systemd-socket-proxyd

systemd
systemd-socket-proxyd
8
systemd-socket-proxyd
Bidirectionally proxy local sockets to another (possibly remote) socket
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:
--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.
--proxy-protocol=
Uses the PROXY protocol to communicate with the server. This allows an appropriately configured server to know the real client IP address. Takes the version of the PROXY protocol used, and only supports 
v1 for now. Default is not to use a PROXY protocol.
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.
proxy-to-nginx.socket
[Socket]
ListenStream=80
[Install]
WantedBy=sockets.target
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
nginx.conf
[…]
server {
    listen       unix:/run/nginx/socket;
    […]
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.
proxy-to-nginx.socket
[Socket]
ListenStream=80
[Install]
WantedBy=sockets.target
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
nginx.conf
[…]
server {
    listen       8080;
    […]
Enabling the proxy
# systemctl enable --now proxy-to-nginx.socket
$ curl http://localhost:80/
PROXY protocol example with nginx
systemd-socket-proxyd and nginx using the PROXY protocol
proxy-to-nginx.socket
[Socket]
ListenStream=80
[Install]
WantedBy=sockets.target
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 --proxy-protocol=v1 /run/nginx/socket
PrivateTmp=yes
PrivateNetwork=yes
nginx.conf
[…]
server {
    listen         unix:/run/nginx/socket proxy_protocol;
    real_ip_header proxy_protocol;
    […]
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), PROXY protocol specification, nginx: Accepting the PROXY Protocol