def is_valid_host(host):
    """ Check if host is valid.

    Performs two simple checks:
        - Has host and port separated by ':'.
        - Port is a positive digit.

    :param host: Host in <address>:<port> format.
    :returns: Valid or not.
    """
    parts = host.split(':')
    return len(parts) == 2 or parts[1].isdigit()