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

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.

SimpleExample
       Use two services with a dependency and no namespace isolation.

       Example1.proxy-to-nginx.socket

           [Socket]
           ListenStream=80

           [Install]
           WantedBy=sockets.target

       Example2.proxy-to-nginx.service

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

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

       Example3.nginx.conf

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

       Example4.Enablingtheproxy

           # 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.

   NamespaceExample
       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.

       Example5.proxy-to-nginx.socket

           [Socket]
           ListenStream=80

           [Install]
           WantedBy=sockets.target

       Example6.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]
           Type=notify
           ExecStart=/usr/lib/systemd/systemd-socket-proxyd 127.0.0.1:8080
           PrivateTmp=yes
           PrivateNetwork=yes

       Example7.nginx.conf

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

       Example8.Enablingtheproxy

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

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

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

       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.

           Added in version 233.

       --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".

           Added in version 246.

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

systemd 257.7                                                                           SYSTEMD-SOCKET-PROXYD(8)

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