def poll_for_server_running(job_id):
    """
    Poll for the job to start running and post the SERVER_READY_TAG.
    """
    sys.stdout.write('Waiting for server in {0} to initialize ...'.format(job_id))
    sys.stdout.flush()
    desc = dxpy.describe(job_id)
    # Keep checking until the server has begun or it has failed.
    while(SERVER_READY_TAG not in desc['tags'] and desc['state'] != 'failed'):
        time.sleep(SLEEP_PERIOD)
        sys.stdout.write('.')
        sys.stdout.flush()
        desc = dxpy.describe(job_id)

    # If the server job failed, provide friendly advice.
    if desc['state'] == 'failed':
        msg = RED('Error:') + ' Server failed to run.\n'
        msg += 'You may want to check the job logs by running:'
        msg += BOLD('dx watch {0}'.format(job_id))
        err_exit(msg)
Poll for the job to start running and post the SERVER_READY_TAG.