This how-to will describe how to configure a "passive" poller that is located behind a NAT firewall where port forwarding is not possible. This is called running a passive poller. Running multiple poller nodes behind the very same NAT is not supported ? two nodes must not be seen at the same IP address, in the master's point of view.

Prerequisites
In this example we have a master server called master01 and a poller called nat_poller that is behind a firewall.

• The master server must be accessible on port 22 and 15551 from the poller.
• Basic understanding of op5 Monitor with master-peer configuration

Steps

1. On master01, edit the /etc/hosts file using your favorite text editor, and map the hostname nat_poller to the outgoing NAT IP address of nat_poller (i.e. the IP address which the poller will connect from in the master's point of view). Example:

   192.0.2.34 nat_poller

2. On master01, set up the poller node nat_poller by executing the command below.

   mon node add nat_poller type=poller hostgroup=nat_poller

3. On master01, edit the /opt/monitor/op5/merlin/merlin.conf configuration file, and insert takeover = no and connect = no into the nat_poller configuration block. Example:

   poller nat_poller {
       address = nat_poller
       port = 15551
       hostgroup = nat_poller
       connect = no
       takeover = no
   }      

4. On nat_poller, set up the master node master01 by executing the command below.

   mon node add master01 type=master

5. On nat_poller, edit the /opt/monitor/op5/merlin/merlin.conf configuration file, and insert into the master01 configuration block: a sub-block called object_config, containing fetch_name and fetch settings. Example:

   master master01 {
       address = master01
       port = 15551
       object_config {
           fetch_name = nat_poller
           fetch = mon oconf fetch master01
       }
   }      

   The value of the fetch_name setting should be set to the name of the poller.
    

6. On nat_poller, disable any default nagios object configuration files by executing the command below.

   sed -i /^cfg_file=/d /opt/monitor/etc/nagios.cfg

7. On nat_poller, verify and set up SSH connectivity by executing the command below.

   mon sshkey push --all

8. On master01, restart the op5 Monitor system services by executing the command below.

   mon restart

9. On nat_poller, fetch the new configuration from master01 by executing the command below.

   asmonitor mon oconf fetch master01