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 endend...<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 endend
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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