Allow the getval task to work with customized hostnames

[smortex]

Pull Request (PR) description

The default hostname used by collectd is system dependent as retuned by
gethostname(3) (On FreeBSD it's the FQDN, while on Linux it's the
non-FQDN). The python method socket.gethostname() always return a
non-FQDN, and the user has the ability to tune the hostname as he wish
in the collectd configuration (hostname parameter).

This change allow to use a customized hostname by using an optional
argument "hostname". When not provided, the non-FQDN and the FQDN are
tried in turn to fetch the requested metric value.

This Pull Request (PR) fixes the following issues

n/a

[traylenator]

Hi
There's example and parameters in README that could be extended with the new option.

[traylenator]

Glad someone using this, I pretty much did it as an academic exercise

[traylenator]

Rather than passing the hostname which will be different for every host can something be done with a fact name. Pass a factname and then that be used.
Trouble is I can't remember much how this stuff works.

[smortex]

Ah yes, didn't thing that passing the hostname does not scale beyond 1 node… Maybe we can just use hostname, and fallback to fqdn (so no custom values). We can also look for a setting in /etc/collectd/collectd.conf before falling back but some systems will use e.g. /usr/local/etc/collectd/collectd.conf…

Not ideal… What do you think ?

[traylenator]

Parsing collectd.conf seems a bit yuck.

We use:

FQDNLookup true

Sending a fact name of choice as a parameter then the user can specify if they
want networking.fqdn or networking.hostname

[traylenator]

I never realised you do a getval without the hostname.

collectdctl getval ai-catalog-diff/gauge-return_code

works perfectly well, that's the solution.

[smortex]

I never realised you do a getval without the hostname.

Interesting, I do not see this behavior and was thinking about contributing it maybe… A patch might be already available somewhere. On what system do you experience this?

[traylenator]

rpm -q collectd
collectd-5.8.1-1.el7.cern8.x86_64

Don't think we have any patches in this area.

We do have:

FQDNLookup true

I wonder if your $(hostname) is not equaul to $(hostname -f) ?