with a dependency and no namespace isolation.

Example 1. proxy-to-nginx.socket

    [Socket]
    ListenStream=80

    [Install]
    WantedBy=sockets.target

Example 2. proxy-to-nginx.service

    [Unit]
    Requires=nginx.service
    After=nginx.service
    Requires=proxy-to-nginx.socket
    After=proxy-to-nginx.socket

    [Service]
    ExecStart=/lib/systemd/systemd-socket-proxyd /run/nginx/socket
    PrivateTmp=yes
    PrivateNetwork=yes

Example 3. nginx.conf

    [...]
    server {
        listen       unix:/run/nginx/socket;
        [...]

Example 4. Enabling the proxy

    # systemctl enable --now proxy-to-nginx.socket
    $ curl http://localhost:80/

If nginx.service has StopWhenUnneeded= set, then passing --exit-idle-time= to systemd-socket-proxyd allows both services to stop during idle periods.

  Namespace Example

Similar as above, but runs the socket proxy and the main service in the same private namespace, assuming that nginx.service has PrivateTmp= and PrivateNetwork= set, too.

Example 5. proxy-to-nginx.socket

    [Socket]
    ListenStream=80

    [Install]
    WantedBy=sockets.target

Example 6. proxy-to-nginx.service

    [Unit]
    Requires=nginx.service
    After=nginx.service
    Requires=proxy-to-nginx.socket
    After=proxy-to-nginx.socket
    JoinsNamespaceOf=nginx.service

    [Service]
    ExecStart=/lib/systemd/systemd-socket-proxyd 127.0.0.1:8080
    PrivateTmp=yes
    PrivateNetwork=yes

Example 7. nginx.conf

    [...]
    server {
        listen       8080;
        [...]

Example 8. Enabling the proxy

    # systemctl enable --now proxy-to-nginx.socket
    $ curl http://localhost:80/

SEE ALSO

systemd(1), systemd.socket(5), systemd.service(5), systemctl(1), socat(1), nginx(1), curl(1)