docs: Add new section to HA topic

website/content/docs/install-boundary/architecture/high-availability.mdx

@@ -31,7 +31,12 @@ The workers must be able to establish a connection to the hosts with which they
 
 Boundary requires an external [Postgres](https://www.postgresql.org/) and [KMS](https://aws.amazon.com/kms/). In the example above, we're using AWS managed services for these components. For Postgres, we're using [RDS](https://aws.amazon.com/rds/) and for KMS we're using Amazon's [Key Management Service](https://aws.amazon.com/kms/).
 
-For more information about configuring the Postgres database for high availability, refer to the [Postgres high availability, load balancing, and replication documentation](https://www.postgresql.org/docs/current/high-availability.html).
+### Database
+
+Boundary controllers must be able to reach the PostgreSQL database.
+If you use a [high availability](/boundary/docs/install-boundary/high-availability) (HA) configuration, then the controllers must have access to the PostgreSQL server infrastructure.
+
+For more information about configuring the Postgres database for HA, refer to the [Postgres high availability, load balancing, and replication documentation](https://www.postgresql.org/docs/current/high-availability.html).
 If you use a managed service, refer to your provider's PostgreSQL high availability documentation.
 
 ### API and console load balancer