Redis lock implementation
Here's a stab at clarifying the intent without changing any of the functionality. I didn't try to run it or anything, so don't hold me to syntax. 

# handles locking and unlocking redis for a particular operation
class RedisLock
  # thrown when a lock cannot be acquired
  class NotAcquired &lt; StandardError; end

  # since the redis key and ms are used in pretty much every method,
  # might as well go ahead and pass them in the constructor.
  # set defaults here if there are defaults that make sense.
  # make a yardoc comment and describe what these all are.
  def initialize(redis: Redis.current, nx: true, redis_key:, expiration_ms:)
    @redis = redis
    @redis_key = redis_key
    @expiration_ms = expiration_ms
    @nx = nx
  end

  # call it with_lock instead of lock
  # to make it more apparent it accepts a block
  def with_lock!
    raise(NotAcquired, "Could not acquire lock with #{args}") unless lock
    yield
    unlock(redis_key, random_lock_number)
    true # do you really need to return true here?
  end

  def with_lock
    with_lock!
  rescue NotAcquired
    false
  end

  private

  # set instance variables in the initializer, but never call them directly.
  attr_reader :redis, :redis_key, :expiration_ms, :nx

  def lock
    redis.set(redis_key, random_lock_number, nx: nx, px: expiration_ms)
  end

  # number is a little decieving here when you call `.to_s` at the end.
  # can you use SecureRandom.uuid instead?
  def random_lock_number
    @random_lock_number ||= SecureRandom.random_number(100_000_000_000_000_000).to_s
  end

  # no need for this to be exposed publicly.
  # calling eval directly is usually a bad idea.
  def unlock
    redis.eval(redis_check_and_delete, [redis_key, random_lock_number])
  end

  def redis_check_and_delete
    &lt;&lt;-LUA
      if redis.call('get', KEYS[1]) == KEYS[2] then
        redis.call('del', KEYS[1])
      end
    LUA
  end
end


And to call it:

RedisLock.new(redis_key: 'key', expiration_ms: 10000).with_lock! { do_something }