On Jun 4, 2010, at 3:45 AM, David Schmitt wrote:
Hi all,
a recurring problem with the namevars are resources that do not have
a natural unique single-property key. For example, mysql users are
defined by their username and the host(-pattern) they are connection
from.
Traditionally, this was solved by ugly hackery in the type. In the
windows session at the puppetcamp, Markus and I developed the idea
of associating a set of patterns/syntaxes with the namevar to
automatically parse such multi-key titles and automatically put them
into proper parameters, which can then be validated, munged and used
without needing to know about the actual syntax elsewhere in the
type/provider.
It's definitely long-past time to solve this, and I'm glad it's
finally being worked on.
I'll start with an example, of how this could look like:
Puppet::Type.newtype(:mysql_user) do
@doc = "Manage a mysql database user."
ensurable
newtitle do
pattern "([...@]+)@([...@]+)", :user, :host
pattern "([...@]+)", :user
end
newparam(:user) do
desc "The username."
end
newparam(:host) do
desc "The host, the users connects from. This may be a pattern
using '%' and '_'."
defaultto "%"
end
Patterns would be tried in order and match groups assigned to the
specified parameters. Having no pattern match woul
This could be used in the following ways:
mysql_user {
"foo": ;
"f...@%": ; # both 'f...@%'
"bar": host => "localhost";
"b...@localhost": ; # both 'b...@localhost'
}
Mysql_user { host => "webserver" }
mysql_user { [ "frob", "frub" ]: }
# expands to 'f...@webserver' and 'f...@webserver'
mysql_user {
"frob": host => "web1";
"frob": host => "web2";
"frob": host => "web3";
}
What's the reason for not just requiring full parameter specification,
rather than supporting the title short-hand?
It seems to me we kind of have two problems: How to uniquely specify
the resource with parameters, and how to specify it with a resource
reference. Your solution (the title becomes a template filled in by
the different parameters) does kind of neatly solve it, but I'm afraid
it might be too complicated for normal humans to use.
The last stanza shows how this can be used to confusing effects.
This could be mitigated by allowing using arrays in parameters. For
example creating four users:
mysql_user {
[ "frob", "frub" ]:
host => [ "web1", "web2" ]
}
Here are some illegal constructs:
# Setting a property twice
mysql_user {
"foo": user => "bar";
"f...@%": host => "localhost";
}
# redefine resources
mysql_user {
"frob": ;
"f...@%": ;
"foo": host => "localhost";
"f...@localhost": ;
}
# pattern match fails:
mysql_user {
[ "", "@", "foo@", "@localhost", "f...@bar@localhost" ]: ;
}
For more flexibility when parsing, the list-of-paramnames could be
replaced by blocks:
pattern "complicated_regexp" do
# insert disgusting hack here
end
The block would have to return true or false to accept or reject the
title.
By substituting the param names into the patterns, puppet could
automatically create documentation like this:
Patterns:
1) u...@host:
user must be [...@]+
host must be [...@]+
2) user:
user must be [...@]+
user: The username.
host: The host, the users connects from. This may be a pattern using
'%' and '_'.
This could be enhanced by specifying additional docstrings with the
patterns.
Of course, this is currently vapour-ware, as it'll need some changes
in the puppet core to handle the new uniqueness, but I hope to
accelerate the development by providing a good spec/discussion of
how the "user-facing" side should look like.
It'd probably be a good idea to run through three or four other
resource types with this to see how it works. E.g., ports (/etc/
services), packages (optionally specify a version number or
architecture, where two packages with the same name but different
version/arch are considered different packages depending on the
provider, I think), and probably something else.
--
Trying to determine what is going on in the world by reading
newspapers is like trying to tell the time by watching the second
hand of a clock. --Ben Hecht
---------------------------------------------------------------------
Luke Kanies -|- http://puppetlabs.com -|- +1(615)594-8199
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