On Thu, Sep 16, 2010 at 12:41 AM, <no-re...@cfengine.com> wrote:
> Forum: Cfengine Help
> Subject: Re: Cfengine Help: Looking for ideas on people's config
> Author: hhammer
> Link to topic: https://cfengine.com/forum/read.php?3,18246,18258#msg-18258
>
> Thanks. So in this example:
>
> ----
> "common_seq" slist => { "some", "common", "bundles" };
>
> web_servers::
> "site_seq" slist => { @(common_seq), "php", "apache2" } ;
>
> data_servers::
> "site_seq" slist => { @(common_seq), "mysql" } ;
>
> processing_servers::
> "site_seq" slist => { @(common_seq), "some_engine" } ;
> ----
>
> How does one compose a site_seq list for hosts that are web_servers and
> data_servers? Is adding a final line like
>
> web_servers.data_servers::
> "site_seq" slist => { @(common_seq), "php", "apache2", "mysql" } ;
>
> the only way? Or can we do something like
>
> ----
> "site_seq" slist => { "some", "common", "bundles" };
>
> web_servers::
> "site_seq" slist => { @(site_seq), "php", "apache2" } ;
>
> data_servers::
> "site_seq" slist => { @(site_seq), "mysql" } ;
>
> processing_servers::
> "site_seq" slist => { @(site_seq), "some_engine" } ;
> ----
>
> That would be cool, but cfengine doesn't seem to like it.
>
Wow you hit the nail on the head very quickly. I my opinion the inability to
extend an slist is cfengine greatest current weakness, one that undermines
it greatest strength (class based convergence). I think the notion of
convergence is great for my system state - not so great for variable
resolution. The solution I have had to construct every time I run into this
issue is to introduce another variable to handle the extra dimension, e.g.L
----
"common_seq" slist => { "some", "common", "bundles" };
"extra_seq" slist => { } ;
web_servers::
"locl_seq" slist => { "php", "apache2" } ;
data_servers::
"locl_seq" slist => { "mysql" } ;
processing_servers::
"locl_seq" slist => { "some_engine" } ;
data_servers.processing_servers::
"extra_seq" slist => { "something_else" } ;
----
and then:
"site_seq" slist => { @(common_seq), @(locl_seq), @(extra_seq) } ;
Actually even the above convolutions don't work (because you cant have
an empty slist) - and every time you introduce a new dimension you need to
introduce a new variable to cater for it. Sometimes I get sick of this, and
just start repeating sections of code, e.g.:
data_servers.processing_servers.SomeOtherDimension::
"extra_seq" slist => { "something_else", "some_other_bundle" } ; # because I
could not do: "extra_seq" slist => { @{extra_seq}, "some_other_bundle" } ;
The problem with the above is I have now had to write in two places that
'data_servers.processing_servers' include "something_else".
Have fun!
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