Steve Kemp's Blog Writings relating to Debian & Free Software

So slaughter is definitely getting overhauled

Wed, 24 Oct 2012 12:32:38 GMT

There have been a few interesting discussions going on in parallel about my slaughter sysadmin tool.

I've now decided there will be a 2.0 release, and that will change things for the better. At the moment there are two main parts to the system:

Downloading polices

These are instructions/perl code that are applied to the local host.

Downloading files

Polices are allowed to download files. e.g. /etc/ssh/sshd_config templates, etc.

Both these occur over HTTP fetches (SSL may be used), and there is a different root for the two trees. For example you can see the two public examples I have here:

A fetch of the policy "foo.policy" uses the first prefix, and a fetch of the file "bar" uses the latter prefix. (In actual live usage I use a restricted location because I figured I might end up storing sensitive things, though I suspect I don't.)

The plan is to update the configuration file to read something like this:

transport = http

#
# Valid options will be
#    rsync | http | git | mercurial | ftp
#

#
# each transport will have a different prefix
#
prefix = http://static.steve.org.uk/private

# for rsync:
#  prefix=rsync.example.com::module/
#
# for ftp:
#  prefix=ftp://ftp.example.com/pub/
#
#  for git:
#  prefix=git://github.com/user/repo.git
#
#  for mercurial
#  prefix=http://repo.example.com/path/to/repo
#

I anticipate that the HTTP transport will continue to work the way it currently does. The other transports will clone/fetch the appropriate resource recursively to a local directory - say /var/cache/slaughter. So the complete archive of files/policies will be available locally.

The HTTP transport will continue to work the same way with regard to file fetching, i.e. fetching them remotely on-demand. For all other transports the "remote" file being copied will be pulled from the local cache.

So assuming this:

transport = rsync
prefix    = rsync.company.com::module/

Then the following policy will result in the expected action:

if ( UserExists( User => "skx" ) )
{
    # copy
    FetchFile(
            Source => "/global-keys",
              Dest => "/home/skx/.ssh/authorized_keys2",
             Owner => "skx",
             Group => "skx",
              Mode => "600" );
}

The file "/global-keys" will refer to /var/cache/slaughter/global-keys which will have been already downloaded.

I see zero downside to this approach; it allows HTTP stuff to continue to work as it did before, and it allows more flexibility. We can benefit from knowing that the remote policies are untampered with, for example, via the checking built into git/mercurial, and the speed gains of rsync.

There will also be an optional verification stage. So the code will roughly go like this:

  • 1. Fetch the policy using the specified transport.
  • 2. (Optionally) run some local command to verify the local policies.
  • 3. Execute policies.

I'm not anticipating additional changes, but I'm open to persuasion.

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