Retrieve a connection, construct it if necessary (only configuration
        was passed to us). If a non-string alias has been passed through we
        assume it's already a client instance and will just return it as-is.

        Raises ``KeyError`` if no client (or its definition) is registered
        under the alias.

def get_connection(self, alias='default'):
        """
        Retrieve a connection, construct it if necessary (only configuration
        was passed to us). If a non-string alias has been passed through we
        assume it's already a client instance and will just return it as-is.

        Raises ``KeyError`` if no client (or its definition) is registered
        under the alias.
        """
        # do not check isinstance(Elasticsearch) so that people can wrap their
        # clients
        if not isinstance(alias, string_types):
            return alias

        # connection already established
        try:
            return self._conns[alias]
        except KeyError:
            pass

        # if not, try to create it
        try:
            return self.create_connection(alias, **self._kwargs[alias])
        except KeyError:
            # no connection and no kwargs to set one up
            raise KeyError('There is no connection with alias %r.' % alias)