On 2009-May-16, at 12:42 PM, Brent Chapman wrote:
> If your goal is to append something to an Augeas list, then I think
> it's much better to use the [last()+1] notation.
There are a couple of problems with that. Using last() is a better
method as far as general Augeas technique goes, but it doesn't address
the problem with using Augeas in Puppet. Also, the last() function
only seems to be available for labels with multiple values. It doesn't
seem to work for things like /etc/inittab or /etc/hosts where the
numbers assigned represent lines in the file. For instance:
augtool> ls /files/etc/inittab/last()
augtool> ls /files/etc/inittab/20
id = x
runlevels = 5
action = respawn
process = /etc/X11/prefdm -nodaemon
Here are a couple of examples to further illustrate what I'm trying to
avoid. First, something as simple as adding a host to /etc/hosts
(using 10 since last() isn't an option here):
augeas { "repeathost":
context => "/files/etc/hosts",
changes => [
"set 10/ipaddr 10.10.10.10",
"set 10/canonical foo",
"set 10/alias foo.localdomain",
]
}
This adds the same host on every puppet run until there are 10 hosts
total, at which point it compares the changes to the existing item 10,
sees that there is nothing to be done, and moves on (as it should).
The same happens if you use last() instead of an arbitrary high number:
augeas { "repeatalias":
context => "/files/etc/hosts",
changes => [
"set 4/ipaddr 10.10.10.10",
"set 4/canonical foo",
"set 4/alias foo.localdomain",
"set 4/alias[last()+1] bar.localdomain",
]
}
This will add the "bar" alias over and over on every puppet run until
the disk fills up or something else breaks.
I understand *why* this is happening. It just doesn't seem very Puppet-
like, so I wanted to make sure I'm not overlooking something. It seems
that to use the Augeas type, you have to explicitly tell it "unless
this has already been done" with nearly every augeas resource you
define. With user, file, yumrepo, package, and every other type of
resource I've worked with, you just tell it what you want to be true
and Puppet will determine if any action is required to make it happen.
If this is the way it is, then fine. Maybe it's not technically
feasible to make the augeas type figure this stuff out on its own. I
just want to confirm that before I put a lot of time into working
around this limitation.
> As for the second problem which Rob raises, that of making sure
> you're editing the section of an Augeas tree that you think you are,
> I'd again suggest that the problem is in using the Augeas index
> numbers directly. Rob gives the following example, to add a new 3rd
> line to /etc/inittab, which assumes that line 2 is the "/etc/rc.d/
> rc.sysinit" line:
>
> # adds rh:06:wait:/etc/rc.shutdown
> augeas { "shutdown":
> require => File["shutdown"],
> context => "/files/etc/inittab",
> changes => [
> "ins 3 after 2",
> "set 3[1]/id rh",
> "set 3[1]/runlevels 06",
> "set 3[1]/action wait",
> "set 3[1]/process /etc/rc.shutdown",
> ],
> onlyif => "get 3/id != rh",
> }
>
> What I'd suggest here is, instead of referring to the relevant
> entries by Augeas index number (which happens to correspond to line
> number, in this case), refer to them using the Augeas "path
> expressions" mechanism (http://augeas.net/page/Path_expressions).
I'll look into that.
> As a general practice, I'd say that you want to avoid explicitly
> using the "line number" indexes that Augeas generates when it loads
> a file.
Oh, I surely do. I just wasn't sure how. Looks like path expressions
will help in some situations.
Thanks again.
--
Rob McBroom
<http://www.skurfer.com/>
The magnitude of a problem does not affect its ownership.
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