cat /etc/init/persistent-mysql-tunnel.conf

persistent-mysql-tunnel.conf

# persistent-mysql-tunnel

description "Set up a persistent mysql tunnel (using autossh)"
author      "Mischa ter Smitten"

start on net-device-up IFACE=eth0
stop on runlevel [01S6]

respawn
respawn limit 5 60 # Respawn max 5 times in 60 seconds
umask 022

pre-start script
  test -x /usr/bin/autossh || { stop; exit 0; }

  mkdir -p -m0755 /var/run/autossh
end script

script
  export AUTOSSH_PIDFILE=/var/run/autossh/persistent-mysql-tunnel.pid
  export AUTOSSH_POLL=60
  export AUTOSSH_FIRST_POLL=30
  export AUTOSSH_GATETIME=0
  export AUTOSSH_DEBUG=1

  autossh -M 0 -4 -N -L 3307:127.0.0.1:3306 autossh@example.com -p 22 -i /etc/autossh/id_rsa -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -o "BatchMode=yes" -o "StrictHostKeyChecking=no"
end script

Restart the tunnel like this:

restart persistent-mysql-tunnel;

Put this file in /etc/init/