Lambda using python 3.6 & boto3 in VPC times out when connecting to Redshift

Question

I am trying to use boto3 in python3.6 to connect to my Redshift cluster using the get_cluster_credentials API. The following code times out 100% of the time when the Lambda function is added to the VPC. It runs without issue when Lambda is not added to the VPC.

I can't figure out if get_cluster_credentials uses the public or private IP to access Redshift. I also can't figure out if there is a way to force it to use one or the other.

import json
import boto3

def lambda_handler(event, context):
    redshiftClient = boto3.client('redshift', region_name='us-east-1')
    cluster_creds = redshiftClient.get_cluster_credentials( DbUser='awsuser',
                                                            DbName='dev',
                                                            ClusterIdentifier='redshift-cluster-1',
                                                            AutoCreate=False)
    print(cluster_creds)

    return {
        'statusCode': 200,
        'body': json.dumps('Hello from Lambda!')
    }

My configuration is very simple. The NACL lets everything (0.0.0.0/0) through on all ports and protocols. MY SG does the same thing.

I have 1 internet gateway defined: igw-0d1e6dcbfdea792b2

I have 1 subnet and 1 routing table in the VPC. The routing table has one rule to map 0.0.0.0/0 --> igw-0d1e6dcbfdea792b2.

I am able to connect from outside AWS to the cluster using SQL Workbench/J without issue.

I have looked at many posts, threads and documents, but cannot figure out what is happening:

AWS Lambda times out connecting to RedShift

Connect Lambda to Redshift in Different Availability Zones

https://github.com/awslabs/aws-lambda-redshift-loader/issues/86

Accessing Redshift from Lambda - Avoiding the 0.0.0.0/0 Security Group

https://aws.amazon.com/blogs/big-data/a-zero-administration-amazon-redshift-database-loader/

Conecting AWS Lambda to Redshift - Times out after 60 seconds

Please help.

Thanks a lot.