Systemd integration

A Pingora server doesn't depend on systemd but it can easily be made into a systemd service.

[Service]
Type=forking
PIDFile=/run/pingora.pid
ExecStart=/bin/pingora -d -c /etc/pingora.conf
ExecReload=kill -QUIT $MAINPID
ExecReload=/bin/pingora -u -d -c /etc/pingora.conf

The example systemd setup integrates Pingora's graceful upgrade into systemd. To upgrade the pingora service, simply install a version of the binary and then call systemctl reload pingora.service.