Can't pass in vars from a recipe to a template and get them evaluated late enough.

recipe.rb

ruby_block "set_read_and_write_limits" do
  block do
    raidable_disks = []
    node["ec2"].each do |k, v|
      if (k =~ /^block_device_mapping_ephemeral/)
        dev_name = "/dev/" + v.sub('sd', "xvd")
        if File.exist?(dev_name)
          raidable_disks << dev_name
        end
      end
    end
    # Recommendation from Palomino for ec2:
    # Concurrent reads: 16 * <# of drives in an array>
    # Concurrent writes: 8 * <# of cores>
    reads          = 16 * raidable_disks.length
    writes         =  8 * node["cpu"]["total"].to_i
    throttle_limit =  2 * (reads + writes)
    Chef::Log.warn("concurrent_reads: #{reads} concurent_writes: #{writes} throttle_limit: #{throttle_limit}")
    node.set["cassandra"]["concurrent_reads"]  = reads
    node.set["cassandra"]["concurrent_writes"] = writes
    node.set["cassandra"]["throttle_limit"]    = throttle_limit
    # 2x (concurrent_reads + concurrent_writes)
  end
end
# ...
template "#{node["cassandra"]["conf_dir"]}/cassandra.yaml" do
  source        "cassandra.yaml.erb"
  owner         "root"
  group         "root"
  mode          "0644"
  variables     ( {
                    :cassandra => node["cassandra"]
                  } )
  notifies      :restart, "service[cassandra]"
end

reverts_to_defaults.erb

# ...

# Unlike most systems, in Cassandra writes are faster than reads, so
# you can afford more of those in parallel.  A good rule of thumb is 2
# concurrent reads per processor core.  Increase ConcurrentWrites to
# the number of clients writing at once if you enable CommitLogSync +
# CommitLogSyncDelay. -->
concurrent_reads: <%= @cassandra["concurrent_reads"] %> #8
concurrent_writes: <%= @cassandra["concurrent_writes"] %> #32
# ...

working.erb

# ...

# Unlike most systems, in Cassandra writes are faster than reads, so
# you can afford more of those in parallel.  A good rule of thumb is 2
# concurrent reads per processor core.  Increase ConcurrentWrites to
# the number of clients writing at once if you enable CommitLogSync +
# CommitLogSyncDelay. -->
concurrent_reads: <%= node["cassandra"]["concurrent_reads"] %> #8
concurrent_writes: <%= node["cassandra"]["concurrent_writes"] %> #32
# ...