lambda_rds.yml

# This template is a Cloud Formation template, that has AWS Sam seamlessly mixed in
# It is extremely powerful as you will see!

# This is a template of Lambda & RDS, publically available (so no private VPC)
AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::Serverless-2016-10-31 # This is to tell cloudformation we need to transform this template, as it has SAM!

Description: Severless set up with an RDS
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Parameters:
  dbUserPassword:
    NoEcho: true
    Type: String
  dbUserName:
    NoEcho: true
    Type: String
  DbSize:
    Type: String
    Default: db.t2.small
## Globals is unique to AWS Sam and is not featured in Cloudformation
## These Globals under Function are passed to each AWS::Serverless::Function as properties
Globals:
  Function:
    Runtime: go1.x
    Timeout: 10
    Tracing: Active
    Tags:
      demo: true
    Environment:
      Variables:
        MY_SQL_URI: !Join ['', [!Ref dbUserName, ':', !Ref dbUserPassword, '@(', !GetAtt DatabaseCluster.Endpoint.Address, ':', !GetAtt DatabaseCluster.Endpoint.Port, ')/mydb']]
    # The powerful intrinsic function Join, here we join a db connection string and make it a global
    # So every lambda function can access it right away!
    
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# The following sections is AWS Sam
# It ties together Lambda functions so they are easy to deploy as you will see
Resources:
  Write:
    Type: AWS::Serverless::Function # This type Serverless::Function is unique to Sam
    Properties:
      Policies:
        - AWSXrayWriteOnlyAccess
      Handler: dist/handler/write # Ofcourse we tell need to mention where the code is
      Events: # It lets you define events that trigger your lambda function
        GetEvent:
          Type: Api # This is an API Gateway event, it automically handles all in & outs of setting up an API gateway with Lambda!
          Properties:
            Path: /write
            Method: get
  Read:
    Type: AWS::Serverless::Function
    Properties:
      Policies:
        - AWSXrayWriteOnlyAccess
      Handler: dist/handler/read
      Events:
        GetEvent:
          Type: Api
          Properties:
            Path: /read
            Method: get

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  PublicDatabaseSubnetGroup:
    Type: AWS::RDS::DBSubnetGroup
    Properties:
      DBSubnetGroupDescription: CloudFormation managed DB subnet group.
      SubnetIds: !Split [ ',',  !ImportValue LambdaVPCExperiementPublicSubnets] 
      # More powerful intrinsic functions, we import the Public Subnets from another stack & split it into a list like SubnetIds require
  DatabaseCluster:
    Type: AWS::RDS::DBCluster
    Properties:
      MasterUsername: !Ref dbUserName
      MasterUserPassword: !Ref dbUserPassword
      Engine: aurora
      DBSubnetGroupName: !Ref PublicDatabaseSubnetGroup
  DatabasePrimaryInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      Engine: aurora
      DBClusterIdentifier: !Ref "DatabaseCluster"
      DBInstanceClass: !Ref DbSize
      DBSubnetGroupName: !Ref PublicDatabaseSubnetGroup
      PubliclyAccessible: true

Check out https://github.com/nathanmalishev/go-lambda-vpc-experiment for the up to date code

Or https://medium.freecodecamp.org/lambda-vpc-cold-starts-a-latency-killer-5408323278dd for the accompanying article

Does this handle updates as well or does it blow the rds instance away?