haproxy.conf.erb stats directive makes haproxy service unavailable (service down)

[NVitanovic]

When service is started/restarted this message appears on status.

root@lb1:~# service haproxy status
● haproxy.service - HAProxy Load Balancer
   Loaded: loaded (/lib/systemd/system/haproxy.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Tue 2017-12-26 06:24:08 EST; 16s ago
     Docs: man:haproxy(1)
           file:/usr/share/doc/haproxy/configuration.txt.gz
  Process: 6055 ExecStart=/usr/sbin/haproxy-systemd-wrapper -f ${CONFIG} -p /run/haproxy.pid $EXTRAOPTS (code=exited, status=0/SUCCESS)
  Process: 6051 ExecStartPre=/usr/sbin/haproxy -f ${CONFIG} -c -q (code=exited, status=0/SUCCESS)
 Main PID: 6055 (code=exited, status=0/SUCCESS)

Dec 26 06:24:08 lb1 systemd[1]: haproxy.service: Service hold-off time over, scheduling restart.
Dec 26 06:24:08 lb1 systemd[1]: Stopped HAProxy Load Balancer.
Dec 26 06:24:08 lb1 systemd[1]: haproxy.service: Start request repeated too quickly.
Dec 26 06:24:08 lb1 systemd[1]: Failed to start HAProxy Load Balancer.

More detailed error when haproxy is run in debug mode:

root@lb1:~# haproxy -f /etc/haproxy/haproxy.cfg -d
[WARNING] 359/063924 (6754) : parsing [/etc/haproxy/haproxy.cfg:91] : 'balance' ignored because frontend 'ftpcluster' has no backend capability.
[WARNING] 359/063924 (6754) : parsing [/etc/haproxy/haproxy.cfg:93] : 'stick' ignored because frontend 'ftpcluster' has no backend capability.
Available polling systems :
      epoll : pref=300,  test result OK
       poll : pref=200,  test result OK
     select : pref=150,  test result FAILED
Total: 3 (2 usable), will use epoll.
Using epoll() as the polling mechanism.
[ALERT] 359/063924 (6754) : Starting frontend GLOBAL: error when trying to preserve previous UNIX socket [/var/run/haproxy]

Solution is to remove/comment the following lines in haproxy.conf.erb:

stats socket /run/haproxy/admin.sock mode 660 level admin
stats timeout 30s
stats socket /var/run/haproxy

After that service starts without problems.