Whitelisting is the exercise of explicitly allowing access to some identified entities.
To integrate your database with Atlan, it is necessary that it whitelists Atlan and allow it to crawl data from it.
Usually, public traffic is not allowed on database services. They are also not kept in the public network. All to maintain database security.
Hence, to connect databases from outside of databases dedicated network the source IP should be whitelisted in the firewall at the database service end.
Users will have to whitelist the Atlan VPC NatIP in the firewall of the Database network.
For AWS, you can configure it inside the 'Security Groups' option. Refer to the help article published by AWS to get a step-by-step guide - Working with DB Security Groups
For Azure, configure it inside 'Network Security Groups'. Check out the step by step guide here - Configure Azure Storage Firewalls and Networks.