Partitioning a table by ingestion time means that the data is divided into partitions based on the time when the data was loaded into the table. This allows you to delete or archive old data by setting a partition expiration policy. You can specify the number of days to keep the data in each partition, and BigQuery automatically deletes the data when it expires. This way, you can avoid storing unnecessary data and minimize costs.

To securely connect multiple applications with dynamic public IP addresses to a Cloud SQL instance using public IP, the Cloud SQL Auth proxy is the best solution. This proxy provides secure, authorized connections to Cloud SQL instances without the need to configure authorized networks or deal with IP whitelisting complexities.
Cloud SQL Auth Proxy:
The Cloud SQL Auth proxy provides secure, encrypted connections to Cloud SQL.
It uses IAM permissions and SSL to authenticate and encrypt the connection, ensuring data security in transit.
By using the proxy, you avoid the need to constantly update authorized networks as the proxy handles dynamic IP addresses seamlessly.
Authorized Network Configuration:
Leaving the authorized network empty means no IP addresses are explicitly whitelisted, relying solely on the Auth proxy for secure connections.
This approach simplifies network management and enhances security by not exposing the Cloud SQL instance to public IP ranges.
Dynamic IP Handling:
Applications with dynamic IP addresses can securely connect through the proxy without the need to modify authorized networks.
The proxy authenticates connections using IAM, making it ideal for environments where application IPs change frequently.
Google Data Engineer References:
Using Cloud SQL Auth Proxy
Cloud SQL Security Overview
Setting up the Cloud SQL Auth Proxy
By using the Cloud SQL Auth proxy, you ensure secure, authorized connections for applications with dynamic public IPs without the need for complex network configurations.