Seamless haproxy on marathon-lb w/ systemd

haproxy_cluster_vars.conf

# /etc/systemd/system/haproxy.service.d/haproxy_cluster_vars.conf
[Service]
Environment="PIDFILE=/run/haproxy.pid"
Environment="HAPROXY_SOCKET=/var/run/haproxy/socket"

# Get rid of the socket on start/stop
ExecStartPre=/bin/bash -c "rm -f $HAPROXY_SOCKET"
ExecStopPost=/bin/bash -c "rm -f $HAPROXY_SOCKET"

# XXX: Do seamless reloads
ExecReload=
ExecReload=/usr/sbin/haproxy -c -f ${CONFIG}
ExecReload=-/bin/bash -c 'echo > /var/state/haproxy/global && \
                          /usr/bin/socat /var/run/haproxy/socket - <<< "show servers state" > /var/state/haproxy/global'
ExecReload=/bin/kill -USR2 $MAINPID