I looked at this page and wonder how this is suppose to work:
# Control the maintenance page during runtime using the stats socket:
#
# To put the whole site in maintenance mode (for all IPs):
# > add acl #0 0.0.0.0/0
#
# To exclude your own ip, so you are able to test things out:
# > add acl #1 8.8.8.8
#
# To exit maintenance mode again simply remove the mask from #0 again:
# > del acl #0 0.0.0.0/0
Where and when should I use this commands? For me it looks like it shall be entered from the shell or should I uncomment the lines an restart haproxy?
First sentence: Control the maintenance page during runtime using the stats socket
Which mean???
(I’m a complete novice with haproxy)
You can configure a socket on the machine hosting HAPROXY to send commands via the CML to haproxy.
Similar to the /stats page.
you can check the install documentation to tell you how to make the socket.
Thanks a lot. I’ll check this. 
The only problem now is that the way of doing this (as described in the document in the link) does not work. I get a failure when restarting haproxy. I’m currently not able to find out why.
BTW, I have version 1.5.8