gistfile1.rb

entries.each do |e|
  begin
    do_stuff(e)
  rescue => error
    $redis.lpush("failed_strip", e.id) # will create the list and/or append the value
end

# counting
puts "failed: " + $redis.llen("failed_strip")

# using
ids = $redis.lrange("failed_strip", 0, -1)
Foo.where(id: ids).each do |e|
  retry_do_stuff(e)
end