Invoke the lambda function.

def invoke(stage, async, dry_run, config_file, args):
    """Invoke the lambda function."""
    config = _load_config(config_file)
    if stage is None:
        stage = config['devstage']

    cfn = boto3.client('cloudformation')
    lmb = boto3.client('lambda')

    try:
        stack = cfn.describe_stacks(StackName=config['name'])['Stacks'][0]
    except botocore.exceptions.ClientError:
        raise RuntimeError('This project has not been deployed yet.')
    function = _get_from_stack(stack, 'Output', 'FunctionArn')

    if dry_run:
        invocation_type = 'DryRun'
    elif async:
        invocation_type = 'Event'
    else:
        invocation_type = 'RequestResponse'

    # parse input arguments
    data = {}
    for arg in args:
        s = arg.split('=', 1)
        if len(s) != 2:
            raise ValueError('Invalid argument ' + arg)
        if s[0][-1] == ':':
            # JSON argument
            data[s[0][:-1]] = json.loads(s[1])
        else:
            # string argument
            data[s[0]] = s[1]

    rv = lmb.invoke(FunctionName=function, InvocationType=invocation_type,
                    Qualifier=stage,
                    Payload=json.dumps({'kwargs': data}, sort_keys=True))
    if rv['StatusCode'] != 200 and rv['StatusCode'] != 202:
        raise RuntimeError('Unexpected error. Status code = {}.'.format(
            rv['StatusCode']))
    if invocation_type == 'RequestResponse':
        payload = json.loads(rv['Payload'].read().decode('utf-8'))
        if 'FunctionError' in rv:
            if 'stackTrace' in payload:
                print('Traceback (most recent call last):')
                for frame in payload['stackTrace']:
                    print('  File "{}", line {}, in {}'.format(
                        frame[0], frame[1], frame[2]))
                    print('    ' + frame[3])
                print('{}: {}'.format(payload['errorType'],
                                      payload['errorMessage']))
            else:
                raise RuntimeError('Unknown error')
        else:
            print(str(payload))