reaction/config/reaction.service

# vim: ft=systemd
[Unit]
WantedBy=multi-user.target

# See `man systemd.exec` and `man systemd.service` for most options below
[Service]
ExecStart=/path/to/reaction -c /etc/reaction.yml

# Create an iptables chain for reaction
ExecStartPre=/path/to/iptables -w -N reaction
# Set its default to ACCEPT
ExecStartPre=/path/to/iptables -w -A reaction -j ACCEPT
# Always accept 127.0.0.1
ExecStartPre=/path/to/iptables -w -I reaction 1 -s 127.0.0.1 -j ACCEPT
# Insert this chain as the first item of the INPUT chain (for incoming connections)
ExecStartPre=/path/to/iptables -w -I INPUT -p all -j reaction

# Remove the chain from the INPUT chain
ExecStopPost=/path/to/iptables -w -D INPUT -p all -j reaction
# Empty the chain
ExecStopPost=/path/to/iptables -w -F reaction
# Delete the chain
ExecStopPost=/path/to/iptables -w -X reaction

# Ask systemd to create /var/lib/reaction (/var/lib/ is implicit)
StateDirectory=reaction
# Ask systemd to create /run/reaction at runtime (/run/ is implicit)
RuntimeDirectory=reaction
# Start reaction in its state directory
WorkingDirectory=/var/lib/reaction