Cluster endpoint: The endpoint for the whole cluster. You should always use this URL for writes, as it points to the primary.
Instance endpoints: A comma-separated list of all DB instance URLs in the cluster, including the primary and all read replicas. Use these URLs for reads (see "How do you scale this DB?" below).
Port: The port to use to connect to the endpoints above.

TODO: Connectivity and output

For more info, see Connecting to Cloud SQL from External Applications.

You can programmatically extract these variables in your Terraform templates and pass them to other resources (e.g. pass them to User Data in your EC2 instances). You'll also see the variables at the end of each terraform apply call or if you run terraform output.

How do you scale this database?

Storage: Cloud SQL manages storage for you, automatically growing cluster volume up to 10TB.
Vertical scaling: To scale vertically (i.e. bigger DB instances with more CPU and RAM), use the machine_type input variable. For a list of Cloud SQL Machine Types, see Cloud SQL Pricing.
Horizontal scaling: To scale horizontally, you can add more replicas using the instance_count input variable, and Aurora will automatically deploy the new instances, sync them to the master, and make them available as read replicas.

How do you configure this module?

This module allows you to configure a number of parameters, such as backup windows, maintenance window, port number, and encryption. For a list of all available variables and their descriptions, see variables.tf.

Known Issues

Instance Recovery

Due to limitations on the current terraform provider for Google, it is not possible to restore backups with terraform. See https://github.com/terraform-providers/terraform-provider-google/issues/2446