def get_source_region(global_cluster_response):
    """
    Get writer region from 'describe_global_clusters' response.
    :param global_cluster_response: output of boto3 describe_global_clusters
    :return: aws region
    """
    clusters = global_cluster_response["GlobalClusters"]
    for cluster in clusters:
        for member in cluster["GlobalClusterMembers"]:
            if member["IsWriter"] is True:
                return member["DBClusterArn"].split(":")[3]
    return "unknown"