[chef] Concurrency node creation issue

[Daniel Cukier < >]

Hi,

I have in my infrastructure a topology where there's one master node and many slave nodes.

What I want to do is to automatically detect if a node is a master or a slave. The rule is:

 1) If there is no master node yet, the next node will be the master

 2) If there is a master, the next node will be slave and its master will be the already existing master.

The problem occurs when I have an empty infrastructure (zero nodes) and I try to create the first 2 nodes simultaneously.

When both nodes get provisioned, both check that there is no master and both are set to be master, which is a wrong configuration.

This is a very common synchronization problem, but I don't know how to deal with it in the Chef environment. 

Here's the recipe to configure a node:

@@master = node

search(:node, 'role:myrole') do |n|

  if n['myrole']['container_type'] == "master"

    @@master = n

    if n.name != node.name

      node.set['myrole']['container_type'] = "slave"

    end

  end

end

if @@master == node

  node.set['myrole']['container_type'] = "master"

end

template "#{node['myrole']['install_dir']}/#{ZIP_FILE.gsub('.zip', '')}/conf/topology.xml" do

  source "topology.xml.erb"

  owner "root"

  group "root"

  mode "0644"

  variables({:master => @@master})

end

How can I avoid this problem? 

Thanks a lot

Daniel Cukier