[chef] race condition in the postgresql::ruby recipe

[Bryan Berry < >]

Dear Chefs and esp. Jesse H,

I have encountered in another race condition in the postgresql::ruby recipe. This recipe installs the pg gem which depends on the postgresql-devel package. It is installed as a chef_gem which means it runs immediately at compile time. This is problematic since it depends on the resource that installs the postgresql-devel package. The current recipe gets around this by forcing that package to install immediately before processing the chef_gem resource.

This is problematic for me as I use another resource to configure the yum repository for postgresql. The current postgresql::ruby recipe fails for me as the postgresql repository is not yet configured. The postgresql90-devel package can't be found. I would have monkey patch that resource to run immediately prior to installing postgresql-devel. 

I have an alternate solution that I have submitted as a patch

https://github.com/opscode-cookbooks/postgresql/pull/11

There is a little extra weirdness here as the recipe fails for me if `pg_config` binary isn't in the PATH

Rather than running a bunc of resources at compile-time, I chain them using my hacky check for the existence of a package + the subscribes attribute. 

pg_devel_pkg = node['postgresql']['client']['packages'].select { |pkg| pkg =~ /devel/ }.first
pg_devel_status = Chef::ShellOut.new("rpm -qa #{pg_devel_pkg}").run_command.stdout
pg_devel_installed = ! pg_devel_status.empty?


link "/usr/bin/pg_config" do
  to "/usr/pgsql-#{node['postgresql']['version']}/bin/pg_config"
  unless pg_devel_installed
    action :nothing
    subscribes :create, resources("package[#{pg_devel_pkg}]"), :immediately
  else
    action :create
  end
end


chef_gem "pg" do
  if ::File.exists? "/usr/bin/pg_config"
    action :install
  else
    action :nothing
    subscribes :install, resources("link[/usr/bin/pg_config]"), :immediately
  end
end




The first 3 lines here could be generically encapsulated as a function like `Package.installed? "postgresql-devel"`  such a method could be immensely useful


This patch fixes my problems on Centos 6.3 but I have not tested on any other platform. Is my use of the hacky Package.installed?  + subscribes a good idea?


I keep running into issues w/ cookbooks that push the execution of resources into compile-time. This strategy is really fragile in my humble opinion. We need to find a better way to handle such run-time dependencies.