Puppet 2.7.x - Global variable - Append

Without getting to far into the weeds, Nginx is forcing my hand in order to accomplish some magic with vhosts and the map directive.

Is there an elegant (relative) solution to sharing a variable across multiple define calls, which allows each define call to append it's data to the global variable? In software this would be known as a singleton.

-- The weeds --

Nginx has a map directive which dictates which upstream server pool the request should be passed to, like so:

map $http_host $upstream_pool {

    hostnames;

    blog.example.com     blog_example_com;
    repo.example.com     repo_example_com;

    default example_com;
}

As you can see, any requests for blog.example.com will be passed to the blog_example_com upstream server pool (by way of proxy_pass).

The problem is the map directive syntax is that it can only be included within the main http block (nginx.conf), whereas vhost specific directives such as upstream and location can be included in the server block of a vhost config.

My nodes.pp manifest looks something like this:

 service-a-1.example.com inherits project_dev {

     nginx::vhost { 'mothership': }
     nginx::vhost { 'mothership_blog': }
     nginx::vhost { 'repo': }
}

As you can see, after a successful puppet run, I should end up with 3 distinct vhost config files in /etc/nginx/vhost.d/ dir.

The problem I am having is that in order for the map directive to work, I need to know which vhosts were loaded, so I can add their respective upstream ids to the map directive, which I have defined in the primary config: /etc/nginx/nginx.conf within the http block (of which there can only be one).

-- What I have tried --

I have a global.pp file which does some "bootstrapping" and in this file I added a $singleton = '' syntax, then in the nginx::vhost define, I added this syntax:

$tpl_upstream_pool_labels = inline_template("<% tpl_upstream_pools.keys.sort.each do |role| %><%= role %>_<%= tpl_domain_primary %>_<%= tpl_domain_top_level %>|<% end %>")

$singleton = "${singleton}${tpl_upstream_pool_labels}"

notify { "\n--------------------- Nginx::Conf::Vhost::Touch | Timestamp: ${timestamp} | Pool labels: ${singleton} -------------------------\n": }

Which should result in a pipe delimited list of upstream ids. As mentioned earlier, in the nodes.pp manifest, I make three calls to nginx::vhost, and would expect the $singleton global variable to be appended for every call, however it is not, it only contains the last call's data.

I also tried to hack my way around this by writing a temp file like so:

$temp_file_upstream_pool_labels_uri = "/tmp/puppet_known_upstreams_${timestamp}.txt"

exec { "event_record_known_upstream_${name}" :            
    command     => "touch ${temp_file_upstream_pool_labels_uri} && echo ${tpl_upstream_pool_labels} >> ${temp_file_upstream_pool_labels_uri}",            
    provider    => 'shell'
}

Then in the nginx::conf::touch define, where the primary config nginx.conf is to be written by puppet, I tried this:

$temp_file_upstream_pool_labels_uri = "/tmp/puppet_known_upstreams_${timestamp}.txt"

$contents = file($temp_file_upstream_pool_labels_uri)

Which should, in theory, load the contents of the file into the $contents variable. But when I run puppet using this approach I get an error that the file does not exist. I ensured that the nginx::conf::touch call is not made until after all the vhosts were considered, but still to no avail.