An autossh tunnel service

autossh.service

[Unit]
Description=An autossh tunnel service
After=network-online.target

[Service]
# -M 0 -> no monitoring
# -N -> Just open the connection and do nothing (not interactive)
# ServerAliveInterval, ServerAliveCountMax -> check per interval, reconnect if (fail > Max)
# ExitOnForwardFailure -> make sure forwardings have succeeded

# -L
# Forward Local
# localhost : 1111 : 140.116.x.x : 2222
# Connect to local’s port 1111 will forward to remote’s port 2222

# -R
# Forward remote
# localhost : 1111 : localhost : 2222
# Remote connect to its localhost’s port 1111 will forward to local’s 2222

# -i [ssh key]
# -p [PORT] [USER]@[HOST]

User=tunnel

Environment="AUTOSSH_GATETIME=0"

ExecStart=/usr/bin/autossh -M 0 -N \
-o "ServerAliveInterval 60" \
-o "ServerAliveCountMax 3" \
-o "ExitOnForwardFailure=yes" \
-L localhost:[PORT]:localhost:[PORT] \
-i /home/tunnel/.ssh/id_rsa \
-p [PORT] [USER]@[HOST]

ExecStop=/usr/bin/killall autossh

Restart=always
RestartSec=30

[Install]
WantedBy=multi-user.target