attributes_server.rb

set_unless[:rabbitmq][:flow_control_watermark] = 0.6
set[:rabbitmq][:cluster] = [
    # Each list of hostnames defines a cluster.
    [
        'mq3.internal.sazze.com',
        'mq4.internal.sazze.com'
    ],
    [
        'mq5.internal.sazze.com',
        'mq6.internal.sazze.com'
    ]
]

recipes_server.rb

cluster_nodes = []

node[:rabbitmq][:cluster].each do |cluster|
    
    if cluster.include?(node[:fqdn])
        cluster_nodes += cluster.reject { |item| item == node[:fqdn] }
        break
    end
end

template "rabbitmq.config" do
    path "/etc/rabbitmq/rabbitmq.config"
    source "rabbitmq.config.erb"

    mode 0644
    owner "root"
    group "root"
    
    action :create
    
    variables(
        :vm_memory_high_watermark => node[:rabbitmq][:flow_control_watermark],
        :cluster_nodes => cluster_nodes.join("', 'rabbit@")
    )
end

template_rabbitmq.config.erb

[
    {
        rabbit, [
            {vm_memory_high_watermark, <%= @vm_memory_high_watermark %>},
            <% unless @cluster_nodes.empty? -%>
            {cluster_nodes, ['rabbit@<%= @cluster_nodes %>']}
            <% end -%>
        ]
    }
].