Open Stack

Hi all,

(I've been away for a couple of weeks and I tried to send this before I
left. I didn't see it come through so my apologies if this is the second
time you've seen this.)

I recall markvan mentioning a while ago that there was a need for services
to restart when the underlying package changed but the config file didn't.
We've got something in place and working that does exactly that. I'd like
to get y'all's opinion if it's an ugly kludge or something useful that we
might want to refine and contribute back.

The basic approach is to look up a given package's version at recipe compile
time, and then again at runtime.  If the two values are different, then we
notify the service to stop. We rely on the main recipe to make sure that
the service is started. This avoids multiple restarts if both the package
and the config change.

For example, we have a library module that contains a routine that does the
equivalent of 'rpm -q a <name>'.  If the package isn't installed yet, then
the library routine will just return an empty string and that'll be
different from the post install version.

In the recipe itself, we then have the following: (This is from our glance
recipe.)

# Get access to the library routine that can look up package
# versions. Note that we're including it twice. The first time is
# so that we can get the preinstall version during the compile phase.
# The second include is so that we can check the package version
# during the run-time phase. Yes, we could have done the preinstall check
# at run time and just had one include, but that rubyblock of code is
# more complicated than doing the include.
class ::Chef::Recipe # rubocop:disable Documentation,ClassAndModuleChildren
  include <our special module>
end

class ::Chef # rubocop:disable ClassAndModuleChildren
  class Resource
    class RubyBlock # rubocop:disable Documentation
      include <our special module>
    end
  end
end
...
<package install commands>
...
# trigger_pkg is the package that we want to check and was picked it up
# from an attribute. We'll call our library routine (this is at compile
# time) and stash the preinstall version.
node.default['openstack']['image']['preinstall'] =
  pkg_version(trigger_pkg)

# Check the installed version at runtime, after the pkg commands
# have actually run.  If there's a change in the version, then tell
# glance to shutdown. It'll get restarted later on and pick up the
# new binaries.
ruby_block 'glance postinstall' do
  block do
    postinstall_version = pkg_version(trigger_pkg)
    preinstall_version = node['openstack']['image']['preinstall']
    Chef::Log.info "preinstall version: #{preinstall_version}"
    Chef::Log.info "postinstall version:#{postinstall_version}"
    if preinstall_version != postinstall_version
      Chef::Log.info 'Stopping glance services'
      resources(service: 'glance-api').run_action(:stop)
      resources(service: 'glance-registry').run_action(:stop)
    else
      Chef::Log.info 'No need to stop glance services'
    end
  end
end


That's the basics. Is this worth pursuing? If it seems reasonable then I'll
be happy to write up a spec, including any suggestions y'all may have. I.e.
there may be some really braindead stuff in there just from my ignorance
and flailing around just to make it work. I'm definitely open to
suggestions.

Ken
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