def kms_key_arn(kms_client, alias):
  """
  Obtain the full key arn based on the key alias provided
  Args:
    kms_client (boto3 kms client object): Instantiated kms client object. Usually created through create_aws_clients.
    alias (string): alias of key, example alias/proto0-evs-drm.

  Returns:
    string of the full key arn
  """
  try:
    response = kms_client.describe_key(KeyId=alias)
    key_arn = response["KeyMetadata"]["Arn"]
  except ClientError as error:
    raise RuntimeError("Failed to obtain key arn for alias {}, error: {}".format(alias, error.response["Error"]["Message"]))

  return key_arn