Re: Maintaining RC symlinks

[Luke A. Kanies]

On Wed, 9 Jun 2004, Chip Seraphine wrote:

> To provide a baseline, here is what I am currently doing:
>
> groups:
>        has_mysql_runlinks=      ( IsLink(/etc/rc3.d/S90mysql)
>                                   IsLink(/etc/rc5.d/S90mysql) )

I don't know how much you've tested this, but it is highly unlikely that 
this is doing what you think it is.

Cfengine parses the above line as two separate values for 
'has_mysql_runlinks', which means that the last value ends up being the 
real value.  It doesn't matter what the results of any other IsLink() 
calls are.  I just verified this.

If you want the test to work as (I think you) expect, you need to AND 
those IsLink() calls:

groups:
        has_mysql_runlinks = (
                IsLink(/etc/rc3.d/S90mysql).IsLink(/etc/rc5.d/S90mysql)
        )

> links:
>         mysqlserver::
>                 /etc/rc3.d/S90mysql     -> ../init.d/mysql
>                 /etc/rc5.d/S90mysql     -> ../init.d/mysql
>
> shellcomamnds:
>         !mysqlserver.has_mysql_runlinks::
>                 "/bin/rm -f /etc/rc*.d/S90mysql"
>
>
> This method is rather clunky (editing 3 seperate sections) and inefficient
> (every host stats for two symlinks every run).

Ayup, although it's the maintenance clunkliness I'd be worried about, not 
the stat'ing.  I don't expect there's much you can do about that.

> Here is what (unless somebody has a better, more cfenginey way) I intend to
> do:
>
> groups:
>         mysqlserver=            ( dbhost1 dbhost2 )
>         service_mysqlserver=    ( mysqlserver )
>
> shellcommands:
>         "/var/cfengine/bin/cfservice '$(allclasses)'"
>
>
> ... and the cfservice script will detect the 'service_mysqlserver' script and
> Do The Right Thing (which will probably be running chkconfig on Linux hosts,
> or explicitly setting/removing links on others)  for every service (i.e.
> script in init.d) that does or does not have a corresponding service_* class
> defined.
>
> The second approach is nonconvergent and requires me to write Yet Another
> External Script, so I find it only marginally preferable to the first one.
> Anybody out there has something better?

Hmm.  I keep recommending this and everyone keeps ignoring me, so feel 
free to do so, but....

I _would_ write an external script, but it would be very simple.  Maintain 
a mapping between classes (e.g., mysqlserver) and appropriate runlevel 
options:

$VAR1 = {
  "mysqlserver" => {
     "K" => 10,
     "S" => 90,
  },
};

Your external script reads in that mapping, and then just loops across 
each class:

# no, i don't expect this all to work on first try
# all written off the top of my head
# mmmm, ruby....
my $linkcode = "links:
";

my $rmcode = "disable:
";

my %classes;
foreach my $class ((split /:/, $ENV{'CFALLCLASSES'}) {
  $classes{$class}++;
}

# for every class we're looking at, make sure 1) we're that class, or
# 2) we don't have the startup scripts there
foreach my $class (keys %$VAR1) {
  if ($classes{$class}) {
    my $k = $VAR1->{$class}->{"K"};
    my $s = $VAR1->{$class}->{"S"};
    $linkcode .= "\t/etc/rc2.d/$s$class -> ../init.d/$class\n";
    $linkcode .= "\t/etc/rc0.d/$k$class -> ../init.d/$class\n";
    $linkcode .= "\t/etc/rc6.d/$k$class -> ../init.d/$class\n";
  } else {
    $rmcode .= "/etc/rc2.d/$s$class";
    $rmcode .= "/etc/rc2.d/$s$class";
    $rmcode .= "/etc/rc2.d/$s$class";
  }
}

Then just execute the $linkcode and $rmcode, either through importing it 
in a later run or just executing immediately.

No, it's not exactly trivial, but once you've got the (actually quite 
simple) external script written it is trivial to maintain, and all you 
really ever modify is the mapping file (which I normally store in 
/var/cfengine/data).  It's totally convergent (because you're actually 
using cfengine to do the work), and it's not that hard to support multiple 
platforms (change the paths or whatever).

I generally also make these modules, but that's just me.

Luke

--
Yesterday upon the stair
I met a man who wasn't there.
He wasn't there again today --
I think he's from the CIA.
---------------------------------------------------------------------
Luke Kanies | http://abstractive.org | http://reductiveconsulting.com