=head1 NAME

smokeping_master_slave - How run multiple districuted instances of SmokePing

=head1 OVERVIEW

Normally smokeping probes run their tests from the host where smokeping runs
to some target host and monitor the latency of the connection between the
two. 

The Master/Slave concept enables all smokeping probes to run remotely. The
use case for this is, that you use somokeping to measure the overall
connectivity of your network. If you are interested in seeing if you central
DNS server or your file server works for everyone, you could setup several
smokeping instances checking up on on the two servers from multiple
locations within your network. With the Master/Slave smokeping configuration
this process becomes much simpler, as one smokeping master server can
control multiple slaves.

All monitoring data is stored and presented on the server, but colleted by
the slaves. The slaves will also get their configuration information from
the master, so that you just have to maintain the master server
configuration file and the rest is taken care of automatically.

=head1 DESCRIPTION

=head2 Architecture

The master smokeping server communicates with it's slave servers through a
polling protocol. Whenever it assumes the slave should have new data ready
it will poll the slave. If the slave or the network is down, it will skip
the particular slave and move on to the next one.

When it polls a slave it will also tell the slave about any pending configuration
changes.

The communication between master and slave is digest authenticated. And
optionally runns over https.

              +---------------+
              |    master     |
              +---------------+
                |     |     |
        +-------+     |     +--------+
        v             v              v
    [slave 1]     [slave 2]      [slave 3]

The slave is a normal smokeping setup where the configuration comes from the
master instead of a local configuration file. The slave can run in two
modes. In standalone mode it will fork off a service process that listens
for incoming connections from the master. In cgi-mode the master connections
will be served by a cgi script. The connection part will communicate with
the local smokeping demon through a a perl storable file. The reason for
using a storable is that it will survive smokeping restartes and even
reboots if it is located on non-volatile storage.

=head2 Master Configuration

To configure a master/slave setup, add a slaves section to your smokeping
configuration file. The secret and timeout parameters will be inherited
by the slave config sections and can be overwritten if required.

 *** slaves ****
 secrets=/etc/smokeping/slavesecrets.conf 
 timeout=30
 +slave1
 url=http://....
 timeout=60
 ...

Then in the targets section you can define slaves at every lvel. Again the
settings get inherited by lower order targets and can be overwritten
anywhere in the tree.

A slave will then get the appropriate configuration assigned by the server.
 
 *** targets ***
 slaves = slave1 slave2
 ...
 +dest1
 slaves =
 ...
 +dest2
 slaves = slave1
 ...
 +dest3
 ... 

=head2 Slave Configuration

A smokeping slave setup has no configuration file. It just needs to know
that it runs in slave-mode. And a few configuration parameters depending on
your setup.

When running in B<cgi-mode>, the only configuration option is to specify the
location of communication cache file. By default this will be located in
F</tmp/smokeping.$USER.cache>. Authentication and access restrictions can be
configured using your webservers facilities.

 ./smokeping --slavemode=cgi --cache=/var/smokeping/cache.file

When running in standalone mode, the authentication parameters must be
configured in the smokeping daemon.

 ./smokeping --slavemode=standalone  --cache=/var/smokeping/cache.file \
             --auth-file=/etc/smokeping/digest.conf \
             --listen=ip:port \
             --ssl_listen=ip:port \
             --master-allow=128.223.22.2

=head1 COPYRIGHT

Copyright (c) 2007 by Tobias Oetiker, OETIKER+PARTNER AG. All right reserved.

=head1 LICENSE

This program is free software; you can redistribute it
and/or modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later
version.

This program is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.  See the GNU General Public License for more
details.

You should have received a copy of the GNU General Public
License along with this program; if not, write to the Free
Software Foundation, Inc., 675 Mass Ave, Cambridge, MA
02139, USA.

=head1 AUTHOR

Tobias Oetiker E<lt>tobi@oetiker.chE<gt>

=cut