I haven't seen this really discussed in the wiki or on the list. I
suspect anyone with enough knowledge to help me can already tell where
I'm going from the subject, but here's a lengthy description of the
problem anyway…
For files like sshd_config or Postfix's main.cf, using Augeas is very
straightforward. You have a bunch of unique keys, you set the values
for the ones you care about, Puppet can tell what does and does not
need to be changed and you get on with your life.
However, what seems like a majority of files are broken up into an
"array" of values. Take the `/etc/exports` [example from the wiki][1].
Existing items are assigned numbers 1-4 by Augeas when the file is
loaded. If you add an item with an index of 10000, the tree will
contain items 1, 2, 3, 4 and 10000 until you save the changes. But on
the next Puppet run, Augeas will load the file and number the items
1-5. There won't be an item 10000, so what's to stop it from being
added over and over again on every run? The same can be said for
inserting things. Say I want to insert something after /2 in `/etc/
inittab`. There will be a /2 in the tree on every single run, so
what's to stop it from inserting again and again?
I guess what I'm getting at is that the Augeas type seems extremely
whatever-the-opposite-of-idempotent-is by default. Or at least it's
very easy for a person to accidentally make a mess.
I realize the numbering of items in certain files is unavoidable, but
is there a good way to handle these situations in Puppet? Here are
some real-world examples from my manifests that seem to work.
# 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",
}
This inserts a line after the `/etc/rc.d/rc.sysinit` line. Works fine
now, but what if the sysinit line isn't item 2 in every future version
of the OS? Maybe I could add "only if 2's id is 'si'" to make sure,
but what if it's *not* 'si'? It won't get added to the wrong place,
but it won't get added anywhere else either. Clearly not what I'm
shooting for.
# boot systems to runlevel 3
augeas { "runlevel":
context => "/files",
changes => [
"set /etc/inittab/1/runlevels 3",
],
onlyif => "get /etc/inittab/1/action == initdefault",
}
Again, this works, but what if initdefault was *not* item 1? I've
prevented the wrong thing from happening, but I haven't ensured the
right thing. (By the way, why are items numbered in inittab when they
all have an "id"?)
On a related note, there doesn't seem to be a good way to add comments
to a particular spot to explain the changes you've made. This is true
even for the "straightforward" files mentioned above. Any advice?
Please view this as a question and not a complaint. If I didn't think
Augeas and its Puppet type were awesome, I wouldn't have tried to use
them heavily enough to encounter the above. Thanks.
[1]: http://reductivelabs.com/trac/puppet/wiki/PuppetAugeas
--
Rob McBroom
<http://www.skurfer.com/>
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