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.

           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.

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]
           Type=notify
           ExecStart=/usr/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]
           Type=notify
           ExecStart=/usr/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)