[Pacemaker] Enable remote monitoring

[Arnold Krille]

On Monday 12 November 2012 10:50:57 Dejan Muhamedagic wrote:
> Hi Arnold,
> 
> On Sun, Nov 11, 2012 at 07:37:29PM +0100, Arnold Krille wrote:
> > On Sun, 11 Nov 2012 18:37:04 +0100 Dejan Muhamedagic
> > 
> > <dejanmm at fastmail.fm> wrote:
> > > On Fri, Nov 09, 2012 at 05:22:08PM +0100, Lars Marowsky-Bree wrote:
> > > > On 2012-11-09T14:06:29, Dejan Muhamedagic <dejanmm at fastmail.fm>
> > > > 
> > > > wrote:
> > > > > > And also doesn't really help with getting the state/readiness of
> > > > > > services the guest might provide.
> > > > > 
> > > > > Isn't it that one gets a login prompt only once the host reached a
> > > > > certain run level?
> > > > 
> > > > Services may start in the background. The console may either be
> > > > text, graphical, or network only.
> > > 
> > > Hmm, I have yet to see a Linux/UNIX host without a console. And
> > > that means quite some time ;-)
> > 
> > While (almost) all systems have some kind of console, not all systems
> > stay at a text-console during runtime.
> 
> It seems like you are mixing things up. This is not about
> watching a computer monitor. On Linux there's always a console
> tty.

1) There are linux systems without a tty.
2) Watching the first / whatever tty is not telling you anything. Some systems 
don't run a login on tty1 but show tty1 after start, some systems switch to 
graphics (yes, virtual machines do that too), some machines show a nice menu 
letting you choose your language and stuff.

> > If you want to watch  a
> > linux-terminal-server, its not a text-console that is the primary
> > screen.
> > 
> > And then watching the text-console for a login:-prompt tells you that
> > the machine is up. "Pressing" enter tells you that the login-process is
> > still answering. But that doesn't tell you whether the webserver on
> > that machine is still working correctly.
> 
> That is not the point.
> 
> > Its not even telling you if
> > the machine is reacting to network stuff. All it tells you is that some
> > kind of system is started. So its actually only a little more then
> > "virsh list |grep <machinename>" tells you.
> > 
> > Imho watching the console for monitoring a machine is as useless as it
> > can get.
> 
> It tells you that a host is at a certain runlevel. The host is
> ready for business, i.e. all other service at the particular
> runlevel have been started. Otherwise, it wouldn't make sense
> that it offers a login prompt. I don't know how it is with
> systemd, perhaps systemd functions differently. Whether a
> particular service is functioning properly or at all is up to the
> monitor resource to find out.

Watching the/a tty of a linux machine is not telling you anything in general. 
It's only us humans that can make some sense of what we see there. For a 
machine to watch another generic machine via tty its to much variables and to 
much engineering needed.

BTW: Some machines present the login:-prompt (text and graphics) well before 
everything is started, suse and ubuntu did that some three-five years ago 
already.

And actually I don't care (cluster-wise) at which runlevel the webserver is, 
it has to serve pages at port [80,443] otherwise its useless and has to be 
killed and restartet. No monitoring of any tty can tell me that...

Have fun,

Arnold
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