Unable to connect to RDS after new OS update maintenance

Hello, The best practice here would be to open up a support case so that the team can check the RDS instance and parameters. If the SG, NACL groups etc are not the issue. The host could be having issues. Did you try logging into the host machine ? What is the state it is in ?

• required – The maintenance action will be applied to the resource and can't be deferred indefinitely.

• available – The maintenance action is available, but it will not be applied to the resource automatically. You can apply it manually.

-next window – The maintenance action will be applied to the resource during the next maintenance window.

• In progress – The maintenance action is in the process of being applied to the resource.

Check this link out- https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_UpgradeDBInstance.Maintenance.html