Automatically configure and fail-over connections using DNS

[jackwotherspoon]

The Python Connector may be configured to connect to a Cloud SQL instance using a DNS name.

When a connection is configured with a DNS name (instead of an instance name), the connector will query the local DNS for a TXT record. The TXT should contain an instance name matching that DNS name. The connector will use the instance name from the TXT record to connect to the Cloud SQL instance.

The connector will periodically query that DNS. If the instance name in the DNS record changes, the connector will terminate all open connections to the old instance. Then, it will reconfigure itself to open connections to the new instance.

This enables several DNS-related features by allowing configuration through DNS.

• Users can configure their database clients using the domain name instead of the instance name.
• Users can fail-over database clients when they change the DNS entry for the database instance.