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cfn-modules / rds-aurora-serverless

RDS Aurora Serverless cluster with secure firewall configuration, encryption, multi AZ, auto scaling, backup enabled, and alerting
Apache License 2.0
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Port, PreferredBackupWindow and PreferredMaintenanceWindow are not supported for serverless DBs #3

Closed ptmclean closed 5 years ago

ptmclean commented 5 years ago

Hi,

I think there is a problem with the updating existing stacks with this template. I haven't been able to find the docs that say why this is the case but updates with the following 3 lines in the AWS::RDS::DBCluster resource fail.

      Port: !FindInMap [EngineMap, !Ref Engine, Port]
      PreferredBackupWindow: !Ref PreferredBackupWindow
      PreferredMaintenanceWindow: !Ref PreferredMaintenanceWindow

Basically to reproduce you just need to deploy a stack twice. The second update will fail with..

You currently can't modify BackupWindow with Aurora Serverless.

I'm not sure if this is a bug with the Amazon or not. It's weird that these parameters are permitted on create but not update.

michaelwittig commented 5 years ago

that might be a simple question, just making sure that we don't miss it: You are not changing the PreferredBackupWindow parameter when updating, right?

ptmclean commented 5 years ago

I played a little more with this, this morning. I thought it was reproducible without any change but it looks like you do need to change something in the template, but you don't need to change the Port PreferredBackupWindow or the PreferredMaintenanceWindow.

I created a repro case here. I'll see how things behave when the properties are not set and if the stack behaves itself without them then I'll PR to remove.

ptmclean commented 5 years ago

I took another look at this and I'm not sure of the best way to proceed. PreferredBackupWindow could likely be removed assuming this template is only looking to support severless aurora as I believe it is ignored anyway.

The other 2 aren't ignored so removing Port and PreferredMaintenanceWindow remove the ability to change the defaults which is not ideal. Any ideas?

michaelwittig commented 5 years ago

Do you have access to AWS support? It sounds like a bug that CloudFormation tries to change the BackupWindow if the parameter does not change?

ptmclean commented 5 years ago

You are right, this is an issue with either the cli CloudFormation. I don't have access to the premium support, but I raised this question in the forum.

It would be great if someone has access to raise a support ticket, but this is not an issue with this repo so I'll close this issue.

michaelwittig commented 5 years ago

thanks for the update! Can you post the cli command you use to update the stack?

michaelwittig commented 5 years ago

I'm seeing the same issue now. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/Aurora.Modifying.html mentions that "Although the preferred backup window can be set for Aurora, the setting is ignored. Aurora backups are continuous and incremental."

Unfortunately, I can not remove the PreferredBackupWindow parameter because this results in "You currently can't modify MaintenanceWindow with Aurora Serverless."

I open a support request...

michaelwittig commented 5 years ago

Support confirmed that this is a bug. Currently a possible workaround is to comment out the following properties:

-  "PreferredBackupWindow", 
- "PreferredMaintenanceWindow" and 
- "Port"
michaelwittig commented 5 years ago

fixed in #8