Add 3rd Availability Zone (ap-southeast-1c) to Production VPC

In order to reduce risk to business, we are going to increase reliability of core infrastructure through additional redundancy by adding 3rd AWS Availability Zone (ap-southeast-1c) in Singapore region.

This operation includes :

Create 3 new Subnets (Public, Data, and App Tier)
Modify Route Table Association for Public subnets, adding new Public subnet
Create 2 new Route Tables (for Data and App Tier subnet)
Create 1 Elastic IP for NAT Gateway in new AZ
Create 1 NAT Gateway
Modify DB Subnet Group (tvlk-prod-data), adding new Data subnet
Modify Elasticache Subnet Group (tvlk-prod-app), adding new App subnet
Create several Routes (for peering connections, S3 Endpoint)

The operation scheduled on : 2018-08-02 02:00 (UTC+7)

Should you find any unusual behaviour related to this operation after scheduled time, please report by replying on this thread section and mention @site-infra

Thank you

Reference: https://29022131.atlassian.net/browse/TOSD-3932