[Nagios-devel] Undefined behavior when processing multiple use statements

[Scott S. <ssa...@ta...>]

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Nagios clearly defines how it handles multiple inheritance when more
than one named object is included by 'use'. However, it does not
clearly define what happens when multiple use statements are present
in the object.

The definitions:

define host {
    host_name  host001
    use        env-dev,class-server,role-webserver
}

define host {
    host_name  host002
    use        env-dev
    use        class-server
    use        role-webserver
}

The two hosts appear to be identical, however the host templates are
inherited in different orders. Host001 will include the templates
env-dev, class-server, and role-webserver and will apply them in order
such that the env-dev template has precedence over the class-server,
and class-server will have precedence over role-webserver. However,
host002, applies precedence in the opposite order. Each use statement
seems to be evaluated independent of the others, in descending order.
This results in a precedence order of role-webserver, class-server,
env-dev.

I'm unsure if this is intentional or not, and the documentation does
not address objects containing multiple use statements. In my mind, it
makes sense for Nagios to treat the two definitions above as identical
since they appear syntactically identical. I expect Nagios to collect
all use statements and concatenate their values, then loop over the
comma separated values applying the templates as they are found.
Changing this behavior will affect backwards compatibility, but only
for an undocumented feature. I propose that this configuration syntax
is either documented as it currently exists, forbidden during the
runtime configuration check, or fixed to reflect the expected behavior.

Comments?

- -- 
Scott Sanders <ssa...@ta...>
Systems Administrator
TaxiMagic (http://taximagic.com)
office: 703-579-6818
mobile: 803-767-0060
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