This script finds dead/zombied nodes and clients on your chef server and removes them. Note: I pulled this from a larger script so it probably needs some bandaids.

reap.rb

require 'fog'
require 'json'
require 'pp'
require 'chef'

connection = Fog::Compute.new(
      :aws_access_key_id => #insert id here,
      :aws_secret_access_key => #insert secret here,
      :provider => 'AWS'
    )

env = Chef::Config
env[:node_name] = "<username>"
env[:client_key] = "<user.pem>"
env[:validation_key] = "<validation.pem>"
env[:validation_client_name] = "chef-validator"
env[:chef_server_url] = "http://<chef server>:4000"
      
aws_instance_ids = []
instance_data = connection.describe_instances

instance_data[:body]["reservationSet"].each do |instance|
  id = instance["instancesSet"].first["instanceId"]
  aws_instance_ids.push(id)
end
      
nodes = Chef::Node.list(true)
puts "Chef Node start count: #{nodes.count}"

nodes.each do |node_name, node_obj|
  chef_instance_id = node_obj.attributes.automatic["ec2"]["instance_id"]
  if !aws_instance_ids.include?(chef_instance_id)
    print "#{node_name} does not exist in EC2 would you like to delete (y[es],n[o]) "
    response = STDIN.gets
    while(!["yes", "no", "y", "n"].include?(response.strip.downcase))
      print "Invalid yes or no "
      response = STDIN.gets
    end
    if ["yes", "y"].include?(response.strip.downcase)
      client = Chef::ApiClient.load(node_name)
      node_obj.destroy #delete node
      client.destroy   #delete client
    end
  end
end