[Xymon] Regional Servers to Central

[Thomas Eckert]

> On 03 May 2016, at 08:46, Adam Goryachev <mailinglists at websitemanagers.com.au> wrote:
> 
> On 03/05/16 12:02, Jeremy Laidman wrote:
>> On Sun, Apr 24, 2016 at 5:44 PM Thomas Eckert <thomas.eckert at it-eckert.de <mailto:thomas.eckert at it-eckert.de>> wrote:
>> Galen,
>> 
>> if egress SSH is allowed you could use an SSH tunnel from the central to the regional Servers opening say port 1985. Then use that for the communication between the Xymon servers.
>> 
>> This will weaken the intentions of the security policy of course ...
>> 
>> The tunnel can be managed by the ssh-tunnels extension by Padraig Lennon (on Xymonton) or my slightly extended version (on http://www.it-eckert.com/software/patches/ssh-tunnel/ <http://www.it-eckert.com/software/patches/ssh-tunnel/>). There are also some blog posts on my site on setup and combining with xymonproxy.
>> 
>> Sorry to be so late to the scene.  I have a similar requirement, but don't quite get the proposed solutions.  I have a couple of headless "probe" Xymon servers located on less trusted networks, and a pair of Xymon servers that primarily probe devices (testing TCP services, ping checks etc) on our internal network.  I want to be able to view the results of the probe servers on the internal server screens.  I can't have the probe servers connect inbound to the internal Xymon servers, except perhaps via ssh tunnel.
>> 
>> JC suggested that xymonfetch could be run on the regional (probe) servers to send in to the internal servers.  I haven't used xymonfetch before, so I'm not intimately familiar with how it's used.  Nevertheless, in reading the documentation I can see that xymonfetch is intended to run on a Xymon server to connect to a Xymon client that has msgcache running.  This doesn't seem to be the model described by JC, where msgcache isn't mentioned.  Or am I misunderstanding something?
>> 
>> Perhaps relevant to a solution, the Xymon probe servers periodically connect to the Xymon clients over ssh, create a reverse tunnel, and run xymonclient.sh with suitable environment variables to push the client data through the reverse tunnel.
>> 
>> Perhaps what I need to do is something like this.  I fire up a msgcache on each probe server, having everything feed into the msgcache instead of xymond, and I periodically run xymonfetch on each probe server to push the messages into the real xymond running there.  (I'd probably have xymond listen on an alternative port, and have msgcache run on 1984.)  I would then have the ability to run a second instance of xymonfetch on the probe servers, but being called via ssh from each internal server, complete with a reverse tunnel, so that the xymonfetch would inject into the xymond on the internal server.  What I can't figure out here is how to allow a msgcache queue to be pushed into the probe server's xymond without being emptied and hence unavailable for the internal xymon server.
>> 
> 
> 
> I would guess you can pass messages to xymonproxy, which will pass messages to the local xymon server plus xymonmsgcache, then the remote server will connect with ssh and collect the pending messages from the xymonmsgcache?
> 
> I hope that is what you were asking about.

I’ve only used `msgcache` on a single client up to now (for isolated hosts).
But I _seem_ to remember that there are limits on the amount of messages it can cache (beside other drawbacks, listed here <http://www.it-eckert.com/blog/2014/remote-site-monitoring-with-ssh-tunnel/ <http://www.it-eckert.com/blog/2014/remote-site-monitoring-with-ssh-tunnel/>>).

As I understand the intended use is

Xymon (central) — Xymon (region1) — multiple clients region1
                          |
                          — Xymon (region2) — multiple clients region2
                          |
                          — … 

This would lead to a potential huge number of messages on the regional Xymon servers that might well go beyond the capacity of `msgcache`.

Using `xymonproxy` on the regional servers would allow to deliver the status-messages to the (local) regional server _and_ the central one.
This is outlined here <http://www.it-eckert.com/blog/2014/combine-ssh-tunnel-with-xymonproxy/ <http://www.it-eckert.com/blog/2014/combine-ssh-tunnel-with-xymonproxy/>> (the "remote-datacenter” would be a regional server). To have the data available on the regional server as well the `xymond` there has to listen on say `127.0.0.1:1986` and xymonproxy report to that location as well (xymonproxy-option for sending to multiple servers `--server=SERVERIP[:PORT][,SERVER2IP[:PORT]]` — according to `xymonproxy(8)` up to 3 servers are possible, configuration it pulled from the _last_ in the list!). The order of the xymonproxy “receivers” would also allow the configuration of the regions to be either from central or from the regional server.

This setup is completely transparent to the client, the data they send and how (either directly, via ssh reverse-tunnel, …) as the xymonproxy listens on 1984 on the regional servers and “just takes care” to distribute the data.
The ssh-tunnel is handled by the central server using the `ssh-tunnel` extension (either original <https://wiki.xymonton.org/doku.php/addons:ssh_tunnel <https://wiki.xymonton.org/doku.php/addons:ssh_tunnel>> or extended version <http://www.it-eckert.com/software/patches/ssh-tunnel/ <http://www.it-eckert.com/software/patches/ssh-tunnel/>>) that takes care the tunnel is up.

All this only works out if the ssh-tunnels — initiated from central to regionals — is an option in your specific environment (mostly a question of security policy) of course. To sweeten the ssh-tunnel approach it should be noted that

- the msgcache solution would send the messages in clear-text — potentially exposing sensitive information.
- it allows to compress the data (with all the benefits for latency and bandwidth consumption).

Thomas

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